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?
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2 Answers
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.
answered Sep 3, 2016 at 17:52
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@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, 2016 at 18:24
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OK, but I owned a 91' 5.0 v8 (305c.i.) Bird with stock TBI, not TPI. Sep 3, 2016 at 18:39
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@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, 2016 at 18:44
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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 : ) Sep 3, 2016 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).
