On and off problem...

[Terry Packman]

New here and I need help. I have a 94 K1500 5.7. The engine was replaced at 38k with a crate motor. Truck was a farm truck until my brother in law picked it up at 110K. I got it from him at 130k and it ran strong. I started getting some really rough hesitation under load and sometimes at idle. I did not have the time or place to work on it in sub zero weather so I took it in. Code 43 (electronic Spark Control) was flashing and the Chevy dealer found a knock sensor wire that had been knicked in two, so replaced the sensor and connector, and the EGR was not holding vacuum so replaced that also. Map Sensor was replaced about two months ago and I replaced the distributor and rotor at that time. Plugs and wires were good. NO CODES are flashing and it runs strong, but every other day it seems as though the same problem occurs. It starts and idles fine, I pull out and go down the road and come to a stop and the idle drops or it hesitates big time off the line. If I drop it into just drive instead of overdrive it seems to run better while its doing this but it still hesitates. If I don't keep the rpms up a bit it will sometimes die but it starts right back up and continues to run rough or hesitate off the line. When I get to where I am going if I stop to back in it dies, it starts a bit hard and then runs rough and as soon as I drop it into gear it stalls, after about four or five times it starts and runs rough but then I can go. The times it runs strong there is no hesitation at all and it will smoke the tires off. It does not matter what temp it is but it does seem worse the colder it is. I replaced the fuel filter last week and emptied some gas into a cup and there was no water in the fuel. I am thinking it is either a fuel pump issue or the ECM is going bad. Any other ideas on what it could be?

 

[Fimpen]

Exact the same problem I have with my 1990 c2500 350 TBI. I have changed pretty much everything you have, but I also did the fuel pump a few weeks ago. Did not help.

I have tried to troubleshoot it a few times. The last time I was in the garage, I noticed that the idle starts to wander when I hold the brake pedal down (warm engine, in gear). And when I hold down the brake pedal and give it some gas the truck wants to die. So I think that it might be connected to the brake-system in some way. I have still no solution to this..

 

[RichLo]

vacuum leak in the brake booster?

 

[Terry Packman]

Exact the same problem I have with my 1990 c2500 350 TBI. I have changed pretty much everything you have, but I also did the fuel pump a few weeks ago. Did not help.

I have tried to troubleshoot it a few times. The last time I was in the garage, I noticed that the idle starts to wander when I hold the brake pedal down (warm engine, in gear). And when I hold down the brake pedal and give it some gas the truck wants to die. So I think that it might be connected to the brake-system in some way. I have still no solution to this..

Talked with a buddy of mine that was a mechanic for a few years and now teaches. He stated that it could be a torque convertor problem. Not engaging and releasing properly. He said you can test it through the ecm. He stated that when you take off it is not fully engaging and when under load it is not fully releasing and engaging. This could explain the stalling under load and no power at times. I will let you know. With no garage it will be next week before its warm enough to test out.

 

[98chevy2500SS]

Roughness, kind of sounds like a fuel injector problem. My truck had this issue when I bought it, had 137k miles on it. When it idled, it idled poorly. After driving it, when I put it in park, it would die instantly, even when warm. After my dad and I replaced the fuel injector spider on it, ran like it came out of the factory. Now mind you this is a Vortec that I am talking about, I am not much of a TBI guy, but this sounds like a fuel injector issue to me. It may even be a fuel pump issue, but I am leaning towards fuel injector problem. Like I said, I'm not much of a TBI guy, but it would be something to check into if your fuel injectors are doing ok.

 

[Tom P]

I'd say test your fuel pressure first. You can usually rent a fuel pressure test kit from a local auto parts store. It sounds like you are having a similar issue to what I was having with my truck although my truck wouldn't die. I had very low fuel pressure. Replaced the pump and it solved all my woes. I've heard of chafed injector wires causing all kinds of fuel problems. Also It will be a good indicator if you run the truck with the air cleaner off to see what kind of fuel spray pattern you have.

 

[mountie]

Check out your TPS ( Throttle Position Sensor)... that can drive you nuts if not working correctly.

 

[Terry Packman]

Okay...problem is fixed or I should say several problems at once. Since I could not work on it because of weather and not being able to fit in the garage I took it in to our local chevy dealer. They basically threw parts at it and called it good. They supposedly did a fuel pressure test and said it was fine and they supposedly checked the whole vehicle over. Come to find out they did not check anything, talked with a buddy of mine (sales) who works there and he stated the guy who worked on my truck turns wrenches about as well as a first grader and they have had several problems with him. So I took it somewhere else and it turns out it was the fuel pump, something that had supposedly been checked. In addition I have a bad water pump. Next time I trust my own instincts and do it myself...buying one of those temp vehicle storage tents and will put it up in my yard...would have saved about $500. Thanks for all the suggestions!