Where are you located? I am in Chattanooga, Tn. Sound like may be a simple O2 problem. When at WOT the pcm ignores the 02. Would have to look at the adaptives on your car to determine what direction your mix is. With the backfiring sound like the pcm is leaning out. Can EASILY be determined on the adaptive screen. Doubt if fuel pump due to running good at WOT.

 

chattanooga......sounds familiar
i live about 1 hours south of rockford, IL

i dont have a downstream 02 sensor.....but i didnt think that would make a difference....
i dont know anything about how to tuen the car....so i might have a look at it a little today if i get a chance[&:]
if anyone can help, and needs a list of everything that is done, just let me know

 

i get a prob simular to this once in a while when my turbo melts the vac lines and T splits to the fmu. however getting to rich during spool will also do it.

 

i figured its gotta be too rich or too lean.....but i dont know what the fuel pressure should be at in the first place....so its kinda hard to set it right

i know the vac lines are still good......and i usedbrass t-fittings

 

Downstream only monitors the converter. The upstream is the feedback for the adaptives. List what you have anyway.

 

ok, the list is kinda long, im gonna list everything incase there is some relevence to the situation
srt-4 turbo running 6psi
srt4 intercooler
hard pipes
srt4 cat convertor
2.5 inch exhaust pipe
vibrant dual exhaust muffler
mopar srt4 BOV
AOBE map clamp
AGP ajustable wategate
aeromotive 13105 fuel pressure regulator
walbro 255lph external fuel pump
walbro 255lph in-tank fuel pump
1/4inch fuel return line
stock fuel injectors
stage 1 clutch
there is a few other things that im sure im not thinking of at this time as well as some non turbo related parts

 

youll have to adjust the fuel by trial and error its the only way at this point. unless you have a dyno around that could save you a couple hours.

 

i guess i will just tinker with it for a bit.....i dont even knowwhat its set at know.....if i go outside soon i will check the pressure......but i dont know how high is too high....or how low is too low

 

IF you had a DRB you could also watch the adaptives and adjustto get adaptives close to 0 or at least single digits. The pcm will automaticly adjust for low pressure or high pressure by increasing or decreasing pulsewidth. (why they are called adaptives they ADAPT) Stock pressure should be 58 +/-5 psi. If it backfires that is a lean misfire, so pressure may not be high enough or a bad02 due to runs ok at WOT.Could also be a incorrect reading from map (incorrect baro reading), or ect reading too high (hotter engine requires less fuel). If you were CLOSER would not be a problem. LOL

 

Are you getting any codes? May want to consider having a look at you VSS, as it is kknown to do such things before failing completely.