I am new to PT, so hope I'm posting in the right place. Last week re-installed motor in my 08 GMC Sierra SLT after AFM delete, bigger cam, head work etc. Tuner programmed my computer( out of truck), put motor back in, started first crank, then ran like s$@t. Checked, double checked all the mechanical stuff, couldnt find anything. Talked to tuner who swears the tune should be dead nuts and says its because of low fuel pressure,(42-44 lbs.) Yesterday swap out stock pump for Aeromotive Stealth 340, fire it up and 44 lbs. Fuel pressure is low, fuel trims are 29%-33%, getting codes for lean and an intermittent o2, but nothing else. Have been over this thing with a fine tooth comb, checking grounds, sensors, vacuum leaks, etc. and dont know where to go next, other than crazy. Anyone have similar experience and have any ideas. Tune or Mechanical?? Thanks

 

fuel pressure regulator kicked the bucket. Unhook the vacuum hose from the regulator, see if pressure goes up or fuel comes out.

 

Not on an 08???

I think those have a Module that regulates voltage or something.

I haven't worked on 1 personally so I am unsure. It should be around 58PSI though.

 

Sounds tune related

 

08 has no pressure regulator, it has a fuel pressure module, in the under hood fuse block. Fuel pressure actually dropped from 44.9 to 42.6 after installing the nee pump, which will flow up to 90psi. Also, everything was working fine before the timing chain broke, which started this whole thing.

 

FPCM controls fuel pressure so it doesnt exceed 43 psi until load occurs where it needs the extra fuel pressure


truck runs like crap cause tuner guessed on the calibration, take truck to place to tune it in person

 

I would have to believe the Fuel pressure assembly has an issue and is bleeding off pressure.

It should be around 58 PSI when running. I believe the Spec is 55-62PSI. but I don't have that info in front of me right now. Also, It should not bleed off.