92 K1500 problems/"gutless"

I have a 92 K1500 with the 5.0L, to start off I will tell everyone that yes I have performed all "normal" tests and checks on the pickup such as fuel pressure and tested sensors ect ect. and they are all within specifications. Anyway the pickup has 226k mile on it so its not new by any means but it is completely gutless. It has a hard time maintaining speeds of 60mph +. It seems powerless. A little history: the pickup has a rebuilt transmission, and i have replaced several parts such as the TPS, Coolant sensor, fuel pump, thermostat, cap, rotor, spark plugs, wires, it has no catylatic converter and true dual exaust with glass packs, a rebuilt throttle body, and several other things have been replaced too. After replacing all of those things the problem still exists.

The symptoms I am getting include lack of power, hard starting, hesitation during exceleration, a "dead spot" in my throttle response, as well as rough idle(when i say rough idle i mean during driving when you excelerate then let off of it it chugs a couple of times then idles back out smooth). It also has low oil pressure and this problem just arose its not so low that its dangerous but it is lower than normal. Also even after replacing the thermostat and coolant temp sensor the gauge in the pickup acts wierd. It will fluctuate between the 1/4 and 1/2 mark constantly.

I am at a loss here of why my pickup could be acting the way it is. I know the 305 doesnt have the power a 350 does but it still shouldnt be as gutless as it is. Any ideas as to what the actual problem could possibly be?

I have a 92 K1500 with the 5.0L, to start off I will tell everyone that yes I have performed all "normal" tests and checks on the pickup such as fuel pressure and tested sensors ect ect. and they are all within specifications. Anyway the pickup has 226k mile on it so its not new by any means but it is completely gutless. It has a hard time maintaining speeds of 60mph +. It seems powerless. A little history: the pickup has a rebuilt transmission, and i have replaced several parts such as the TPS, Coolant sensor, fuel pump, thermostat, cap, rotor, spark plugs, wires, it has no catylatic converter and true dual exaust with glass packs, a rebuilt throttle body, and several other things have been replaced too. After replacing all of those things the problem still exists.

The symptoms I am getting include lack of power, hard starting, hesitation during exceleration, a "dead spot" in my throttle response, as well as rough idle(when i say rough idle i mean during driving when you excelerate then let off of it it chugs a couple of times then idles back out smooth). It also has low oil pressure and this problem just arose its not so low that its dangerous but it is lower than normal. Also even after replacing the thermostat and coolant temp sensor the gauge in the pickup acts wierd. It will fluctuate between the 1/4 and 1/2 mark constantly.

I am at a loss here of why my pickup could be acting the way it is. I know the 305 doesnt have the power a 350 does but it still shouldnt be as gutless as it is. Any ideas as to what the actual problem could possibly be?

What are the fuel pressure readings with the ggauge?

When was last tune up??

Any codes?

I cant recall the exact fuel pressures sorry. I did the test when i put in the new fuel pump and filter(old fuel pump quit) which was a while back, but I know they were all right about where they should be and within the normal chevy specs.

I just did a tune up on it about a month and a half ago like said in the post above; put in cap, rotor, wires, and new spark plugs. As well as a total rebuild of the throttle body. It made no significant difference.

As far as codes go it has given me a code 43 a few times(I believe the primary reason for the code is ICM low voltage.) But the last time I got that code was close to 6 months ago and it was cleared and hasnt came up again.

I have cleaned and looked over the IAC and the EGR valves and they seem to be ok and working fine. So im not sure what it could be from. I do know that it is running pretty rich(A while back had it hooked up to a scanner that shows live data and said it was running rich.) it smells strongly of gas(partly because it has no catalytic converter but even so it shouldnt be smelling as bad as it is. Could that be an oxygen sensor issue?

The temp gauge fluctuating indicates air in the cooling system.

Have you checked the "base" timing? Any vacuum leaks? Spark plug coloring?

There are so many possibilities that it boggles the mind.

Compression test?

Leakdown test?

Weak coil?

Plugged fuel filter/defective fuel pump?

Contaminated gasoline?

Partially-plugged or leaking injector(s)?

EGR leaking into intake manifold

Vacuum leak to MAP sensor

Plugged air filter

The list goes on and on.

We haven't even gotten to verifying sensors one-by-one using proper procedure. You say you've already done some diagnosis, but did you do it correctly? I get the sense that this is somewhat new to you.

The temp gauge fluctuating indicates air in the cooling system.

Have you checked the "base" timing? Any vacuum leaks? Spark plug coloring?

There are so many possibilities that it boggles the mind.

Compression test?

Leakdown test?

Weak coil?

Plugged fuel filter/defective fuel pump?

Contaminated gasoline?

Partially-plugged or leaking injector(s)?

EGR leaking into intake manifold

Vacuum leak to MAP sensor

Plugged air filter

The list goes on and on.

We haven't even gotten to verifying sensors one-by-one using proper procedure. You say you've already done some diagnosis, but did you do it correctly? I get the sense that this is somewhat new to you.

Ok thank you for the replies, How do i fix the air in the cooling system issue? Also base timing has been check and re timed and no improvement was seen. When I changed the spark plugs the old ones were a brownish red color almost like the color of red dirt.

As far as the diagnoses goes I can say i probably havent done it correctly sorry. I know my way around an engine pretty good and have been a mechanic for 3 years but I have been a mechanic on a farm for 3 years. The "farm way" and the right way are two different things usually as far as testing and diagnoses goes. So I am willing to learn the right way and take any help I can get i just would prefer to spend as little money as possible on diagnoses tools. What all would be needed for the right way?

Compression test- Havent done one, know i need to though

Leakdown test- Havent done one

Weak coil- the possibility of this being the problem has crossed my mind but how do you test it? Is there any way of doing it with out an amp meter?

Fuel pump/filter- both of those components have been replaced and performance was the same before and after.

Contaminated gasoline- Problem has been on going for several months so i think this can be ruled out.

Injectors leaking or plugged- I rebuilt the throttle body and cleaned it as well as put a new adjustable fuel pressure regulator in it. So I dont think this could be the problem but how would i check for sure?

EGR leaking- How would i check to see if this could be the problem?

Vacuum leak to MAP- I dont think its that I took the vacuum line that goes to the MAP and put my thumb on one end and sucked on the other and it held vacuum. I still might as well check the correct way though so how do I do that?

Plugged air filter- not this have an aftermarked "K&N" style filter and just cleaned and re oiled it. I have been told though that these type of filters are actually worse than the stock one because they are sucking in hot air into the engine instead of cold so I am considering putting the stock system back into use after a few modifications(taking baffles and what not out) to the intake tube to help it "breath" better.

Ok thank you for the replies, How do i fix the air in the cooling system issue? Also base timing has been check and re timed and no improvement was seen. When I changed the spark plugs the old ones were a brownish red color almost like the color of red dirt.

As far as the diagnoses goes I can say i probably havent done it correctly sorry. I know my way around an engine pretty good and have been a mechanic for 3 years but I have been a mechanic on a farm for 3 years. The "farm way" and the right way are two different things usually as far as testing and diagnoses goes. So I am willing to learn the right way and take any help I can get i just would prefer to spend as little money as possible on diagnoses tools. What all would be needed for the right way?

Compression test- Havent done one, know i need to though

Leakdown test- Havent done one

Weak coil- the possibility of this being the problem has crossed my mind but how do you test it? Is there any way of doing it with out an amp meter?

Fuel pump/filter- both of those components have been replaced and performance was the same before and after.

Contaminated gasoline- Problem has been on going for several months so i think this can be ruled out.

Injectors leaking or plugged- I rebuilt the throttle body and cleaned it as well as put a new adjustable fuel pressure regulator in it. So I dont think this could be the problem but how would i check for sure?

EGR leaking- How would i check to see if this could be the problem?

Vacuum leak to MAP- I dont think its that I took the vacuum line that goes to the MAP and put my thumb on one end and sucked on the other and it held vacuum. I still might as well check the correct way though so how do I do that?

Plugged air filter- not this have an aftermarked "K&N" style filter and just cleaned and re oiled it. I have been told though that these type of filters are actually worse than the stock one because they are sucking in hot air into the engine instead of cold so I am considering putting the stock system back into use after a few modifications(taking baffles and what not out) to the intake tube to help it "breath" better.

When was the K&N filter system installed before the issue or since the issue???

Ok thank you for the replies, How do i fix the air in the cooling system issue?
It's a pickup. Radiator cap is probably the highest point of the cooling system. Pull the cap off. If the radiator is full to the top--you don't have air in the cooling system.

When I changed the spark plugs the old ones were a brownish red color almost like the color of red dirt.
Gasoline additives. I've seen red, green, yellow, brown. Sometimes multiple colors on the same plug. But if it's not additives...it's contamination.

i just would prefer to spend as little money as possible on diagnoses tools. What all would be needed for the right way?
The right tools. Or a repair shop to do it for you.

Compression test- Havent done one, know i need to though
OK.

Leakdown test- Havent done one
Leakdown tester and a KNOWN GOOD ENGINE or thirty. Use the tester on as many "good" engines as you can, then test your pickup. The indicated leakage is as much a result of the leakdown tester as it is the actual cylinder leakage. SOME gauges indicate 10% leakage, and the cylinder is shot. SOME gauges indicate 40% leakage, and the cylinder is fine. Until you know how YOUR gauge responds, the percentage means NOTHING unless you hear air coming from the intake (intake valve leakage) or the exhaust (exhaust valve leakage) or see/hear air in the cooling system (cracked casting or defective gasket) ALL engines will have some leakage past the rings.

Weak coil- the possibility of this being the problem has crossed my mind but how do you test it? Is there any way of doing it with out an amp meter?
Is there any way to do it WITH an ammeter? You're looking for voltage, not amperage. Use a $12 spark tester like the one on the left--HEI style. Center electrode is recessed into the porcelain to make for a larger gap.
http://www.chevelles.com/techref/hei_files/image012.jpg

http://www.chevelles.com/techref/hei_files/image014.jpg

If your ignition will reliably make sparks at the coil tester, the coil probably isn't defective.

Fuel pump/filter- both of those components have been replaced and performance was the same before and after.
Does the pump get 13+ volts WHEN RUNNING and tested AT THE FUEL SENDING UNIT? If the wiring to the pump is corroded, the pump won't run at full speed. Very common for the fuel pump relay to corrode internally, or for the ground wire to corrode at the frame rail. Bad wiring anywhere in the circuit will be a problem. THIS is where you need the ammeter.

It's almost guaranteed that the original wiring at the fuel sending unit is burned up. (INSIDE the fuel tank) Most fuel pumps come with a repair harness to correct the problem. DID YOU INSTALL the fresh wiring?

Contaminated gasoline- Problem has been on going for several months so i think this can be ruled out.
Are you filling the truck from the same "Farm Tank" that maybe has water in it? Twenty gallons of pesticide got dumped in "by mistake"?

Injectors leaking or plugged- I rebuilt the throttle body and cleaned it as well as put a new adjustable fuel pressure regulator in it. So I dont think this could be the problem but how would i check for sure?
I'm told a timing light will "freeze" the spray pattern enough to check for a nice cone-shape and fine droplets.

EGR leaking- How would i check to see if this could be the problem?
Open the valve by hand, see if the idle changes. Some trucks use positive or negative back-pressure style EGR valves, and opening by hand won't truly open the valve. Might have to remove and visually inspect.

Vacuum leak to MAP- I dont think its that I took the vacuum line that goes to the MAP and put my thumb on one end and sucked on the other and it held vacuum. I still might as well check the correct way though so how do I do that?
Suck on the vacuum hose while you watch the voltage change on the scan tool or voltmeter.

Plugged air filter- not this have an aftermarked "K&N" style filter and just cleaned and re oiled it.
If it didn't have an eighth of an inch of dirt on it, you wasted your time. K&N filters are damaged by over-cleaning; almost nobody leaves them alone long enough for them to truly NEED cleaning. For the most part, cleaning an oiled-gauze type filter is the worst thing you can do to it.

I have been told though that these type of filters are actually worse than the stock one because they are sucking in hot air into the engine instead of cold so I am considering putting the stock system back into use after a few modifications(taking baffles and what not out) to the intake tube to help it "breath" better.
It does not need to breathe better. It needs a cold-air intake to reduce detonation. Put it back to stock and leave it alone.

Lots of good info Hunter, your symptoms almost mirror mine and I had E.G.R. problems. What weight oil do you use? Do you change the oil regularly? What gear ratio?

Thanks everyone you have helped a pretty good ammount! Any other ideas or suggestions as to what it could be? Anything at all?

James: I use 10W 40 oil in it, change it every 3k miles, and gear ratio is 3.43

since the exhaust is wide open no restrictions , I would say the cam lobes are worn and the compression is low. no sucking no power.

engines are like pumps. when they lose compression they no longer can suck air and fuel to create power.

you most likely will find low vacuum as well.

305 is a gutless engine . when used in a truck at this mileage I am suprised it still can climb a hill.

1992 truck is a heavy vehicle.

Hunter, nothing wrong with 10-40. That's what i ran in mine when I had it for many, many years. Mine also had 3.43 gears I made the mistake of going with oversized tire and wheels and killed my power, well live and learn you know? Good luck.

Thanks everyone you have helped a pretty good ammount! Any other ideas or suggestions as to what it could be? Anything at all?

James: I use 10W 40 oil in it, change it every 3k miles, and gear ratio is 3.43


your not supposed to use 10-40wt oil.

gm stated back in the 80's not to use this wt oil. causes high wear.

10-30wt is what to use. I guess that also is a good reason for your power issue.

your not supposed to use 10-40wt oil.

gm stated back in the 80's not to use this wt oil.
True. GM does not recommend 10W40.

I always figured it was a marketing scheme; they were introducing "Goodwrench" motor oil about that same time, and I figured they were pushing people to use the "House brand".



10-30wt is what to use. I guess that also is a good reason for your power issue.
Ehhh...not so much. I don't think any other manufacturer are as allergic to 10-40 as GM; it seems to work for the other carmakers. 'Course, now everyone is pushing the 5-30 or 0-20 based on "fuel economy".



Good call on the vacuum gauge; it'd be interesting to see what the cranking and idling vacuum of that truck is.

on my 1983 GM vehicle I used castrol 10-30wt. changed oil at 3500mi. used ac filters. the engine did not use much oil . down 1/2 qt between oil changes , at the 380,ooo mi when I sold it. the emissions tests showed it performed better than many much newer vehicles. it was 17yrs old at that time. first guy to look at it buys it. one month later he totals it.

I did have a large tranny cooler on it. that most likely is why I never did any engine or transmission repairs.

I used 10-40 on my 1992 purchased new until I sold it two years ago with never a problem. I sold it to my nephew and he drives it everyday and uses 10-40 Lubro-Moly anti Friction. The 305 was o.k. in that truck but I went with oversize tires and rims that killed power and gas mileage. 10-30 is o.k. though but I never thought going up one weight was bad.

I used 10-40 on my 1992 purchased new until I sold it two years ago with never a problem. I sold it to my nephew and he drives it everyday and uses 10-40 Lubro-Moly anti Friction. The 305 was o.k. in that truck but I went with oversize tires and rims that killed power and gas mileage. 10-30 is o.k. though but I never thought going up one weight was bad.

back in the mid 80's and before that , 10-40wt was used most often. then GM came out with the news of high wear/lack of proper lubrication with this used in their engines. so I had to believe it then and would say in the 305cu I still own no wear issues and the other 1983 I sold , had no engine issues as well.

since the exhaust is wide open no restrictions , I would say the cam lobes are worn and the compression is low. no sucking no power.

engines are like pumps. when they lose compression they no longer can suck air and fuel to create power.

you most likely will find low vacuum as well.

305 is a gutless engine . when used in a truck at this mileage I am suprised it still can climb a hill.

1992 truck is a heavy vehicle.

I have considered that because it is old and has high mileage and the "chug" I get after accerlerating and then letting off resembles a hot rod engine with a low cam at idle(like when it lopes) So trust me i have thought of cam issues and the fact that the engine it just plain worn out but what leads me away from thinking that are these things; the engine burns less than 1/4 quart of oil between changes, it ocasionally runs like a raped ape and has all sorts of power and acceleration(very rarely but sometimes it happens just out of the blue) as well as after i put my stock air intake back on after modifying it and making it free of restrictions (so its a free flowing true cold air intake) it does seem to run better and downshift less frequent at higher speeds.

Those things lead me to believe that the issue lies somewhere other than a "worn out engine" I have also considered the fact that the problem could lie in the drivetrain. It does have a rebuilt transmission and a new torque converter but the transfer case is not in the best shape(it takes a little while for 4 wheel drive to actually engage and sometimes you can hear a clanking sound when shifting from park to OD, it was also driven without oil in the transfer case for a couple hundred mile by the previous owner I am kinda just limping it along till i absolutely have to get a new one) as well as the rear diff isnt new either so that has crossed my mind It could be any of those things, and even thought the torque converter is new sometimes i do think thats my problem it acts like the torque converter is the wrong rmp stall for the engine.

Is it possible that it could be drivetrain related or is that a crazy thought?....I realize i need to do the test stated in the previous posts but i wont have time to do so till this weekend so any more info i can get to help me and help pinpoint is greatly appreciated.

well this just adds to my belief that this is worn engine.

the 305 has a very restictive intake to the combustion chambers from day one. the cold air intake, when used in the warm air temps does greatly improve power output of this engine.

if the vehicle must down shift to maintain speed going up slight grades at hywy speed indicates insufficent power. the transmission gets damaged from this .

when the cam wears out the valves do not travel as much as they should this reduces intake of the fuel air mixture.

gradual loss of power with wear issues you have no idea how it should be with a 305 that had the spec HP ability. you get used to and drive the vehicle to compensate.

all thats needed is a compression check.

one possility is the compression rings maybe carboned up. thinking about your problem I did see this a long time ago. fuel used in the 80's had nasty additives that created carbon on these rings.I use and still use today marvel mystery oil to the fuel to help remove these deposits and lube the rings . another product called regain by gumout works good to quickly remove combustion chamber deposits.

the egr if it has over 150,ooo mi on it should be replaced. too much EGR adds carbon to the combustion chamber. any EGR thats over 10yrs old also is in need of replacement. diaphram issues.

Oil consumption is not bad at all and The engine seems well maintained. I use Marvel Mystery Oil regularly and Gumout Regane also, I believe these additives help. Torque converters are important to engine performance, I would check out the egr system further as well since sometimes performance is great. Good luck and lots of good information here.

I will definitely try to do a compression test this weekend at the very least, hopefully check my vacuum too! I will let you know the findings. I will also look into the EGR and replacing it. I have a 350 with only about 63k miles on it in another pickup with a blown head gasket(this summer once it warms up i plan on putting a new head gasket in her and putting that engine in the pickup we are currently talking about) So for the time being I will see if I can swap out the EGR valves and see how much of a difference it makes.