1996 GMC C3500 Timing, rich smell and performance

ONAWAVE

MEMBER
1996 GMC C3500
V8
4WD
AUTOMATIC
117,000 MILES

Still love my old dog dually GMC. I'm not a diesel man, so I'm keeping my 96 7.4L vortec. I pull a 13k trailer with it, and lately when I'm going up hills the service engine soon light comes on. It also smells like it's running very rich. (you can smell the raw gas).

I took it to a shop and they said the code was the timing was off. They re-timed it. The very next time I towed with it going up hill again the service engine soon light came on. The light went off before I could take it to a shop and have it tested. (about the 3rd time I drove it with out the trailer). It still smells like it's running rich, and gas mileage is about 8 mpg.

Truck is total stock, and all original (but I have replaced spark plug wires, cap, rotor and so on). I have two questions 1. What will cause the rich smell, and the service engine soon light to come on while towing up hill, and then go off once I'm not towing..

And 2.. What kind of no B.S performance upgrades can I do. Exhaust, TBI spacer, computer chip?? (I do NOT WANT to put headers on this truck). I just want this truck to run another awesome 117k miles for me.

Thanks, Paul

1 Reply

DR LOOT

MECHANIC
2,311 POSTS

To answer your first question 1. What will cause the rich smell, and the service engine soon light to come on while towing up hill, and then go off once I'm not towing.. it could be several issues:
1. Your TBI injectors are malfunctioning caused by a plausible debris in the fuel system, have you checked their spray pattern to make sure they are equal? check your fuel pressure make sure it is correct and replace the injectors. Before the truck starts on fire like mine DID!!!!
2. The reason the service engine light is coming on is because you're having to give it lots of all throttle, and the engine is flooding therefore the computer is detecting a malfunction causing the engine light to come on momentarily, once the issue is corrected the computer readjusts and the engine light shuts off

to answer your second question:
2.. What kind of no B.S performance upgrades can I do. Exhaust, TBI spacer, computer chip?? (I do NOT WANT to put headers on this truck). I just want this truck to run another awesome 117k miles for me.
1. you could install an RV cam, replace the intake manifold with a performer, get an aftermarket TBI with an upgraded computer, but you would just be wasting your time trying to make a gas engine perform like a diesel, Get It?
I hope this information helps you if you have anything else to add let me know, now I will show you my truck and yes it is a diesel, but it will tow anything out of anywhere