Fuel Pressure never changes...

[RoadconeTuning]

well... this has bothered me for a long time... my fuel pressure stays at 40psi according to my predator... idle, wot, decel... doesnt matter... the only time i see it change is during tip in... it'll dip to 38 or 39psi and then come back to 40psi instantly...

car has 66k miles on it, stock fuel system, just bolt-ons and the car SEEMS to run fine most of the time... when it is 80+ outside it feels like the car leans out over 3500rpm so i usually get out of it and start trying to pay attention to it...

another thing is sometimes when i start it ti'll go WAY lean about 5 seconds after i cranks... it stumbles and if im moving the car around when it happens and i roll into the gas it just falls on its face an then recovers about a second later...


is this FPDM related or fuel pump related or could it be a faulty pressure sensor on the fuel rail???

remember its just a bolt-on GT with nothing crazy like nitrous or a blower...

 

[oxfordgt]

Do you have your vacum connected to your FPS on the driverside fuel rail? At idle fuel pressure should be 30psi and go to 40psi under load. Tip in should jump up to around 43psi and settle back to 40psi. It sounds like you have no vacum refrence. You really need to fix that.

 

[blkhorse]

I don't know what pressure the predator is reading,but sounds like it is the delta pressure which the computer tries to keep it at 39 psi, so thats normal. datalog fuel pressure,maf counts,02's,iat's,temps etc when the problem occurs could help in finding problem

 

[BobHyatt]

well... this has bothered me for a long time... my fuel pressure stays at 40psi according to my predator... idle, wot, decel... doesnt matter... the only time i see it change is during tip in... it'll dip to 38 or 39psi and then come back to 40psi instantly...

car has 66k miles on it, stock fuel system, just bolt-ons and the car SEEMS to run fine most of the time... when it is 80+ outside it feels like the car leans out over 3500rpm so i usually get out of it and start trying to pay attention to it...

another thing is sometimes when i start it ti'll go WAY lean about 5 seconds after i cranks... it stumbles and if im moving the car around when it happens and i roll into the gas it just falls on its face an then recovers about a second later...


is this FPDM related or fuel pump related or could it be a faulty pressure sensor on the fuel rail???

remember its just a bolt-on GT with nothing crazy like nitrous or a blower...

Forget that reading and hook a gauge to the valve / connector on the fuel rail and measure the pressure _there_. If you unhook the vacuum to the regulator the pressure ought to increase. The exact values depend on your vehicle specifics, but this is the way to check fuel pressure, not thru the computer...

 

[oxfordgt]

He has an 04. Not as simple to just hook a gauge up you have to buy an adapter that goes under the FPS. 99-04 don't have a regulator you can get to in the engine bay.

OP how do you know it is lean after start up causing stumble. It is more then likely a rich condition which is causing it to stumble and fall on its face again pointing to no vacum refrence for the FPS.

 

[RoadconeTuning]

AEM Wideband indicates that it goes over 18:1 and shows "--"

and you are correct in me not having a valve to check fuel pressure with otherwise i would have since i have an 04...


the pressure delta sounds right and is originally what i thought... and i DO have the vacuum line connected to the sensor that sits on the drivers side fuel rail... that is the first thing i checked actually...

ill dig thru the predator datalogs with my laptop and see if i can find actual fuel pressure and not injector deltas....

if you think of anything else please post up.. ive been trying to figure this out for months lol....