My son's 90 firebird, 5.7 starts but idles ruff and dies when applying gas. We just replaced the fuel pump. It starterd fine, parked it and when we started it, it was acting up. It seems electrical. You can hear the pump working and there is pressure.

Welcome to the Formula Source, Len. I don't know much about the '90 5.7 liter, but I'm guessing that somebody here will be able to help. If you could fill out the information in the Tech Tool Tray, it would be very helpful. Am I correct in assuming that it's tune port injected?

What prompted you to replace the fuel pump? Was it having this problem before the replacement? One hard lesson I've learned is that new parts can't always be assumed to be good parts. As you're troubleshooting, don't skip over parts you've replaced thinking that they have to be working because they're brand new.

There was very little pressure at the fuel rail. One of my mechanic friends thinks it my be the TPS. You can slowly open the throttle all the way with no change.

Hello,

I agree with Barcelow, just because a part is new doesn't mean it's good. But for the time being, let's assume the new pump is good. Two main parts to check yet for low fuel pressure. A severly plugged fuel filter could cause fuel pressure, but a faulty fuel pressure regulator is more likely. If the filter has been in there a while you might as well repalce it anyway. If hata doesn't help, try disconnecting the vacuum line from the pressure regulator and look for fuel. If there is, it definitely needs replacement. Also try clamping the return fuel line and retesting the fuel pressure. If this raises the fuel pressure up towards 40-50 psi, the pump is good and the regulator needs replacement. If the pressure is still real low, then the new pump was a failed part from the beginning. I hope this helps in your diagnosis. God bless.

-Chrvlt283