Air / Fuel mixture too rich?

Your air/fuel mixture is determined by the computer and is not adjustable. The computer (PCM) relies on signals from O2 sensors, MAF, IAT, etc. to determine how much fuel to dump into the motor. A failure of one of these sensors or a fuel delivery component itself (such as pressure regulator, injectors) can also cause a rich running condition.

Seeing as how your motor has 3-4 02 sensors, I'd be willing to be they changed the wrong one.

Doc

If you smell gas from behind the wheel while driving, it sounds like an underhood gas leak. It might only leak when the plumbing gets hot, but it should be easy to find. It would also smell after shutting off the engine since the fuel plumbing is pressurized and would continue to leak until the pressure bleeds off.. Be careful you don't have an underhood fire.

Randy

That and he might check the engien temp sensor for the ECM because it may be telling the ECM that the engine is still cold when it is hot and this may not cause a fault code either.

Thanks for your advice.

Do you think the codes would come back clear if they changed the wrong O2 sensor? Also, I've been told about 3rd party "custom" programs for modifying or tweaking the settings in the computer. Does this exist for all GMC trucks, or is it a myth?

BS

Would that be the same as the one for the engine temp on the instrument cluster? That one seems to read properly. Starts out cold and gradually rises to normal running temp.

I'll check back with the shop about this. Thanks.

BS

Thanks for your advice.

No, the only place the gas smell comes from is the exhaust pipe. There are no active leaks on the ground when the vehicle is parked. If I keep the windows closed I don't smell it at all. But if I open the passenger side window the fumes get unbearable within a minute. Also, when I accelerate suddenly, there is a lot of grey smoke coming from the exhaust. There is a build up of soot on the body just above the pipe.

I'm told the vehicle is "over fueling" - which to me means too rich a mixture.

BS

No, different device. The one that feeds the temp guage is called the coolant temp SENDER and is located on the left head, between cylinders 1 and

1. The one that feeds the PCM is called the coolant temp SENSOR is is located somewhere close to the waterneck/t-stat. They do not interact in any way, shape or form.

Doc

Not a myth, but it should run fine without buggering with the computer's fuel maps. There is something wrong, and adjusting the computer to compensate will just band-aid the problem if it does anything at all.

Doc

Here's a thought. . .

Back in early March the truck was in a different shop to get the head gasket replaced / redone. When they put everything back they somehow mis-aligned the dipstick tube and for the next few weeks it worked its way close enough to the positive post on the alternator that one day it shorted out and fried the battery and much of the wiring.

Could this have affected the computer somehow? It wasn't too long after this happened that the fuel smell became apparent. Sounds wierd, I know. But I thought it was worth mentioning.

BS

given that information, I'd say you smoked the computer and it's running off the CALPAK, which runs things waay rich to protect the motor.

-Bret

Yeah, that little tidbit of information would have been useful further up in this thread! Good ol' limp-home mode................

Doc