txbanditswraith

i bought a new walbro 255 fuel pump and when i have the rpms steady at any level the psi drops to 35 36 again what can be causing this the car came with a holley fuel regulator also dont know what else to look at

Kmaroman

iTrader: (1)

what year is your car 93 f-bodys only make like 42-47psi not sure on 94s but on up they make 55-57 i believe. Unplug the vacuum hose of the regulater and see what your psi. After you unplug the hose, redo your fuel pressure test first with the car on but not running to see if it holds PSI. See what your readings are then do it with the vehicle running. With the vacuum hose pulled of the regulater it'll show you just how much fuel pressure your pump is putting out

LT1

iTrader: (1)

LS1's have around 50psi

LT1's are around 43psi

txbanditswraith

its a 96 trans am lt1

kinglt-1

iTrader: (26)

Should be 43psi. I would get a stock replacement regulator! Ive seen more problems with the aftermarket ones and almost none with the stock. I will say the aeromotive stuff is pretty good tho! Also what walbro kit did you buy?

txbanditswraith

i got the kit off new era prformance http://www.neweraperformanceparts.co...KV=walcamaro|0 thats the one i got it has the niple in the middle not on the side.

txbanditswraith

i was playing with the throttle and i was holding it steady at 2400 to 3000 and the psi would drop to 35 36 psi

Kmaroman

iTrader: (1)

unplug the vacuum hose running to your regulator then tell me what you get

txbanditswraith

alright i unplugged vacuum line and the psi is at 42 43

kinglt-1

iTrader: (26)

It's the regulator! Buy a new ac delco and you should be good.

txbanditswraith

where is it suppose to be at when unpluged cause it has that screw to mess with it

kinglt-1

iTrader: (26)

LT1 Fuel pressure= 43 psi. plug the vacum line back in and adjust the screw. If it won't adjust replace it.

Kmaroman

iTrader: (1)

its the regulater sorry for the news, take it back and get a refund

RoAdRaGe912

I havn't seen proof it's the regulator yet. Fuel pressure ~43 psi with the vacuum line removed is not indicative of what the pump puts out, it is what the fuel return style regulator is regulating the pressure at with zero vacuum reference to it. If that's the pressure it's holding at zero vacuum, then that is correct.

You also need to know what the fuel pressure is at idle and WOT (not just the vacuum line removed, although it should be the same). Fuel pressure is not supposed to be stable at 43 psi throughout the rpm band, that's why the vacuum reference line is there.

Fuel pressure should drop 3-10 psi at idle, and therefore at less and less vacuum (more and more throttle) the pressure will increase towards ~43 psi.

Are there performance issues with the car? I have seen plenty of aftermarket regulators fail, but it could be nothing (haven't seen a problem until you post psi at idle with the fuel line connected), or a vacuum issue.

94LT1420

Did you change your fuel filter?? It could be clogged....

kinglt-1

iTrader: (26)

43psi is what the pressure should be at idle.

txbanditswraith

i started adjusting the fuel and with vacuum off its at 49 psi and with vacuum on regulator its at 43 psi is that right?

RoAdRaGe912

Wrong. It should be at 43 psi with ZERO vacuum reference, which means the vacuum line disconnected when it's running, or with Key On Engine Off where the fuel pump is on for a few seconds, but the engine is not. At idle the throttle blades are the most closed they can be, therefore you intake manifold is at the lowest pressure (highest vacuum) it can be. The fuel pressure regulator is a pressure regulator with a reference line to the intake manifold. This makes it a basic differential pressure regulator between the intake manifold and fuel rail. The lower the pressure of the manifold, the lower the fuel pressure in the fuel rail.



No, with the vacuum line disconnected it should be close to 43 psi. With the line connected and the car idling it should drop 3-10 psi. At idle manifold pressure will be the lowest, so that should be the lowest fuel pressure you see. It should increase towards 43 psi as you give it more throttle.

http://shbox.com/1/4th_gen_tech2.htm...essure_testing