I have had my 04 GMC Sierra for about a year now. Right after I got it, I expierenced a little "road rage" when this a-hole was tailgating me, and then decided to pass me in a 40mph zone on a double yellow. He got to my door and I "floored" it and the truck downshifted and then fell on its face. Truck is all stock except the 5" down pipe back. It happend to me again the other day getting on the highway. It has only happend to me twice so far. But, I have a few more questions. I have had happen to me 5-6 times and for no rhyme or reason after I let the truck idle for a few mins after driving long or short distances, and get back in to go, the truck will "load up" kinda like a float sticking on a carbureated motor. It will spit and spudder and carry on with some greyish smoke, then all of the sudden it will belch a big cloud of black smoke and take off like a rocket. My fuel mileage has dropped about 4 mpg since I bought it. It started at 18 and now the best I can get is 14. It currently has 116000 miles on the odometer. 3650 hours. I bought the truck with 98000 miles on it. So I have put about 18000 miles on it in the last year. I have had the oil changed 3 times and changed the fuel filter 6 times. There has been no check engine light at all. There is also this "squirting/hissing" noise under my truck as well. Does it at idle in park or any gear, goes away about 1500 rpm. Any feedback will be greatly appreciated.

there is an ECM reflash that might help you....but I suspect that you might have the injector harness rub issue so common on LLY trucks.

http://www.dieselplace.com/forum/showthread.php?t=142114

I forgot to add the harness is on the opposite side of the bracket thats referred to in the "rub condition"

There is another part of that problem, the harness begins to pull away from the injector itself as described in that write up...Rick goes into great detail on how to fix that problem.

While the rub issue is common, the harness loosening is unrelated to the harness rubbing on the alternator bracket.

very interesting link. I was relating both the 2/7 problem with the rub problem, so I will start next with that.

Many threads on that and it was a fairly common problem with 04.5 -05 LLY's.

I had an 04.5 and luckily never had that problem.

I'm also wondering where abouts you're located at.

good luck :thumb:

Mount Upton NY. Im 10-15 miles north of Sidney on Rte 8

http://www.dieselplace.com/forum/showthread.php?t=196455&highlight=harness+rub+hose

http://dieselplace.com/forum/showthread.php?t=62181&page=2&highlight=FICM+bracket

And the most informative one with pics.

http://dieselplace.com/forum/showthread.php?t=142114

how bout the noises under the truck? squirting/hissing noise at idle in gear or park goes away about 1500 rpm

my dealer fixed the rub prob..put a peice of rubber on the spot..about the noise...they say "normal"...get your dealer in gear with a little research on this site-:D;)

how bout the noises under the truck? squirting/hissing noise at idle in gear or park goes away about 1500 rpm

Kinda sounds like your variable-vane-turbo doing a position test...

Does the sound change from a good "HISS" to a very deep, throaty rumble at idle?

no its always there, this is different than the variable vein in the turbo.

air getting in fuel line?

nope no air in fuel line

i have heard that the fuel rail is crooked and what is happening is the truck is defueling. or so i heard. have a LLY and i havent run into this yet