1994 1500 5.7 Liter Engine Skipping/misfiring

My truck is skipping but if I give it more throttle it will stop but then will start back when I let off the throttle. It seems like it is only running on half the cylinders. This problem is intermittent which makes it very hard to troubleshoot even for the dealership and other places I have taken it. Also, the problem is temperature sensitive. It only does it below 40 deg. F. Truck runs fine any other time of the year. Truck has new plugs, plug wires, distributor, egr valve, O2 sensor. Also, the IAC has been cleaned. The check engine light does not come on. I hope someone can help me. This is getting rather frustrating and expensive.

My 1994 GMC K1500 5.7 did the samething, I replaced the distributor with a reman. and it still didn't fix the problem, I took my truck to the local gm dealer, they pulled the dist. and tested, the reman was built different from the oem, the top of the shaft where the rotor sits was rounded and the rotor when cold would woble. Bought a new gm dist. (ouch) and that fixed most of the problem. Still had a slight miss. I had put new denso plugs in, of corse the dealer recommended acdelco, still same problem. I read a forum here and someone had talked about using an after market coil. They recommended a accell coil, I used an msd blaster coil, direct fit replacement. Solved my problems. I hope this helps you also. Good Luck.

Thanks for the information! Let me throw out some more details. Engine is totally stock with 172,000 miles on it. The distributor and EGR valve was replaced by the Chevrolet dealership (I agree, ouch) so I know they are good. They were just throwing parts at it trying to fix it, all the while I'm paying the bill! Looks like the accel ignition coil you were talking about is about $50 at my local auto parts store. So, I think it is worth a try. It's got to be something electrical if it's only acting up when its cold. I will post another reply when I get it installed. Thanks again.

Here is my update. I installed the new accel coil this evening. I had my fingers crossed. But, my hopes were dashed. This did not fix it. So, I will probably take it to a mechanic again. Does anybody else have any advice for me?

Here is my update. I installed the new accel coil this evening. I had my fingers crossed. But, my hopes were dashed. This did not fix it. So, I will probably take it to a mechanic again. Does anybody else have any advice for me?

I posted this earlier:

I have a 1995 K1500 5.7L and it had a slight tap from the driver side. It gradually got worse and eventually impacted the engine performance. The symptoms included a lot of "misfiring" and sputtering above 20MPH. It sounded like a Model "T" and had no power.

It turned out to be the engine knock sensor was bad and the computer was retarding the timing to the point of misfire.

Hope you get it worked out!

JP

JP,
Thanks for the information. I have passed it on to the mechanic.

My problem will pretty much happen at any speed and I do not hear a slight tap from the drivers side. Did your check engine light ever come on? How did you troubleshoot this?

If it misses/surges at part throttle, my first guess would be an EGR problem. Try unplugging the vacuum line to the E. valve, drive it, and see what it does.

Bump for future ref.

Here is a belated update: I took the truck to an auto repair shop and they replaced the fuel pressure regulator which I am told is located on top of the throttle body. But, still no change and have the same problem. Truck has been running fine since warmer weather has been here a while. Guess I will have to wait till this winter again to start troubleshooting again.:banghead:

I'm guessing it is something in the computer.

I am back again and still having the same issues as stated above. I think I may try to change out the knock sensor. But, wouldn't the check engine light come on if the knock sensor is bad?

Also, how hard is it and what are the steps to replace this knock sensor?

I hope someone can help me. This is still very frustrating.

BKWalker

If it was the knock sensor, it would probably do it at all temperatures. I would look at the knock sensor data with a scan tool before replacing the sensor. Unplugging the sensor should make it run good (if that is the problem), but will more than likely set the check engine light.

If it has the "stove pipe" (the tube that goes from the exhaust heat shield to the air intake into a valve), check to make sure that is working. My truck runs like crap at idle if it is disconnected. My thermal vacuum valve was bad, so every winter I run a vacuum line off the intake manifold directly, every spring I disconnect and plug the hose. You could fix it, of course, but why pay for something when you can bypass it for free? :) Also look at the fuel injector spray pattern.

J-Ri,
Thanks for the reply. I forgot to mention that it will skip and misfire even after the engine comes up to temperature. I will try unplugging the knock sensor and see what happens. I'll post my results.

I had the air cleaner off today and it was still misfiring so the "stove pipe" is not the problem.

BKWalker

J-Ri,
Thanks for the reply. I forgot to mention that it will skip and misfire even after the engine comes up to temperature. I will try unplugging the knock sensor and see what happens. I'll post my results.

I had the air cleaner off today and it was still misfiring so the "stove pipe" is not the problem.

BKWalker
check the engine temp sensor this could be defective it is next to thermostat. now its cold check old sensor resistance , compare with new when at same temp before replacing......the exhaust manifold hot air to intake manifold pipe and mixing valve in air cleaner is working? as this could cause this type of problems at 40deg f..............

My truck is finally fixed!! Since it was screwing up on a constant basis I took it to a local mechanic this morning. After driving around and using his scanner and trying a new MAP sensor (which didn't fix it) it turned out to be a bad injector.

Thanks for all the help. I hope this thread will help someone out in the future.

BKWalker

My truck is finally fixed!! Since it was screwing up on a constant basis I took it to a local mechanic this morning. After driving around and using his scanner and trying a new MAP sensor (which didn't fix it) it turned out to be a bad injector.

Thanks for all the help. I hope this thread will help someone out in the future.

BKWalker
what was wrong with injector electrical or the internal injector plugged /worn......

what was wrong with injector electrical or the internal injector plugged /worn......

While we were trouble shooting, we noticed the driver's side injector on the throttle body was not spaying fuel like the passenger side. So, we swapped connectors and still the driver's side injector was not working. So, we replaced it and it fixed the problem. So, not sure exactly what was wrong internal to the injector.

I'm just so grateful that it's running right.:grinno:

I have a 1991 S10, i put a 1995 350 tbi in it i changed the tbi gasket and ever since then both of my injectors are ticking.

I have a 1991 S10, i put a 1995 350 tbi in it i changed the tbi gasket and ever since then both of my injectors are ticking.
Start a new thread instead of reviving one that's been dormant since 2008.

You do know that fuel injectors tick when they're triggered by the ECM...right?

Hey everyone, I have a 1995 chevy 3/4 ton 4X4 with a 5.7 in it, I had new exhaust put on it, and on the way home it started to backfire and sputter, so reading some of the like threads on here, I thought maybe my EGR valve was not working properly, I replaced it, and now it's even worse! anyone have any other ideas?

Start a new thread instead of reviving one that's been dormant
^^^^^ next time.


What is your fuel pressure? What does the data stream show when you connect your scan tool? I'd be especially interested in O2 voltage, short- and long-term fuel trim, O2 crosscounts, coolant temperature, and knock sensor activity.

Sorry it took so long to get back to you,But this a little more history on the truck, I bought this truck brand new, so been kind of my baby, The truck has 331,000 miles on it, so no spring chicken by no stretch... That being said, this is what i have done so far, I checked the compression, all cylinders are at 105-111 psi, but 7-8 are at 93,98 psi, replaced the fuel pump, it was on the weak side (6 psi)new plugs,cap,rotor,MAP senser,EGR valve,When I get home from work tomorrow, I will put my scanner on it and see if it tells me anything, but currently not throwing any codes?

The truck has 331,000 miles on it, so no spring chicken by no stretch... That being said, this is what i have done so far, I checked the compression, all cylinders are at 105-111 psi, but 7-8 are at 93,98 psi,
What is your altitude? 111 would be terrible around here. 93 is not the worst I've seen, but it's very low. With 300,000+ on the clock I'd be concerned about timing chain wear retarding the camshaft. That will also drop cranking compression.

replaced the fuel pump, it was on the weak side (6 psi)new plugs,cap,rotor,MAP senser,EGR valve,When I get home from work tomorrow, I will put my scanner on it and see if it tells me anything, but currently not throwing any codes?
How old is the O2 sensor? Any chance they damaged it when the new exhaust was installed?