1994 1500 5.7 Liter Engine Skipping/misfiring

bkwalker · #1 12-18-2005, 09:22 PM

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.

horse482 · #2 12-20-2005, 04:35 PM

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.

bkwalker · #3 12-20-2005, 09:06 PM

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.

bkwalker · #4 12-26-2005, 09:36 PM

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?

jjrenner · #5 12-27-2005, 09:12 AM

Quote:

Originally Posted by bkwalker

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

bkwalker · #6 12-30-2005, 09:29 PM

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?

TEXAS-HOTROD · #7 12-30-2005, 09:46 PM

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.

zirb · #8 12-30-2005, 10:53 PM

Bump for future ref.

bkwalker · #9 07-26-2006, 12:47 PM

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.

I'm guessing it is something in the computer.

bkwalker · #10 01-24-2008, 12:08 PM

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

J-Ri · #11 01-24-2008, 04:11 PM

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.

bkwalker · #12 01-24-2008, 06:40 PM

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 cAT · #13 01-24-2008, 08:59 PM

Quote:

Originally Posted by 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..............

bkwalker · #14 01-25-2008, 11:23 AM

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

j cAT · #15 01-25-2008, 06:06 PM

Quote:

Originally Posted by 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......

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