I have a 94 Chevy 3500 Crew Cab with a 6.5 TD. It's my "Country Cadillac". I love my truck but it's been quite a while since I have driven it because I don't feel like I can trust it.

The truck has always had a very sensitive accelerator pedal but it started surging when driving it to my daughters 1 night. It is worse at 55-60 mph and a low speeds of around 25. I can't get it to hold a steady speed at all. It will surge and let up, surge and let up. It gradually gains speed because it does not let up long enough for the speed to drop back completely.

It has been starting and running good at idle (husband has been starting it every little bit just so it doesn't sit too long without running) but it has now started intermittently running rough at idle until it warms up completely. My husband has noticed at idle the OP gauge bounces back and forth between 40 & 60 lbs. The other day he gave it a little fuel at idle to see if it would smooth out but it revved more than the pedal he gave it. He immediately released the pedal but would not slow down. He had to shut it off like that which is not good!

Truck is also blowing more black smoke when you accelerate.

Just a few months before it started doing this, We had a problem with it dying just driving down the road. It would usually start right back up but sometimes we had to wait a few minutes. Finally would not start when we got in it to go somewhere. We were told it was probably the PMD causing the problem, so we bought a new one with remote harness.
We also replaced the fuel cut off switch. This seemed to cure the problem and for several months it ran fine. Then this surging started.

My husband has cleaned and tightened all grounds and checked all electrical connections. We also tried changing the APPS. It made no difference. I have been reading posts on this forum from people who are having similar problems although not exactly the same. I see a lot of people being told that to the OPS. Does this sound like it could be caused by the OPS. I do know that several years ago we did have to change the OPS but the symptoms were not the same.

Sorry to be so long winded but I figured it might help if you had as much info as possible.

Thanks for reading! Any help greatly appreciated!

 

Have you pulled codes yet there are more than likely codes knowing these will help with diagnosing any problems with said truck And when you replaced the PMD did you put it on a heat sink and where is PMD located now??

 

No have not pulled codes. Will try to do that today. It does not kick any lights on though.

 

Just because the SES light is not comming on dont mean that there are not codes present

 

x2. some codes do not trigger the SES light

 

PMD failure,or IP giving up-start with a new PMD and remote mount it on a heatsink outside the engine bay,kits are available from many vendors -shop around and weigh price against warranty.

 

My husband took the truck up to the auto parts and ran the codes but none showing. A few days later, after he drove the truck up to the auto parts store, he went out to start it and let it run for a little bit. When he started the truck it would no longer idle like it should. It is now idling at 2,000 rpms. He has started it a couple of times since then and it starts fine but idles at 2,000.

Any ideas??

 

Same thing I posted above.

 

This is exactly what my truck is doing presently with the only exception being that it still idles at normal RPM's for the moment. Did you ever come up with a remedy for your troubles. I really miss my good running truck someone please help. I have already relocated he PCM and changed the oil pressure sensor, lift pump, and APPS.

 

Hi
You have got an air leak in the fuel system check all pipes connections bleed system
When a small amount of air enters fuel system it will surge then go back to normal