1997 C1500, 4.3L random misfire, at constant speed

Hello,
I have a problem with my truck that my local mechanic cannot seem to figure out. Maybe someone on this forum could help.
I have a 1997 Chevy truck 1500 series. It has a 4.3L engine, 4L60 transmission. The truck starts good and idles good. But, it misses at a constant speed from (take off to level out), It does not misfire (or jerk or shake) while it is under a load. My mechanic checked the ECM for codes and found a P300 random cylinder misfire. I replaced the cap, rotor, wires, plugs and pick up coil (all AC Delco parts). No change in the performance what so ever. Has anyone had or know of anyone having a problem like this? Please, any help would be great.:banghead:

Hello,
I have a problem with my truck that my local mechanic cannot seem to figure out. Maybe someone on this forum could help.
I have a 1997 Chevy truck 1500 series. It has a 4.3L engine, 4L60 transmission. The truck starts good and idles good. But, it misses at a constant speed from (take off to level out), It does not misfire (or jerk or shake) while it is under a load. My mechanic checked the ECM for codes and found a P300 random cylinder misfire. I replaced the cap, rotor, wires, plugs and pick up coil (all AC Delco parts). No change in the performance what so ever. Has anyone had or know of anyone having a problem like this? Please, any help would be great.:banghead:
Good ac delco cap and plugs?
Low fuel pressure or ign problems can give misfires.
Needs to be put on a good engine capable scanner and read out what and how many times the cylinders are misfiring.
Also check camshaft retard setting in scanner.

Make sure fuel pressure is up to par.

Replaced cap and plugs with genuine Delco parts. I took the truck to another mechanic and found that the fuel pressure is too low, he is going to check out furhter and let me know by Saturday. Thanks for the help.

I have a 97 C1500 4.3L Base truck. I love the truck and she starts instantly and idles perfectly...Put it in gear and she takes off fine under load and then just before she shifts (few seconds before) she stumbles and misfires and I get a P301 code....then she shifts to next gear and smooths right on out until next shift.....

1.) My book says 60-66psi. Is that right?
2.) My truck is giving me 56-58psi at the rail.

Before I got that I was at 52-54 and the truck was backfiring and acting/running terrible. Using WAY too much fuel. So, I took the plenum off and changed the fuel pressure regulator (a used one, I know that was stupid). I noticed an immediate improvement and pressure at 58 or so.

Now I'm stuck with a very minor (as explained) mis and studder near the shift points. Could it be that I need to put a NEW regulator on it to get the pumps 60-66 psi capabilities or do I need to put a pump in it?

I would love to check the pressure short of the regulator but don't know how. I really think it may be regulator because the pump with key on is INSTANT to 58. I mean it takes 1-2 seconds and it is solid 58 and holds for 20 min with key off.

Hope this bit of information from me helps someone and hope someone can verify what they think I should do in my situation.

Had the spider thing off and injector tips / poppets looked very clean (sprayed off with carb cleaner anyway).

Thanks for you help.

Mr. Tripp
Augusta, GA

I have a 97 C1500 4.3L Base truck. I love the truck and she starts instantly and idles perfectly...Put it in gear and she takes off fine under load and then just before she shifts (few seconds before) she stumbles and misfires and I get a P301 code....then she shifts to next gear and smooths right on out until next shift.....

1.) My book says 60-66psi. Is that right?
2.) My truck is giving me 56-58psi at the rail.

Before I got that I was at 52-54 and the truck was backfiring and acting/running terrible. Using WAY too much fuel. So, I took the plenum off and changed the fuel pressure regulator (a used one, I know that was stupid). I noticed an immediate improvement and pressure at 58 or so.

Now I'm stuck with a very minor (as explained) mis and studder near the shift points. Could it be that I need to put a NEW regulator on it to get the pumps 60-66 psi capabilities or do I need to put a pump in it?

I would love to check the pressure short of the regulator but don't know how. I really think it may be regulator because the pump with key on is INSTANT to 58. I mean it takes 1-2 seconds and it is solid 58 and holds for 20 min with key off.

Hope this bit of information from me helps someone and hope someone can verify what they think I should do in my situation.

Had the spider thing off and injector tips / poppets looked very clean (sprayed off with carb cleaner anyway).

Thanks for you help.

Mr. Tripp
Augusta, GA

You are welcome and we are glad to help.

You will need afuel pressure gauge that you can hook up to truck and drive on road and watch fuel pressure while driving it.
Like gauge taped to outside windshield or outside mirrow.

Fuel pressure specs are 60/66 on that engine.

If pressure is low block off or plug return line and see if fuel pump pressure comes up to 95/105 lbs pressure.
Just do not run pump at full pressure over a second or 2.

Direct fuel pump pressure has to be up over the regulated regulator specs and also have enought volumn to hold regulated pressure.

Code 301 points to miss on no 1 cylinder.

Make sure good compression and plugs and cap and rotor and wires on that cylinder.

Beside low fuel pressure The camshaft retard setting and secandary ign and even MAF sensor and other sensors can create a miss fire.
A good place to start is to.
Work on getting the fuel pressure up to specs.



The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Guide lines on checking fuel pressure and pump test.

Hard to start cold or hot or low fuel pressure and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

I did go up under the truck and put a pair of vise-grips on the return line. Got up and started the truck...it just sat there and purred like a kitten....fuel pressure rose to maybe 62 and that was it. It did not go way high and start spitting out black smoke or anything.....I was left thinking I had some kind of leak down....fuel was not going aywhere that I could see.

Is it just that the pump is not able to pump more than that? IDK

Key on pressure: 56 in less then 2 seconds.
Turn off: Pressure holds for 20 min or so without dropping much at all.

Start engine: Pressure may be 58 if that.

Pinch of return line: Pressure may go to 60 to 62 and that is it.

I'm beginning to think pump. Truck has 214,000 miles on it and purrs like a kitten except for the hesitation/stutter.

Ayup, it's the pump. A pinched return line should shoot the pressure high as mentioned.

Spend the extra money and get a Delco pump. You'll save yourself the pain of replacing it a year from now if you use a parts store brand such as Airtex.

Good luck!

Thanks...I'll get a good pump. Just can see why people choose the lesser one...the cost of the pump is ridiculous.

Tks

I will try to remember to post back after I finish the install and tell if that was the solution completely.

Hey everyone!

Can you tell me how to find the fuel pump alone and not the whole module?

I am allergic to paying too much for a module I don't need. I just want the pump and strainer and I can fix the rest.

Also, we have a "Pull-A-Part" major chain used auto parts yard and I may be able to get lucky and find a low mileage vehicle with same pump/module. I know many would not recommend this but when you are on a budget you do funny things and I have been very lucky with used parts in my life.

What vehicles would I be looking for that would have the same pump? Many have the same pump but the module is different and therefore they say it won't interchange but it is the same pump.....any info?

Tks

The AC- Delco pump is usually known as and goes by Delphi fuel pump.

Cost about 25$ more than junk Airtex and aftermarket pumps.
And a lot of places you have to special order them.
But usually only overnight.
Carquest is about the only place that carries the Delphi pump in stock.
They have dropped the other brands like a hot spud.
Some parts places only stock and pusk the junk ones.
If so get on ther case and tell the Delphi is the only one you want.

Other things beside the pump can give also give low fuel pressure.
Like wiring and plug ins and grounds and voltage to pump and fuel pump relay to pump and fuel filter plugged.
It is always best to go threw the full fuel pressure test before and after replacing the pump.

The AC- Delco pump is usually known as and goes by Delphi fuel pump.

Cost about 25$ more than junk Airtex and aftermarket pumps.
And a lot of places you have to special order them.
But usually only overnight.
Carquest is about the only place that carries the Delphi pump in stock.
They have dropped the other brands like a hot spud.
Some parts places only stock and pusk the junk ones.
If so get on ther case and tell the Delphi is the only one you want.

Other things beside the pump can give also give low fuel pressure.
Like wiring and plug ins and grounds and voltage to pump and fuel pump relay to pump and fuel filter plugged.
It is always best to go threw the full fuel pressure test before and after replacing the pump.

Hey everyone!

Can you tell me how to find the fuel pump alone and not the whole module?

I am allergic to paying too much for a module I don't need. I just want the pump and strainer and I can fix the rest.

Also, we have a "Pull-A-Part" major chain used auto parts yard and I may be able to get lucky and find a low mileage vehicle with same pump/module. I know many would not recommend this but when you are on a budget you do funny things and I have been very lucky with used parts in my life.

What vehicles would I be looking for that would have the same pump? Many have the same pump but the module is different and therefore they say it won't interchange but it is the same pump.....any info?

Tks
On a buget I can understand looking for a way to save a buck.
But.

There is few short cuts or ways to save money on a good fuel pump.
Outside of checking around/pricing the delphi parts.
Some places will give a better price on them.
After pricing around for best deal.
Best to just back up to the parts counter where they can bite you in the rear and tell them you need a New Delphi fuel pump module.

Like My uncle always said the good stuff only hurts one time.

Cheap parts or bone yard stuff can bite you in the rear many times.


Fuel pump alone are very hard to replace in the module.
Due to the plastic lines connecting the pump to fuel lines and wiring confirration.
And pulling one from a salvage yard there is a slim chance of getting a real good pump.

Bad fuel pump cold even be the reason it is in the bone yard.

If you are going to bone yard it i would try to get the complete tank that will fit you truck.

Good Luck and let us know how it goes.

Thanks for the information. I have located a local parts house that sells CARTER fuel pumps. What do you think about this name? IMHO it is a better brand then the knockoffs but not sure how it stands up to Delphi which is a part of GM right? Tks

Thanks for the information. I have located a local parts house that sells CARTER fuel pumps. What do you think about this name? IMHO it is a better brand then the knockoffs but not sure how it stands up to Delphi which is a part of GM right? Tks

You are welcome.
Carter is a very old brand and maker of many older fuel pumps.
May even be older than I am and that is old.
I have used many Carter older type fuel pumps over the last 50 years with no problems.

But the newer high pressure fuel injection pumps are a different breed.

Airtex and other brands used to make good fuel pumps to but went down hill.
Some even sold out there brand to make and supply cheaper fuel pumps.

Yes Delphi has replaced AC-delco and most GM fuel pumps are made and branded by Delphi.

Delphi also makes a lot of other electrical parts for GM OEM.

Not sure but I would supect GM has stock in Delphi or GM big shots are sleeping in bed with Delphi big shots.

As far as Carter Brand Pumps ask your parts place how many Carter pumps High pressure for GM they have sold that handles them and what the fail rate is on them.

How does the Carter Price tag stack up with Delphi pumps?
Do they sell only have Carter or other brands?

White Brothers Auto Parts here In Augusta, GA has the pump for around 158.00 but they said, if it has GHPV or INOP...all types of different letters on the top of the pump to get the right one....

they say it depends on the pump it requires and that I should call the dealer and see which one it calls for.....GMAB!

Sooooo, guess I have to take it off and hope that after 214,000 miles that it has the original pump and has the letters legible so I can tell them what pump I need.

Tks

White Brothers Auto Parts here In Augusta, GA has the pump for around 158.00 but they said, if it has GHPV or INOP...all types of different letters on the top of the pump to get the right one....

they say it depends on the pump it requires and that I should call the dealer and see which one it calls for.....GMAB!

Sooooo, guess I have to take it off and hope that after 214,000 miles that it has the original pump and has the letters legible so I can tell them what pump I need.

Tks

JUST PUMP OR THE HOLE FUEL PUMP MODULE?

As said you should replace the complete module.

The only numbers I have found on them is a tag on wiring harness or tag on top of module.

My parts depatment only shows one pump/module but it comes with a wiring change over.

Used the work pump and hanger? I believe this is the whole module.

Used the work pump and hanger? I believe this is the whole module.

If wiring plug-in is different you can buy plug-in wiring kits.

Good Luck and let us know how it goes.

Follow up and hopefully final:

1.) Removed bed (8) bolts used two jackstands on rear tires (e-brake on) and picked up one side of the bed at a time as I jacked the jack stands to their full height giving me (all by myself) access to the tank as the bed tilted back. Make sure you put two rags at the back of the bed where it will tilt against bumper and don't forget ground strap at front of bed. Was easy and one person job. Yes I'm sore...ha.

2.) Old module came out fine with a couple of exceptions. (1) the fuel connections are almost impossible to get off....the release tool is too wide to get into the opening. Solution, just make sure you relieve the fuel pressure at the fuel rail and then just simply break them off like you would with a crab leg. Then when the hose is off the pump with a piece of plastic sticking out of it. (should have used tool and broke it off to permit it to be as long as I could sticking out) Place tool onto fuel line and then screw wood screw into plastic piece that is in there and just pull it out. (2) Pump did not want to go back in at all...the fit is VERY tight and I was almost to the point of breaking it as the new o-ring and pump was pressed into the hole. Liked the old non-snap ring kind better.

3.) Be advised, GM will make you change your 4-wire fitting to the new one. This will require you to cut and rewire your electrical fitting. I should have made a Youtube video on it. The problem was that the pump tells you to wire up to the colors and they are different. The truck wiring has the Black and Grey that go to the pump and then another smaller guage black and a purple with trace wire going to the tank level sensor. The new pump comes with the black and grey, a purple and an orange wire. The Orange wire is the one that goes to the non-purple smaller black wire. Take your time here and you may want to as I did, insert the pump, connect and test with key on. DANGER - fumes from the tank could be an issue if you are VERY unlucky. Be careful.

**Also, it has you put a package of dialectic(sp) greese of some sorts into the connector...I forgot and mine runs fine...hope I don't have to take it off at a later date.

4.) Car had only 62 psi at key on and then flipped back to 58. Pinched off the return and it shot to 100. So, then I knew that I had a better pump in there. Started the truck, drove it around the block and it was acting no better at all. Drove right to Advance Auto Parts and bought a Fuel Pressure regulator. It looked a bit different but after putting it in and back together it runs great. I notice as I drive it with the gauge that it does not hold 61 psi while driving and according to the factory where they say it should have 60-66...???? This truck purrs like a brand new truck at 58psi and then as I flip the throttle it will jump to 61-62. On the driving test, every time I push the gas to take off it will shoot up to 62 or so. The drivability issues are all gone. It accelerates hard and no hesitation or skipping or codes. But still not steady 60-66??? Needless to say, I'm happy.

I am still confused however about the leak down. At first before changing the FPR I could hold 56-58 psi for well over a minute. Now with new pump and FPR as soon as I let go of the key my FP goes back to 0 within 30 seconds. Pumps to 64 instantly and starts right up but fuel leaks down. At times while I was checking I would pinch return just after pump shut off, no change with leak down, then pinch supply just after pump shuts off (key off) and the leakdown was the same. Then my son had an idea...we disconnected the fuel supply line at the rail, he put his finger over it and hit the key, pressurized to nearly 100psi instantly and the shut off. As he sat there and held his hurting finger (27yo) on supply the pressure was clearly dropping faster then it should. So, I thought I had bad pump with check valve problem. But, car runs great so I don't want to complain. While checking I had all plugs out and they were perfectly clean and I had all poppets out to check if the injectors were leaking too...no leaks???? Where the hell was all the fuel going.

WARNING: Truck started up and was knocking a bit. This was due (I found out) to the small pieces of popit that broke off in my hands under the upper intake. Be very careful as these poppets were very fragile. I got lucky here. One other lock moment was when I noticed that the distributor hold down cast iron piece at the back of the distributor was broke and as I grabbed for it it fell into the top of the valley / intake area near an intake rail. 2 inches to the left and it would have went down into the engine. Advice: When you take the upper plenum off to change FPR please stuff rags into the rails. Good idea.

Follow up and hopefully final:

1.) Removed bed (8) bolts used two jackstands on rear tires (e-brake on) and picked up one side of the bed at a time as I jacked the jack stands to their full height giving me (all by myself) access to the tank as the bed tilted back. Make sure you put two rags at the back of the bed where it will tilt against bumper and don't forget ground strap at front of bed. Was easy and one person job. Yes I'm sore...ha.

2.) Old module came out fine with a couple of exceptions. (1) the fuel connections are almost impossible to get off....the release tool is too wide to get into the opening. Solution, just make sure you relieve the fuel pressure at the fuel rail and then just simply break them off like you would with a crab leg. Then when the hose is off the pump with a piece of plastic sticking out of it. (should have used tool and broke it off to permit it to be as long as I could sticking out) Place tool onto fuel line and then screw wood screw into plastic piece that is in there and just pull it out. (2) Pump did not want to go back in at all...the fit is VERY tight and I was almost to the point of breaking it as the new o-ring and pump was pressed into the hole. Liked the old non-snap ring kind better.

3.) Be advised, GM will make you change your 4-wire fitting to the new one. This will require you to cut and rewire your electrical fitting. I should have made a Youtube video on it. The problem was that the pump tells you to wire up to the colors and they are different. The truck wiring has the Black and Grey that go to the pump and then another smaller guage black and a purple with trace wire going to the tank level sensor. The new pump comes with the black and grey, a purple and an orange wire. The Orange wire is the one that goes to the non-purple smaller black wire. Take your time here and you may want to as I did, insert the pump, connect and test with key on. DANGER - fumes from the tank could be an issue if you are VERY unlucky. Be careful.

**Also, it has you put a package of dialectic(sp) greese of some sorts into the connector...I forgot and mine runs fine...hope I don't have to take it off at a later date.

4.) Car had only 62 psi at key on and then flipped back to 58. Pinched off the return and it shot to 100. So, then I knew that I had a better pump in there. Started the truck, drove it around the block and it was acting no better at all. Drove right to Advance Auto Parts and bought a Fuel Pressure regulator. It looked a bit different but after putting it in and back together it runs great. I notice as I drive it with the gauge that it does not hold 61 psi while driving and according to the factory where they say it should have 60-66...???? This truck purrs like a brand new truck at 58psi and then as I flip the throttle it will jump to 61-62. On the driving test, every time I push the gas to take off it will shoot up to 62 or so. The drivability issues are all gone. It accelerates hard and no hesitation or skipping or codes. But still not steady 60-66??? Needless to say, I'm happy.

I am still confused however about the leak down. At first before changing the FPR I could hold 56-58 psi for well over a minute. Now with new pump and FPR as soon as I let go of the key my FP goes back to 0 within 30 seconds. Pumps to 64 instantly and starts right up but fuel leaks down. At times while I was checking I would pinch return just after pump shut off, no change with leak down, then pinch supply just after pump shuts off (key off) and the leakdown was the same. Then my son had an idea...we disconnected the fuel supply line at the rail, he put his finger over it and hit the key, pressurized to nearly 100psi instantly and the shut off. As he sat there and held his hurting finger (27yo) on supply the pressure was clearly dropping faster then it should. So, I thought I had bad pump with check valve problem. But, car runs great so I don't want to complain. While checking I had all plugs out and they were perfectly clean and I had all poppets out to check if the injectors were leaking too...no leaks???? Where the hell was all the fuel going.

WARNING: Truck started up and was knocking a bit. This was due (I found out) to the small pieces of popit that broke off in my hands under the upper intake. Be very careful as these poppets were very fragile. I got lucky here. One other lock moment was when I noticed that the distributor hold down cast iron piece at the back of the distributor was broke and as I grabbed for it it fell into the top of the valley / intake area near an intake rail. 2 inches to the left and it would have went down into the engine. Advice: When you take the upper plenum off to change FPR please stuff rags into the rails. Good idea.
You did not say if you used a delphi fuel pump.
If you did not use a delphi fuel pump you can have many more problems pop up.

But if it starts good and runs good you have fixed your problem for the time being.

On the pressure I would confirm that your fuel pressure gauge is reading right on the money.
Best test is with another know good gage.

Very dangerous to hold fuel pressure or oil pressure with the finger.:nono::nono:
I had a freind that shot his finger full of greese with a greese gun and about lost his finger.
A hundred lbs of fuel pressure can inject the finger full of gas.

On pressure leak down pressure can also leak back into the fuel pump if check valve is bad.
Best way to check for that is to hook your gage direct to the fuel filter in line.
Then crank up pressure and watch for fast leak down.
If a fast leak down there it is leaking back threw fuel pump or lines to fuel pump.

Cold start engine cranking fuel pressure needs to be 64-65 lbls
Anything under that will cause injectors not to squirt on a cold start.
Engine running and running on the road fuel pressure will range 62-65 lbs depending on engine load.

Full load it should jump 65-66 lbs.
Coast or no load it can drop to 60-62 lbs.
Steady down the road you should see around 63-64.
The fuel pressure regulator works off of engine vacuum.
Full load with low or no vacuum on it it goes to full pressure.
High vacuum or coasting it goes to the lower pressure.
Depending on engine vacuum it can and should range to specs of 60/66 lbs pressure.

But you need a very accurate gage for testing.
Always check your gage with a known good Gage.

The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a Gage to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

Also see http://www.automotiveforums.com/vbulletin/showthread.php?t=1058349

My pressure on start up does go very close to 64-65. Drops back and runs (idles) like a new car at 58 or so. This is less then what you say it should be.

Driving around pressure is about 62-63 as demand increases the pressure increases but never more than 62.

The leak down is much faster than it was with the old pump. Before with original pump I could hold after pumping up to 60, for 1 min or more and would still have 50 or more. Now with new pump I have zero pressure after a minute or two. But runs well in all ranges.

I couldn't check it off the filter because I didn't have the connections.


OHHH, the pump I bought was a CARTER fuel pump. Nearly 200.00 for it. Best deal I could find and when pinching the return it will pump closer to 100 pounds vs 75 or so as you stated.

I wonder if I don't have a vacuum issue as where the MAF goes in or where the injector body seals around the upper intake and where the brake booster connects in etc...there are plenty of places where I could be leaking air to the outside. Would this affect the "vacuum" of the fuel pressure regulator?

Remember, this is not the FPR that has a vacuum line going to it. It is a Central Fuel Injection vehicle with the FPR under the upper plenum (plastic) behind the injector module. It has a vacuum like connector on the bottom but it just hangs out in the wind so to speak.

Tks

My pressure on start up does go very close to 64-65. Drops back and runs (idles) like a new car at 58 or so. This is less then what you say it should be.

Driving around pressure is about 62-63 as demand increases the pressure increases but never more than 62.

The leak down is much faster than it was with the old pump. Before with original pump I could hold after pumping up to 60, for 1 min or more and would still have 50 or more. Now with new pump I have zero pressure after a minute or two. But runs well in all ranges.

I couldn't check it off the filter because I didn't have the connections.


OHHH, the pump I bought was a CARTER fuel pump. Nearly 200.00 for it. Best deal I could find and when pinching the return it will pump closer to 100 pounds vs 75 or so as you stated.

I wonder if I don't have a vacuum issue as where the MAF goes in or where the injector body seals around the upper intake and where the brake booster connects in etc...there are plenty of places where I could be leaking air to the outside. Would this affect the "vacuum" of the fuel pressure regulator?

Remember, this is not the FPR that has a vacuum line going to it. It is a Central Fuel Injection vehicle with the FPR under the upper plenum (plastic) behind the injector module. It has a vacuum like connector on the bottom but it just hangs out in the wind so to speak.

Tks

Your pressure is good or it would not start cold good and run good.
If it idles and runs good then you do not have any vacuum leak problems.
The fuel pressue regulator gets it vacuum from inside the engine under upper intake.

Was it a complete carter fuel pump module or just a carter pump that you had to install inside module?
If it was not a complet Delphi module or you tryed to install a fuel pump into your old module you problem may be there.

Off hand I would say you gauge is not quite reading right on pressure.
Check it against a know good gauge.
If a couple persent off it can show 4-5 lbs off on readings.

As to the fast leak down you would need to check if leak down is in the pump or pump lines or towards fuel regulator or injector or lines in that direction.

A fast leak down is not good and points to a problem but if fuel system is holding good pressure it will start and run all day with a fast leak down engine off.
But with a fast leak down engine off you need to find and check it out or it may start giving engine running problems later on.
A pump check valve leak back is not a bad as a fuel pump module line keaking off.

Let us know how it goes and if you tryed to just replace the pump using your old module?

Full pressure specs and cut off specs on a Delphi pump is up to 100-105 lbls
The 75 LBs I stated is what the pump needs for the regulator to maintain specs of 60/66.
BUT THE MORE UP TO 105 THE BETTER YOUR PUMP IS .
Also pump needs good fuel volumn.

Understand on the leak back with the line (gas on ground or leaking out of system) and check valve leak (gas is returning back to the tank).

I will call the place and see what the warranty is and may try to verify the very fast leak down and a bad check valve. Then if that is the case I may just option the warranty and put another pump in.

I was 10min from cutting a door into the bed (saw it on youtube) and having a very professional looking access door as I usually have the bed liner in it anyhow. But at last minute I did the 1-man job of lifting the bed and the dangerous (I guess) getting under a tilted/supported bed and doing the procedure. Kind of liken it to going through a small hole in the ribs, vs cracking the chest in open heart surgery...ha.

Tks

Understand on the leak back with the line (gas on ground or leaking out of system) and check valve leak (gas is returning back to the tank).

I will call the place and see what the warranty is and may try to verify the very fast leak down and a bad check valve. Then if that is the case I may just option the warranty and put another pump in.

I was 10min from cutting a door into the bed (saw it on youtube) and having a very professional looking access door as I usually have the bed liner in it anyhow. But at last minute I did the 1-man job of lifting the bed and the dangerous (I guess) getting under a tilted/supported bed and doing the procedure. Kind of liken it to going through a small hole in the ribs, vs cracking the chest in open heart surgery...ha.

Tks


Also it can leak at the line inside fuel module where it connects to pump and the pressure line to filter.
Very commom problem unless you replaced the complete module.
As askek several times in upper post.
Which way did you go a complete module or just pump replacement?

Used brand new CARTER fuel pump module bought from White Brothers Automotive with warranty.

Seems like if the line was leaking on the hose from the fuel pump to outlet at top of module that I would not get 100+ psi. If was leaking from top of module to filter I would have fuel on the ground. Right?

Tks

Used brand new CARTER fuel pump module bought from White Brothers Automotive with warranty.

Seems like if the line was leaking on the hose from the fuel pump to outlet at top of module that I would not get 100+ psi. If was leaking from top of module to filter I would have fuel on the ground. Right?

Tks

You can still get a 100 lbs of pressure with leak.
If you tap into fuel filter inline and pump up to full presure and still have a fast leak down it is leaking back towards pump or out the check valve in pump.
Only proper testing will tell you where the leak is.

That is one reason why we advised you to use only the Delph brand pump pump.
You still have a problem and
The extra money you save on the after market stuff can cost you more in the long run in labor and down time and extra head aces.

Good Luck

I sure know the "good money after bad" story but I went with CARTER who have been making fuel related accessories for decades. Not really the same as buying one for 90.00 from Advance or Auto zone. But still, I get the message.

Thanks for all of your help and I will be watching it closely.

I sure know the "good money after bad" story but I went with CARTER who have been making fuel related accessories for decades. Not really the same as buying one for 90.00 from Advance or Auto zone. But still, I get the message.

Thanks for all of your help and I will be watching it closely.

You are welcome and glad to help.

If just the check valve leaking off it may run a long time like that.
The check valve is to hold pressure after pump is shut off.
But.
You may have to prime it up by a couple of key off and on's to get a good start up.

Yes carter and also Airtex are both know good old brands.

I have used there low presure manual pumps for 50 years with few problems.
But Airtex now puts out junk high pressure pumps.
Carter I have never tester or had any experiance with the gm high pressure pumps.
But that hundred dollars cheaper price makes me wonder about them and also you getting a defective one first time makes me wonder even more.
Ever parts store besides Carquest push Airtex even knowing they have a high fail rate.
Carquest dropped Airtex like a hot spud after many comback on them.
They have went to all Delpi on GM high pressure pumps.
I would say airtex has sold out there brand to make cheaper junk pumps so parts places can under cut Delphi price and so the parts place can make more profit at the costomer expense in the long run.

I always go with Delphi pumps.
And most parts places on 25$ more than Airtex pumps
Very low fail rate or problems.
May be 1 out of a hundred.
I just had a call about one I installed on a blazer used on a country mail route 3 years ago that the customer said failed.
But customer did not bring it back for me to test it out.
Only called my wife to complain about it.
Would not even talk to me when my wife asked her to.
So I can even not tell for sure it was a bad one or other problems caused the fail.
A lot of times people run the to low or out of gas or get bad gas let there fuel filter stop up and bad wiring to fuel pump.

Thanks for posting back and keeping us informed on how it went
Good luck and let us know how it goes.

How does this fit into the picture with the random misfire.

I'm not being told that it is definitely my timing. As discussed before the 97 c1500 4.3L can not be adjusted say with a timing light and distributor has really only one way to go in. There is an arrow on the distributor body and it has to be lined up with the rotor when the engine is TDC on #1.

Well, this shade tree did just that, I verified with timing mark and a balloon on my compression guage. ((Hooked up balloon and I could visibly see when the blowing (filled balloon) and sucking intake (air got sucked back out of balloon) showed the piston to be at the absolute very top of its compression stroke. Now you believe me...ha.))

The engine WAS TDC #1 Compression and the distributor was pointing at the number one tower but more importantly at the plastic arrow on the distributor base.

Truck started up and purred like a kitten.....now....

Today after weeks of it doing exactly the same thing, missing just before it shifts as rpm's rise and then under load spiting and sputtering at times making me think fuel....We hooked it up to an advanced MODIS computer system and it showed that the base timing was set at -25 and needed or should be at 0. The ECCS was advancing the timing so that it would run almost perfect but -25 is too much and under a load is where it will be shown.

Now, why the heck would it be -25 if the distributor was installed correctly. Why wouldn't the base timing be 0 to indicate the distributor was in correctly?

Well mechanic says that only way to get it right is to hook up the computer and play with the timing on the little slack that the hold down gives you and if that don't work then you have to pull the distributor barely out and move it one tooth advanced...(which way would that be?) and then start it back up until you get it to where the base timing is set at 0.

Does this make any sense to any of you? Tks for your imput as that is what I'm about to try here.

Also code I'm getting is Low Efficiency Bank 1??? Don't know if this would be related to the skip and subsequent gas/o2 levels related to the skip.??? Tks for your input.

How does this fit into the picture with the random misfire.

I'm not being told that it is definitely my timing. As discussed before the 97 c1500 4.3L can not be adjusted say with a timing light and distributor has really only one way to go in. There is an arrow on the distributor body and it has to be lined up with the rotor when the engine is TDC on #1.

Well, this shade tree did just that, I verified with timing mark and a balloon on my compression guage. ((Hooked up balloon and I could visibly see when the blowing (filled balloon) and sucking intake (air got sucked back out of balloon) showed the piston to be at the absolute very top of its compression stroke. Now you believe me...ha.))

The engine WAS TDC #1 Compression and the distributor was pointing at the number one tower but more importantly at the plastic arrow on the distributor base.

Truck started up and purred like a kitten.....now....

Today after weeks of it doing exactly the same thing, missing just before it shifts as rpm's rise and then under load spiting and sputtering at times making me think fuel....We hooked it up to an advanced MODIS computer system and it showed that the base timing was set at -25 and needed or should be at 0. The ECCS was advancing the timing so that it would run almost perfect but -25 is too much and under a load is where it will be shown.

Now, why the heck would it be -25 if the distributor was installed correctly. Why wouldn't the base timing be 0 to indicate the distributor was in correctly?

Well mechanic says that only way to get it right is to hook up the computer and play with the timing on the little slack that the hold down gives you and if that don't work then you have to pull the distributor barely out and move it one tooth advanced...(which way would that be?) and then start it back up until you get it to where the base timing is set at 0.

Does this make any sense to any of you? Tks for your imput as that is what I'm about to try here.

Also code I'm getting is Low Efficiency Bank 1??? Don't know if this would be related to the skip and subsequent gas/o2 levels related to the skip.??? Tks for your input.

TIMING IS NOT ADJUSTABLE.
The computer sets it where it wants to be.

What is the camshaft retart reading?

What is the fuel pressure readings?

There, now I know that you know what I'm talking about. (I've always thought that MT..ha) The Camshaft retard is -25 what the mechanic was talking about. I was talking and calling it the "base timing".

Fuel pressure settings on my gauge is starting at 62 or so, dropping to 58 at idle and purring like a kitten, then as I drive down the road under load it is staying 60-62 psi. A bit more if I demand more power.

GT

How does this fit into the picture with the random misfire.

I'm not being told that it is definitely my timing. As discussed before the 97 c1500 4.3L can not be adjusted say with a timing light and distributor has really only one way to go in. There is an arrow on the distributor body and it has to be lined up with the rotor when the engine is TDC on #1.

Well, this shade tree did just that, I verified with timing mark and a balloon on my compression guage. ((Hooked up balloon and I could visibly see when the blowing (filled balloon) and sucking intake (air got sucked back out of balloon) showed the piston to be at the absolute very top of its compression stroke. Now you believe me...ha.))

The engine WAS TDC #1 Compression and the distributor was pointing at the number one tower but more importantly at the plastic arrow on the distributor base.

Truck started up and purred like a kitten.....now....

Today after weeks of it doing exactly the same thing, missing just before it shifts as rpm's rise and then under load spiting and sputtering at times making me think fuel....We hooked it up to an advanced MODIS computer system and it showed that the base timing was set at -25 and needed or should be at 0. The ECCS was advancing the timing so that it would run almost perfect but -25 is too much and under a load is where it will be shown.

Now, why the heck would it be -25 if the distributor was installed correctly. Why wouldn't the base timing be 0 to indicate the distributor was in correctly?

Well mechanic says that only way to get it right is to hook up the computer and play with the timing on the little slack that the hold down gives you and if that don't work then you have to pull the distributor barely out and move it one tooth advanced...(which way would that be?) and then start it back up until you get it to where the base timing is set at 0.

Does this make any sense to any of you? Tks for your imput as that is what I'm about to try here.

Also code I'm getting is Low Efficiency Bank 1??? Don't know if this would be related to the skip and subsequent gas/o2 levels related to the skip.??? Tks for your input.

Oh MY.
This sounds like a unusall problem.

Back to when you set dist. base seting with the pointer at the 6 at at TDC compression.
The truck ran good at that time?
Did the computer show correct camshaft retard of 0 degrees at that time?

If I read your post right after 2 week the truck started missing and camshaft retard was at - 25 degrees camshaft retard?

If so the dist seting had to move somehow.
Either hold down letting dist move or roll pin in dist gear sheared.
Or camshaft position senser bad or dead or the plugin wire not making connection.
Have you checked the dist hold down and the dist gear roll pin.

What code no is the VCM/PCM setting.

I would start with rechecking the Dist rotor at the no. 6 TDC compression.
If it is still there and the computer is reading -25 degrees camshaft retart your problem would be dead/bad camshaft sensor or wiring or plug-in

The truck (when I put the new distributor in) ran fine that day that I posted....but the problem here is the truck runs fine and then doesn't and then does...it is an intermittent problem. I did not have the MODIS computer when I did it the first time.

I'm going to check my wiring and re-check the distributor. Place it on TDC and then see if th rotor button is pointed towards the pointer on the distributor body. If it is not I will make sure it is and then recheck the camshaft retard setting to see how close it is to zero. Tks

The truck (when I put the new distributor in) ran fine that day that I posted....but the problem here is the truck runs fine and then doesn't and then does...it is an intermittent problem. I did not have the MODIS computer when I did it the first time.

I'm going to check my wiring and re-check the distributor. Place it on TDC and then see if th rotor button is pointed towards the pointer on the distributor body. If it is not I will make sure it is and then recheck the camshaft retard setting to see how close it is to zero. Tks

If it is a come and go problem I would say you have a bad canshaft position sensr or wiring to it problem.

The actual dist position will not come an go unless hold down clamp is lose and even then it would no always go -25 degrees..
But is camshaft sensor drops out/quits it can go to -25 degrees camshaft retard.
Check the wiring to it and the wiring plugin to dist real close.
Good luck and let us know how it goes.

Well, this in another chapter of my problems with this 1997 C1500 truck that I have come to love......

After my last post I decided to check and see if the pointer was pointing at the right place. So, I once again took number one plug out and allowed the engine to blow my finger off the hole as my wife clicked the started holding my grandson Braden.

Once I aligned the harmonic harmonic balancer perfect with the TDC mark on the timing cover I went to work getting to the distributor. After taking the cap off I noticed that the rotor did not point directly at the arrow like it was supposed to. See pics. You can see by the pic from the radiator view that the rotor may be pointing at the arrow. But when you look at the picture from the air breather view you can see that is it off a bit.

Here is the fun part. There is NO ADJUSTMENT for the distributor. In the past you could loosen the bolt and rotate the distributor housing and you would achieve the correct static timing. But with this truck, the hold down is fixated to the distributor shaft and the small hole in the hold down does not allow for any left to right adjustment. This fine tuning will be left up to the electronics.

Having said that there is a way that you can pull the distributor up (and I did) and rotate the rotor portion to the next (advanced to the clockwise) tooth on the cam gear. This I did but now I was 1/4 to 1/2 inch on the other side of the arrow....Damn, starting to get frustrated. So, what happens when I get frustrated...I like to destroy things...ha. Took out my grinder and I round away one side of the hold down bracket so I could get some adjustment. Put the rotor back to the one-tooth-back position it was in the pictures and then I rotated the base until I achieved the proper alignment as shown in the last picture or as shown in 1 of the 3 I tried to post.

Took the truck for a drive and drove many stops and 10 miles or so and it ran perfectly and not one single miss did I detect. I'm not declaring it fixed but it just may be fixed. It sounded better, it idled just a bit lower, 750 or so vers 850,900. So far I think I may have done it after all the praying I've done.

The truck really didn't drive bad at all and I'm sure there are many out there that may not even have understood what I was talking about when I felt it miss..."Did you feel that?" said to a passenger..What? Well, I felt it and it was a miss....and now it seems not to be doing that and the service engine soon light has not come back on yet. Let's hope it stays off.

Thanks for your help MT.

Also notice in the last picture you can see not only correct allignment with the new distributor but you can also see how the hold down bracket is shifted to the right a bit and the bolt holding it seems to be squirting out the left side a bit.

Well, this in another chapter of my problems with this 1997 C1500 truck that I have come to love......

After my last post I decided to check and see if the pointer was pointing at the right place. So, I once again took number one plug out and allowed the engine to blow my finger off the hole as my wife clicked the started holding my grandson Braden.

Once I aligned the harmonic harmonic balancer perfect with the TDC mark on the timing cover I went to work getting to the distributor. After taking the cap off I noticed that the rotor did not point directly at the arrow like it was supposed to. See pics. You can see by the pic from the radiator view that the rotor may be pointing at the arrow. But when you look at the picture from the air breather view you can see that is it off a bit.

Here is the fun part. There is NO ADJUSTMENT for the distributor. In the past you could loosen the bolt and rotate the distributor housing and you would achieve the correct static timing. But with this truck, the hold down is fixated to the distributor shaft and the small hole in the hold down does not allow for any left to right adjustment. This fine tuning will be left up to the electronics.

Having said that there is a way that you can pull the distributor up (and I did) and rotate the rotor portion to the next (advanced to the clockwise) tooth on the cam gear. This I did but now I was 1/4 to 1/2 inch on the other side of the arrow....Damn, starting to get frustrated. So, what happens when I get frustrated...I like to destroy things...ha. Took out my grinder and I round away one side of the hold down bracket so I could get some adjustment. Put the rotor back to the one-tooth-back position it was in the pictures and then I rotated the base until I achieved the proper alignment as shown in the last picture or as shown in 1 of the 3 I tried to post.

Took the truck for a drive and drove many stops and 10 miles or so and it ran perfectly and not one single miss did I detect. I'm not declaring it fixed but it just may be fixed. It sounded better, it idled just a bit lower, 750 or so vers 850,900. So far I think I may have done it after all the praying I've done.

The truck really didn't drive bad at all and I'm sure there are many out there that may not even have understood what I was talking about when I felt it miss..."Did you feel that?" said to a passenger..What? Well, I felt it and it was a miss....and now it seems not to be doing that and the service engine soon light has not come back on yet. Let's hope it stays off.

Thanks for your help MT.

Also notice in the last picture you can see not only correct alignment with the new distributor but you can also see how the hold down bracket is shifted to the right a bit and the bolt holding it seems to be squirting out the left side a bit.

You are welcome.
Also glad to see you are understanding getting the dist setting set.
And saying a prayer and asing for God's help does help.
I have saw and witnessed it many times.

On setting the dist besides getting it On TDC compression at the timing mark I always confirm the timing pointer is right on the money.
Sometimes they are off.
I use a soft feeler tool an reach in the spark plug hole and feel for piston TDC.

After confirming true TDC and the dist rotor setting is close but off.
If moving the dist one tooth does not help.
As you have figured out if and done slotting the hold down clamp will usually bring it in.
But only if it is close say around 5-10 degrees off.

If off in the 15 degree range I have run into having to turn the dist gear on the dist shaft a half turn 190 degrees.
The dist gear roll pin hole is a little off set and turning it a haft turn changes the rotor position in the - or + 10 degree range.
Also some after market dist caps will throw things off a few degrees.

Back to your running good now and no miss or codes you are right on the money or close on camshaft retard.

To see where it is set it now need to be put on a scanner and get the camshaft retard readout.
And if off over 1-2 degrees try to bring it back into 0 degrees or as close as you can get it.
Let use know how things goes.
Good luck
Replacement dist or motor change can cause you to have to do that.


Also

Didn't think about the roll pin thing but I bet you that is a problem as some "rebuilt" distributors may not get it in right. I bet if I were to do that, that I may get it to line up right on the nose without having to modify the hold down.

Silly design anyway to have it fixated at the hold down like they did. There almost always will need to be some slight adjustment.

Tks

I may or may not even put it on the computer but I am wondering how this change for the better will affect my gas mileage as before I was getting really no better than my son's 350 Silverado.

Greg