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Virtual Wrench
Virtual Wrench, Pontiac Mechanic
Category: Pontiac
Satisfied Customers: 14612
Experience:  35 years Master Mechanic
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93 pontiac firebird formula: fuel runs..12 volts..the pedal

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hey, ok so i have a 93 pontiac firebird formula, just replaced the optispark, and fuel pump. car runs solid! (although voltmeter sometimes runs higher than 12 volts ) solid starts, than some low rpm and seems when i step on the pedal she won't take the fuel sometimes. now she won't start at all! won't turnover and i don't hear the fuel pump? bad fuel pump relay or ground? any ideas?

Hello and welcome!


If the fuel pump was an aftermarket pump it could very well be the fault. Given the history on these fuel pumps, it is not uncommon at all for a new one right out of the box to be defective, or even if it does work, a lot of times they don't work for long.


Couple of things you can test to determine if it is at fault. First check for power at the gray wire going into the fuel pump while someone is trying to start it. You can't just turn the key on and then check it because power drops off after 2 seconds if the engine is not turning. So you would need a helper for that. Next, if it does have power at that wire, install a fuel pressure gauge on the fuel rail test port (looks like a tire valve) and measure pressure when trying to start it, it HAS to have about 45 psi, and if it is much lower it wont be enough to open the injectors. If low, replace the pump with one from the dealer. If there is no power at the wire to the fuel pump, probably the relay.



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Customer: replied 5 years ago.
thanx, this is the fourth fuel pump in 5 years, would could cause a fuel pump to burn out? and do fuel pump relays show signs of going bad? i heard they work or don't. could it be a fuel pressure regulator?



Yes, if it is an aftermarket pump i am not surprised that you have replaced it so many times. They are just sub standard and there is so much competition on the aftermarket that a lot of parts stores just buy the cheapest ones. Sure, they may warranty one if it fails soon enough, but they sure won't come out and put it in!!


Yes, the relays are kind of funny like that because the contacts can intermittently not make good contact sometimes, and sometimes they just fail completely. For the most part though, they usually do just quit working with no signs of anything...


As far as the regulator, if you remove the vacuum line to it and there is any signs of fuel in the vac hose, then replace it. Also below is the testing procedure.






Nice ride you have there, best wishes!


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Customer: replied 5 years ago.
thanx will do, one more question, where is the fuel pump relay located in a 93 firebird formula?



They have it tucked forward of the driver side kick panel, on foot rest bracket, under the carpet. Below is a diagram that kind of shows the general area, but you will have to dig around under the carpet and you will find it. You can use the wiring colors to confirm you have found it.




Thanks again!


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Customer: replied 5 years ago.
thanx you have been very helpful! wish me luck

My Pleasure.


Thank YOU for asking.


Best wishes my friend!