97 Jimmy, Cylinder 1 Misfire

[mwaldrp]

So, my engine started running rough at idle last weekend and my SES light came on. The light also flashed occasionally. The engine runs rough until reaching about 15 mph and then smooths out. It begins running rough again after slowing back down. I suspected a misfire and had the codes read at the local parts store. This showed a misfire in cylinder 1 but in no other cylinders. Last night I pulled the spark plug wire off the plug to test if it had spark and was able to see a blue spark arc between the spark plug lead and a screwdriver. I then removed the spark plug from the engine and placed it into the end of the spark plug lead. I filled the plug opening in the engine with an old plug. I was not able to see spark between the two nodes of the spark plug I removed from cylinder 1. However a blue spark would arc from the plug to my screwdriver. Should I be able to see the spark between the two nodes of the plug? If so, replacing the plug should solve the problem. If not, what is the next diagnostic step? I have blue spark at the end of the spark plug wire which I believe indicates the wire and the distributor are functioning properly. What is the next potential cause of a misfire?

[MT-2500]

Originally Posted by mwaldrp

So, my engine started running rough at idle last weekend and my SES light came on. The light also flashed occasionally. The engine runs rough until reaching about 15 mph and then smooths out. It begins running rough again after slowing back down. I suspected a misfire and had the codes read at the local parts store. This showed a misfire in cylinder 1 but in no other cylinders. Last night I pulled the spark plug wire off the plug to test if it had spark and was able to see a blue spark arc between the spark plug lead and a screwdriver. I then removed the spark plug from the engine and placed it into the end of the spark plug lead. I filled the plug opening in the engine with an old plug. I was not able to see spark between the two nodes of the spark plug I removed from cylinder 1. However a blue spark would arc from the plug to my screwdriver. Should I be able to see the spark between the two nodes of the plug? If so, replacing the plug should solve the problem. If not, what is the next diagnostic step? I have blue spark at the end of the spark plug wire which I believe indicates the wire and the distributor are functioning properly. What is the next potential cause of a misfire?

Which side are you checking no 1 cylinder?
Drivers or passanger side?
What brand of plugs are in it.
Start with putting in a good set of AC delco plugs.

A plug can not be tested the way you are testing.
The only way to test a plug is under compression with engine running or with a plug tester that will put compression on the plug.

It takes more spark and a better plug to fire under compression.

If you have good spark and good plug and good fuel pressure and good injector pulse.
Next step is ckeck compression and check for vacumn leaks.

After feeding us a good set of AC-Delco plugs let us know how it goes.

[mwaldrp]

Originally Posted by MT-2500

Which side are you checking no 1 cylinder?
Drivers or passanger side?
What brand of plugs are in it.
Start with putting in a good set of AC delco plugs.

A plug can not be tested the way you are testing.
The only way to test a plug is under compression with engine running or with a plug tester that will put compression on the plug.

It takes more spark and a better plug to fire under compression.

If you have good spark and good plug and good fuel pressure and good injector pulse.
Next step is ckeck compression and check for vacumn leaks.

After feeding us a good set of AC-Delco plugs let us know how it goes.

This is the 4.3 L V6 engine so the No. 1 cylinder is farthest forward on the driver's side. (This is the easiest plug to reach...Hooray!)

The plugs in the engine now are E3 brand and they have raised my fuel economy significantly over the AC Delco plugs I had before. I do not know anything about the durability of the E3 plugs.

I tested the plug the way I did just to see if it was still conducting current. Are plug testers readily available? Could I borrow one from a parts store?

My next step was going to be to check for compression. However I have not checked for fuel pressure or injector pulse. The fact I am only having problems in one cylinder leads me to believe I have adequate fuel pressure but I don't know if this is a correct conclusion. How is injector pulse tested?

When I removed the plug, it did not seem to be wet with fuel. (This was shortly after running the engine for about 1/2 hour). Could this just be a clogged injector?

Thank you very much for your help MT-2500. You've patiently assisted me with a lot of problems and I greatly appreciate it.

[MT-2500]

Originally Posted by mwaldrp

This is the 4.3 L V6 engine so the No. 1 cylinder is farthest forward on the driver's side. (This is the easiest plug to reach...Hooray!)

The plugs in the engine now are E3 brand and they have raised my fuel economy significantly over the AC Del co plugs I had before. I do not know anything about the durability of the E plugs.

I tested the plug the way I did just to see if it was still conducting current. Are plug testers readily available? Could I borrow one from a parts store?

My next step was going to be to check for compression. However I have not checked for fuel pressure or injector pulse. The fact I am only having problems in one cylinder leads me to believe I have adequate fuel pressure but I don't know if this is a correct conclusion. How is injector pulse tested?

When I removed the plug, it did not seem to be wet with fuel. (This was shortly after running the engine for about 1/2 hour). Could this just be a clogged injector?

Thank you very much for your help MT-2500. You've patiently assisted me with a lot of problems and I greatly appreciate it.

You are welcome.
Always check fuel pressure for up to par.
Low fuel pressure can sometimes cause miss on on cylinder or weakest cylinder.
Injector pulse can be checked with a injector tester node light.
Most parts places have the injector tester.
I would not go for a clogged injector untill you have made sure every thing else is good.
The only was to check injector for being cloged or not working is with a engine caplable scanner with a injectror test built into it and a fuel pressure gauge hooked up.

Plug testers are almost a thing of the past.
Best and cheapest test is brand new plug installed and be done with wondering about or trying to test plug.
I used to use plug testers 45-50 years back when you cleaned and tested a lot of plugs.
And sometimes hooked the coil on it up under the front seat of a few peoples cars.
But when you could by plugs for 79 cents a plug people quit testing and just throw-ed old plugs away.
All except one old customer of mine.
He had a old oil fowler truck.
It would start to missing on 2-3 oil fouled plugs.
I would just pull old plug and put in 79 new 79 cent plug over paying a 1.00$ to get plug cleaned.
The customer would come by to pick up his truck and ask if I cleaned his plugs.
I would tell him no way 79 cents for new plug and a dollar to clean old plug.
Then he would go over to my trash can and pick out his old plugs and stick them in his pocket.
Then look at me and grin and say them plugs can be cleaned up.
And away he would go with his old plugs in his pocket a happy customer.
I always wonder if he actually had them cleaned and reused them.

But in your case I would drop the E3 plugs in trash can and get a good set of AC delco plugs.

Ac Delco plugs work best in GM cars and trucks and should give same mileage as E3 or BOSH or EKG.

To find out if it is plug or other thing switch plugs with a good firing cylinder or just put new plug in that cylinder.

On E3 getting better mileage was you checking mileage on the old worn out AC plugs before tune up or checking the mileage on new AC plugs after tune up?
The change to new plugs is what usually gives better mileage.
Let us know how it goes.

[mwaldrp]

Originally Posted by MT-2500

You are welcome.
Always check fuel pressure for up to par.
Low fuel pressure can sometimes cause miss on on cylinder or weakest cylinder.
Injector pulse can be checked with a injector tester node light.
Most parts places have the injector tester.
I would not go for a clogged injector untill you have made sure every thing else is good.
The only was to check injector for being cloged or not working is with a engine caplable scanner with a injectror test built into it and a fuel pressure gauge hooked up.

Plug testers are almost a thing of the past.
Best and cheapest test is brand new plug installed and be done with wondering about or trying to test plug.
I used to use plug testers 45-50 years back when you cleaned and tested a lot of plugs.
And sometimes hooked the coil on it up under the front seat of a few peoples cars.
But when you could by plugs for 79 cents a plug people quit testing and just throw-ed old plugs away.
All except one old customer of mine.
He had a old oil fowler truck.
It would start to missing on 2-3 oil fouled plugs.
I would just pull old plug and put in 79 new 79 cent plug over paying a 1.00$ to get plug cleaned.
The customer would come by to pick up his truck and ask if I cleaned his plugs.
I would tell him no way 79 cents for new plug and a dollar to clean old plug.
Then he would go over to my trash can and pick out his old plugs and stick them in his pocket.
Then look at me and grin and say them plugs can be cleaned up.
And away he would go with his old plugs in his pocket a happy customer.
I always wonder if he actually had them cleaned and reused them.

But in your case I would drop the E3 plugs in trash can and get a good set of AC delco plugs.

Ac Delco plugs work best in GM cars and trucks and should give same mileage as E3 or BOSH or EKG.

To find out if it is plug or other thing switch plugs with a good firing cylinder or just put new plug in that cylinder.

On E3 getting better mileage was you checking mileage on the old worn out AC plugs before tune up or checking the mileage on new AC plugs after tune up?
The change to new plugs is what usually gives better mileage.
Let us know how it goes.

So I'm going to replace plugs with AC Delco plugs to see if it fixes the problem, but if it doesn't I want to go ahead and test the fuel pressure to make sure that's not the problem. I will also be testing for compression in at least cylinder 1. What should the pressure reading be for the compression test?

I found this response you (MT-2500) gave to another poster having fuel pump problems and I have a few questions about it. My questions are in between the steps you recommended.

Hard to start cold or hot and fuel pressure testing guide lines.

Check cold start fuel pressure.

Should this be 64 to 65 psi for my engine? (1997, V6 4.3 L)

Check engine running fuel pressure.

Should this be 60 to 66 psi for my engine? (1997, V6 4.3 L)

Check engine running on the road fuel pressure.

Should this be 60 to 66 psi for my engine? (1997, V6 4.3 L)

Then shut it off and watch for fast leak down.

How much leak down in how much time is considered fast?

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.

Does 75 psi or higher indicate a good pump? (1997, V6 4.3 L)

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.

Could this happen on just one cylinder?

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.



Thanks again for your help.

[MT-2500]

Originally Posted by mwaldrp

So I'm going to replace plugs with AC Delco plugs to see if it fixes the problem, but if it doesn't I want to go ahead and test the fuel pressure to make sure that's not the problem. I will also be testing for compression in at least cylinder 1. What should the pressure reading be for the compression test?

I found this response you (MT-2500) gave to another poster having fuel pump problems and I have a few questions about it. My questions are in between the steps you recommended.

Hard to start cold or hot and fuel pressure testing guide lines.

Check cold start fuel pressure.

Should this be 64 to 65 psi for my engine? (1997, V6 4.3 L)

Check engine running fuel pressure.

Should this be 60 to 66 psi for my engine? (1997, V6 4.3 L)

Check engine running on the road fuel pressure.

Should this be 60 to 66 psi for my engine? (1997, V6 4.3 L)

Then shut it off and watch for fast leak down.

How much leak down in how much time is considered fast?

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.

Does 75 psi or higher indicate a good pump? (1997, V6 4.3 L)

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.

Could this happen on just one cylinder?

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.



Thanks again for your help.

On compression check.
Main thing is not to have over 10-15% varation between cylinders.
Anything over can cause miss or rough running engine.

When checking compression always block TBI buterfly open some.
If closed it can mess up compression check.
Compression can range from 150-200 lbs on most engines.
Best I remember yours may be around 175-185 lbs.

Fuel pressure specs for a 97 4.3 W or X engine is 60/66 lbs.

Full presure specs is up to 105 on a good Delphi pump.
That is one place Airtex fails test.

Your cold start pressure should be 64-65 lbs to squirt cold injector.
Cold start pressure affects all injectors.
Low engine running pressure can knock out a weak cylinder one or more.
key on engine prime up pressure should go to full pressure 65-66 lbs.
Engine running will range 62-65 depending on engine vacumn or load on engine.

I always like to check pressure on the road running and drive it 1/2 hr or more to get fuel pump warm up.

Leak down should be slow but do not remeber specs on that.
10 -15 lbs over 10 -20 minutes is not real bad but could be slower.
All thow a very fast leak down indicates a leak some place your engine starting and running is the main pressure to check and have up to par.

A lot of times fuel pressure tester gauges are off some.
Check with another gauge to make sure it is right.
A few lbs of is not good on the GM truck engines.

AC delco plugs are the way to go on GM engines.


Your are welcome and Good luck let us know how it goes.
MT

[mwaldrp]

I have an update on my misfire.

I haven't had a chance to get new AC Delco plugs yet due to work travel but this past weekend I took an old, worn AC Delco plug left over from my last tune up and put it in cylinder 1. The effect was immediate and impressive. I now have a smoothly running engine and have gone several days without a return of the SES light. I will replace all the plugs with new AC Delco plugs soon but it seems the problem has been solved. Thanks for the help!

[MT-2500]

Originally Posted by mwaldrp

I have an update on my misfire.

I haven't had a chance to get new AC Delco plugs yet due to work travel but this past weekend I took an old, worn AC Delco plug left over from my last tune up and put it in cylinder 1. The effect was immediate and impressive. I now have a smoothly running engine and have gone several days without a return of the SES light. I will replace all the plugs with new AC Delco plugs soon but it seems the problem has been solved. Thanks for the help!

You are welcome.
Glad you found the problem.

10-4 on the Ac-Delco plugs.

I just love the sound of Bosh and or E3 plugs hitting the trash can or being pitched back at the parts man that sold them to you.