My 89 305 TBI starts OK, then immediately starts to die. I can prolong its death by manually operating the throttle body, but it coughs, spits, etc. Its not pretty. After checking out everything, I put a 30 psi (calibrated) pressure gauge in my supply line just before the steel tube that feeds the TBI. There was no pressure with just the pump running (key ON, engine OFF-pump runs for 2 seconds as it should). The pump pumps a pint in 15 seconds, per the GM specs. During the period that the car starts and tries to run, the gauge doesn't move. It seems that the pressure regulator in the TBI body, or the fuel pump itself, is bad. TBI was rebuilt using Borg-Warner kit 400 miles ago, including regulator. Fuel pump is original (115K miles). New inline filter also. My main question is: Shouldn't the fuel pressure be something around 9 to 14 psi during these conditions? Any guesses as to which one is the likely problem area?

 

Moving to TBI board....

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JSP Motorsports
ICON Motorsports

 

guess would be bad fuel pump. either that or your pressure gauge is wrong. i think if you do a search of the archives for bad fuel pumps you will find simmilar symptoms in their situations.

 

I guess I'll go for a new fuel pump. BTW, do you know how the gas cap is supposed to work? Why does it seem like the tank is under a vacuum whenever I take the cap off? Does it have some kind of pressure relief setting? Does the vacuum come from the fuel being removed from the system by the pump, or from the vapor canister system?

 

its supposed to do that. actually, when you are doing work on the fuel lines or taking the tbi off or something like that. all you have to do to release any pressure in the lines is remove the gas cap.

 

Go stand at the back of your car and have someone turn the key to on. I f you can hear the pump come on and still get no pressure, it's a bad pump. If it doesn't come on check fuses and relays.

Zac Spalding