Irocz_newbie

Well the story is I have a 89 Iroc Z with the 5.0 Tpi motor. I recently redid the whole fuel system, Injectors, pump, and I was told the regulator was new. My problem is when The pump primes when I turn the key to on, the fuel pressure will jump to like 45, then drop to zero immediately. Where do you guys think my problem is??? I did the injectors (ford 19lb) and they arent leaking and the pump (holley 255lph) the only one I didnt do was the regulator, But I was told it was new when I bought the car.
So again, where do you guys think my problem is???

Thanks

Street Lethal

iTrader: (16)

It supposed to do that with the key in the ON position. Turn the engine over, you should see a constant 45psi reading...

Irocz_newbie

I know its normal but arent these cars supposed to be able to hold the pressure??? Thats what mine isnt doing, it isnt holding the pressure. When it starts its steady,but then when i turn it off the pressure drops back to zero immediately.

Street Lethal

iTrader: (16)

Power to the pump is killed, and with the fuel return line being prevalent, why would pressure in the system still be remaining?

DJP87Z28

When you turn on the key without starting the engine the Fuel Pressure should be 38/40 PSI and hold steady. When you start the engine it should remain about 40PSI with NO drop off in both positions. Even when you turn the key & engine off the pressure should be a slow return to ZERO over about 1/2 hr or about. NO instant drop to ZERO pressure. You have a leak in your system.

Street Lethal

iTrader: (16)

If what you say is correct in reference to holding pressure for at least 1/2 hour, yet his gauge is immediately going back down to 0-psi, from 43-psi, then he must have one heck of a leak on his hands....

Curious, what kind of pressure gauge are you using, and is you're fuel cap on?

DJP87Z28

I have a under the hood FP gage, that why I know it takes a while to return to ZERO.

Street Lethal

iTrader: (16)

My apologies, but that question regarding the pressure gauge, and gas cap, was meant for the original poster, Irocz_nembie...

Irocz_newbie

Well Im using a pressure gauge that mounts to the fuel rail. one from kragen.
as for the fuel cap question, yes my cap is on but my filler neck is leaking. I didnt know these tanks worked that way since they dont have baffles. So would the leaking filler neck be the cause of the drop off in pressure???

thanks

Street Lethal

iTrader: (16)

I would imagine with the pressure drop being as drastic as you're indicating, it's more than likely the source of you're problem...

Elephantismo

I went out and checked mine. It holds 48 psi with the cap on or off. I've got a 91 z28. Could be a different system. You have an intank electronic fuel pump? The pump itself is suposed to have a one way valve that holds pressure in the line if i remeber correctly. It could be that that after market setup you have doesnt include one. you could add a one way valve at the inlet tubing union up at the motor.