1998 yukon wont start. no fuel problem

[jessica_n_dean]

my yukon out of the blue wouldnt start after work. no problems prior to this. So, i check all the fuses including under the hood. replaced the fuel relay switch. replaced the fuel pump. have even banged a bit on the tank (a few people told me that that might get the pump to work). Still nothing. pump does not turn on when i turn the key. What else am i missing? thanks,
dean

[rosalyn]

hello jessica n dean,

i to own a yukon xl and i have just recently had a problem where the truck won't start, the low fuel light keeps coming on but there is a full tank of gas. I have replaced the fuse but unfortunately that only gave me another week of working before the fuse blew again. I waws initially told that i would have to replace the fuel pump and how costly that would be but after having a test done on the truck i was glad to find that that was not the problem. right now i am convinced that the problem is that the computer (brain) of the truck is not communicating and that the dealer may be able to flash it so that it will reprogram itself or i am going to have to buy a new brain and have it placed in the truck by the dealer. i hope that i have shed some light or maybe a similar problem with our vehicles or if possible please let me know what ideas you have on what could be the problem. Thanks Rosalyn

[jessica_n_dean]

Well, I am taking it to the dealer tomorrow to have some tests done. I'll post on here what the problem is when i find out. Didnt want to have to go that route but I am out of ideas (that i can fix myself) and I need the truck back. Hopefully, it will be minor. thanks,
dean

[jessica_n_dean]

actually, thought today it might be the fuel pump relay control module so I will test light the wires and see if that's working. that's the only thing left that i forgot to replace in the electrical part of the fuel system other than the wires itself. if that isnt it, then it's going to the shop. i'll fill this in as i figure it out i guess.

[Blue Bowtie]

Before going much further, the fuel pressure should be tested. If the pump/FPR cannont make at least 61 PSIG while cranking, there is a problem with the pump or FPR. If the fuel system pressure is at of over 63 PSIG whiel cranking, the pump is not likely a problem.

The fuel pump is very sensitive to voltage. Even a slight drop in pump voltage will lower pressure enough to prevent starting. The relay is a good place to start (since it's easily accessible), but don't stop there. There is a connector under the vehicle, just forward of the fuel tank. Try to back-probe the connector with voltmeter probes and read the pump voltage with the relay energized or jumpered. If voltage is significantly below battery voltage at the pump connector, you have a connection problem somewhere. Unfortunately, that is not the only connector involved. There is another on the top of the tank, another just inside the top of the tank, and yet another connector right at the pump itself. Further, there is a pump ground connection near the connector you just back-probed and tested, and it may have resistance due to exposure to road spray and contamination.

[MT-2500]

Originally Posted by jessica_n_dean

my yukon out of the blue wouldnt start after work. no problems prior to this. So, i check all the fuses including under the hood. replaced the fuel relay switch. replaced the fuel pump. have even banged a bit on the tank (a few people told me that that might get the pump to work). Still nothing. pump does not turn on when i turn the key. What else am i missing? thanks,
dean

As said check that fuel pressure.
Some guide lines on checking fuel pressure.
Hard to start cold or just hard to start..
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
Post back fuel pressure readings.