I have a 91 Pontiac Firebird Formula V8. Recently I changed the fuel pump, stocking, and throttle body. Yesterday, she ran like a dream. Today - nope. I notice I'm getting fuel in my fuel filter even when the ignition is off. Any ideas? Do I need to replace the pump...again?


I'm not sure I'm following your question. How are you checking your fuel filter? The fuel system will retain fuel pressure (~43psi) even with the key cut off, so you will get fuel out of any part of the fuel system - from fuel pump to fuel rail - if you break something open. Very normal.

EDIT - NOTE: The 43psi quoted above refers to the Tuned Port Injection (TPI) setup. If Throttle Body Injection (TBI), the fuel pressure will most likely be lower as stated in the comments.

  • GM TBI uses low pressure, like between 12 and 15psi. – Jimmy Fix-it Sep 3 '16 at 18:20
  • @JimmyFix-it - If the engine in this vehicle is fuel injected (OP doesn't state), it will have the Tuned Port Injection, which will have ~43psi. To my knowledge, these cars didn't come with TBI. The OP does state he changed the throttle body, which would indicate a TPI setup. – Pᴀᴜʟsᴛᴇʀ2 Sep 3 '16 at 18:24
  • OK, but I owned a 91' 5.0 v8 (305c.i.) Bird with stock TBI, not TPI. – Jimmy Fix-it Sep 3 '16 at 18:39
  • @JimmyFix-it - While I've never seen this, I did some checking and you are correct. I would bet finding them like this would be slim pickins ... I stand corrected. – Pᴀᴜʟsᴛᴇʀ2 Sep 3 '16 at 18:44
  • No worries, they probably had different stuff on different models maybe. I tend to think of the cars I bled on to be the only ones that matter, lol : ) – Jimmy Fix-it Sep 3 '16 at 18:53

Before you replace the pump (again) you should troubleshoot. I would start with a check the fuel pressure. This should tell you if you have a pump issue, a pressure regulator issue, or a blockage or some other problem.

GM TBI does not have a regular Shraeder port on the fuel rail for testing fuel pressure. You will need to get ahold of (borrow, buy, etc.) an aftermarket piece that you place in-line in place of your fuel filter, it has a test port for a traditional FI fuel pressure test gauge. Pressure should be between 12 - 15 psi. Too low = fuel pump issue (or obstruction of some sort), too high = pressure regulator issue (or perhaps obstruction of fuel return line).

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