Long time lurker, first time poster. I am trying to help a neighbor with his denali.
It quit running on Friday night. He got it home and on Saturday morning it started right up, but would die. The engine is a 6.0.
Yesterday we checked for spark; got a real weak orange spark from 6 plugs. It finally started and I could smell raw gas at the tail pipe. It idled rough at about 600 RPM. I tried to give it gas and it would die. We changed the spark plugs(166,000 miles), and still have the same symptoms. It's as if the injectors are flooding the cylinders with gas.
I checked the ECM1 and ECMB fuses and the injector fuses. They were intact.
My neighbor plugged his code reader in but it stayed blank, like there was no communication link. We checked the reader in another car, and it worked fine. Someone told him if the reader did not work when plugged in, then his computer is bad in them vehicle.
I don't know what to do next. Any advice or recommendation would be greatly appreciated. Thank you

Jimmy

 

The cig lighter fuse is blown that is why the code reader does not work. The power wire for the data link connector shares the light fuse. The computer is not bad. You need to check the full pressure I am sure you will find it to be low.

 

MDTahoe, thanks for the reply. The fuse was blown. We're going to try the code reader now. thank you

Jimmy

 

Should I check the fuel flow at the fuel rail by disconnecting the fuel line or should I use a gauge? I'm confused as to why I smell so much raw gas at the exhaust outlet if the fuel pump is bad.

Jimmy

 

The truck will run about 10 seconds, idle gets rough, and it dies. We plugged in the code reader and it showed "0 Codes". Maybe the truck isn't running long enough to produce a code. I'm beginning to think it may be a bad fuel pump, but I don't have a gauge to check the fuel pressure. Does anyone know what the fuel pressure should be? I appreciate any help

Jimmy

 

I found the schrader valve. I released the pressure, there was only a few drops of fuel. Turned the ignition key on to run the fuel pump. I depressed the valve again, and there was no pressure at all. Am I correct in assuming my neighbor needs a fuel pump? Thank you for your help

Jimmy

 

Most likely need a pump. You smell fuel because there is fuel just not enough to burn.

 

Thank you MDTahoe, I appreciate your help. Would you recommend ACDelco over an aftermarket unit? Thanks again

Jimmy

 

AcDelco or Delphi only everything else will fail prematurely

 

The fuel pump was replaced under warranty. The shop drove the vehicle to check it out and it quit. The mechanic said it was not the pump. Asked why he replaced it. Replied, no fuel pressure. Now he says it could be an ignition module or coil or something else. Asked him to check it on a diagnostic machine. His reply was that it wouldn't do any good. This is my neighbor's mechanic, not mine.
Is there anything else that I can help him check, providing I can rent a gauge or meter? Thank you

Jimmy