1995 Gmc K1500 Runs Rich, Please Help...

[BBC]

Hoping someone can help me. I have a 1995 GMC K1500 Ext cab pickup. It is actually called a "Z71". I never seem to find this when trying to reference for parts. The truck was sold to me second hand with 190K miles. It has been maintained immaculately by my friends father who sold it to me (service records, etc). I recently changed to plugs cuase they were about 90K on them and the engine was clearly fouling on some cylinders. Two of the plugs were completely caked with some sort of sludge. This solved that problem. However, The truck runs extremely rich. My friends told me that i about gassed them out with exhuast fumes when following me in their car. The exhaust is extremely rich with fuel smell, specifically unburned gasoline. I have done the basic stuff (air filter, plugs, checked for obvious problems like loose vacuum lines. I don't know where to go from here. I I know this vehicle is fairly computerized. The problem does seem to vary from time to time. I think this engine has some kind of throttle body injection. Could it be a choke issue?? but the gas seems heavier than that. Could failed O2 sensors cause this problem?? Sorry if i have not provided enough information. I would be happy to give more. Any help would be GREATLY appreciated. Thanks in advance.

[neev_nav]

Failed o2 sensor could definately be the problem. Couple other things to check are coolant temperature sensor and the fuel pressure regulator. I have a 94 that ws running rich and it was because my fuel pressure regulator was totally rusted out and letting too much fuel in. But definately check those things out. If the coolant temp sensor is shot then it could be telling the computer that the motor is a lot colder out then it is and it is flooding gas in. Just some food for thought.

[Kevin45]

Does the Ckeck Engine Light ever come on? If so, then have the codes checked that it stores in the computer. If it does not come on, is it operable when you turn the key on? O2 sensors could cause it, EGR valve could be the culprit, and like neev-nav stated, the coolant temp sensor could also cause the computer to act differently. After you changed your plugs, did you do anything like check the timing? And does the truck miss any while idling? A few more answers are needed.

Kevin

[neev_nav]

Yeah if it's the coolant temp sensor or the o2, it should have sent a code. FPR on the other hand, you'll have to take apart to check.

[BBC]

There has been no chk eng lit since the plugs were changed. That stopped all "rough" running. The engine does run sluggish. With all the reading i have been doing, it has raised my concerns about the caty convtr. The has been a strange rattling comming from underneath that sounds like sheet metal. Could there be damage to the converter from the heavy fuel mix. Or maybe it just failed from age? Could this be causing my problem. Does the caty convtr feed back into the computer? Sorry for the abbrevs. I guess you find out your spelling skill when posting.

[neev_nav]

I don't think a damaged Cat would cause it to run rich, but it could be damaged because it was running rich. How many miles are on the truck? Cause if it's a 95 it could definately be the fuel pressure regulator.

[bwood]

Remove the air cleaner and start the engine. Watch how the fuel injectors spray. It should be very fine, almost hard to see. I had a similar problem on my first truck, 91 GMC Sonoma w/2.5, it only had one fuel injector. It fouled plugs in about 1k miles and it really sucked down the gas. The fuel injector was spraying on one side and just had gas running out on the other. Bought a reman injector and some new plugs, problem solved.

[texanidiot25]

How easily does it start? Does it seem to smell gas-y right after starting, and it takes a while to crank (sometimes needing to pump the gas)?

Sounds like the fuel pressure regulator. Same thing is happening to our GMC Jimmy.

[BBC]

Thanks for the replys. I'll start with the O2 sensors and visually the flow from the injection system. I'm going to have to figure out where those other items are located.