I have a 91 2500hd with a 350 (5.7) and overdrive, has been a great work truck. I've built a few small blocks and I know quite a lot when it comes to motors. However, I and two other mechanics (shops, actuall buisinesses) can't figure this one out. It is getting about 5 to 6 miles to the gallon, when I accelerateit does fine at fist but if I push the gas a little farther it starts to stumble lossing power like its overloading. Before this started, within the past year it has a new timing chain, fuel pump, exhaust, complette tune up about two years ago. I've checked all sensors, pressure regulator and all seam to be fine. I also changed the temperture guage in the top of the intake that goes to the computer. I can see fuel folling of the butterfly valves at idle and have run three bottles of fuel injector cleaner at dubble strenght ( for up to 21 gallons, I use 9-10 gallons). Someone throw me a bone!

 

Have you taken a spark plug out and checked for a lean or rich condition?

 

91.......isnt that TBI? If so it sounds like a failed injector.......either way it goes it sounds like a failure in fuel regulation.

 

No I haven't checked the plugs but will. How do I check or know if a injector is bad. It seems to me if it was clogged it might loose power but would not get bad milage (5-6). seems like it is dumping fuel in the motor but there is no black or grey smoke. Could the coil not be putting out enough fire? Also, it is taking longer to start. I figure because it seems to be dumping gas and therefor not mixingwith the air properly. Is there anything I can try or check befor I go replacing injectors and regulator?

 

I the injector is leaking MORE fuel then it needs to then that explains the bad mileage....if it is a TBI.....remove the air cleaner and watch the injector with the engine running( a flash light shinning accross the fuel spray helps) you will see the fuel being sprayed and if you have a leaky injector you will also see drips of fuel along with the spray.....some of these trucks had what is called a " Hot Fuel Handling switch" which has been known to cause this type of problem too

 

Can you explain the "Hot Fuel Handling Switch" a bit better? We have a problem with our 90 model. It has an irradic surging at idle and in drive. Figured I would ask and see if it has some of the symptoms we are experiencing.

 

The hot fuel handling switch basicly tells the computer how much fuel to feed when the fuel system is warm and the motor is at temp...this helps with vapor lock, if the module is "going" bad it can cause some of these symptoms....its more complicated than that and I dont fully understand it....I will look for some info and post it here