between 2k-3k rpm, watching my SAFC (still untuned...) if i let my throttle go to 0% and i punch it it hesitates and stumbles (almost like its running lean). If I let it go down to 1% throttle, it doesnt stumble.

Sounds like the WOT sensor or TPS right? Its not. I changed it. I also put in new plugs (NGK coppers STOCK heat range), cleaned throttle body, new PCV valve and fuel filter. No change.

I did notice one thing. If i watch my fuel pressure, when i mash it, it imediately goes up say... 8 psi, stumbles, then jumps another 7 or so and stops doing it. Could it be my stock FPR?

Any thoufghts would be terrific.

-newman

 

Your fuel pressure goes to 8 psi when you floor it? That ain't right. Your fuel pressure should never go below 34 psi, and when you floor it, it should immediately rise to 43 psi (unless you have a Walbro fp and oem fpr, in which case the numbers will be a little higher). Then when boost starts to develop the fmu will increase fuel pressure from there based on boost pressure and the size disk you're using.

 

i meant that the fuel pressure jumped UP 8psi. It never dips below 38 (idle).

Basically im cruising along on in 4th or 5th, about 2300 rpm. I let off the gas. The fuel pressure goes to 38, throttle goes to zero. I punch it to 50% throttle. Fuel pressure imediately rises to 45. The car stubles while it accelerates for about 1-2 seconds. The fuel pressure then jumps up another amount to say 50 psi and then the sumbling stops. Pressure gauge will not see boost in this time. Is the stock FPR taking too long to "regulate" thus causing the second jump in pressure?

sorry if i was unclear the first time.

 

Oh, okay, that's a relief.

Yeah, it sounds like a fpr problem. The jump in fuel pressure from 38 to 50 psi (that's the number's mine makes, too) should be near instantaneous. Other potential possibilities may be the fuel pump or the fuel filter, but I would bet on the fpr being the culprit.