Hey guys and gals, 1988 Fiero GT 5 speed here. 43,500 original miles. Runs great in general, idles at 1600 cold and 950 warmed up. Sometimes though it just won't start and needs cranking for 20 seconds to fire cold or hot. All the usual tune up parts are all new. I installed a fuel pressure gauge and it primes to 28 psi and holds, no bleed down. It won't start. Sometimes though it shows 42 psi and holds and starts right up. Is this strictly the fuel pump dying or can it be some other issue? All of your opinions and suggestions will be greatly welcomed. Thank you

quote I installed a fuel pressure gauge and it primes to 28 psi and holds, no bleed down. It won't start. Sometimes though it shows 42 psi and holds and starts right up. Is this strictly the fuel pump dying or can it be some other issue?

It may indicate a problem with the fuel pump or the fuel regulator which the latter is easier to fix.....

I believe fuel pumps won't hold pressure to 34-46psi; not intermittent {but maybe I'm wrong....}

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Original Owner of a Silver '88 GT
Under 'Production Refurbishment' @ 136k Miles

[This message has been edited by Vintage-Nut (edited 11-13-2025).]

Thank you V-N, the fuel pump sounds the same as it always did when priming and it is the original. I would think the pressure would start dropping if the regulator was leaking though?

The fuel pressure regulator is responsible to maintain pressure in the fuel rail by controlling flow in the return line.

It also serves as a load compensator by increasing fuel pressure at times of low manifold vacuum.

To me, check the fuel pressure regulator before dropping the tank....

quote Originally posted by firejo24: With low fuel pressure there is one more thing that could cause the problem. Before condemning the pump, you should really run the proper GM fuel pressure test. Pinch the fuel return line and then activate the pump. If the pressure is normal then the fuel pressure regulator is bad. If it’s still low, then it’s the pump (or feed line on the pump output).

[This message has been edited by Vintage-Nut (edited 11-13-2025).]

Thank you again V-N I will try that first and I have a new one on hand thankfully.

I would also check/replace the fuel pump relay. There is easy access to it on the left side of the firewall. The ECM energizes it when starting but when it doesn't function the oil pressure switch takes over and may cause a delay in starting. Worth replacing as its an inexpensive part and if the relay is original it's a good idea to replace it..

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

quote I would also check/replace the fuel pump relay.

Good point...

Hi Dennis, the fuel pump relay has been replaced about 3 months ago as well a new Oil Pressure sending unit last week. The relay clicks and the pump primes just like it always did. On the gauge sometimes it only gets to 28 psi and then won't start but the odd time it shows 40 psi then it starts like new.

Other thoughts on a fuel pressure drop issue:
*Leaky fuel injector(s)
*Clogged fuel filter

[This message has been edited by Vintage-Nut (edited 11-13-2025).]

Hello V-N, the fuel filter is brand new about 2 weeks ago and the pressure holds, it doesn't drop like in some videos I saw. Sometimes it only builds to 28 psi but other times it builds to 42 psi and then it starts just fine.

As with any puzzle, the more information you have, the easier it is to solve.

My advice is that it is crucial to diagnose the issue thoroughly before replacing the pump

Be a troubleshooter, not a trouble-guesser...

Carefully investigate the failure and invest time to discover the root cause:

*Voltage / Electrical Connection Problem? {The relay may 'click', but is the voltage going to the pump?}

*Fuel Pressure Regulator Problem? {Did you pinch the fuel return line, and ran the fuel pressure test as suggested?}

With voltage at the fuel pump AND the fuel return line closed; a Fuel Pressure problem can be the pump OR leaking injector.

*Leaking / Sticking Fuel Injector? {Ideally, take them out and sent them to be cleaned and flow tested}

To me, dropping the tank to replace the Fuel Pump is the LAST thing I would do....

Good Luck

[This message has been edited by Vintage-Nut (edited 11-14-2025).]

For fuel pressure testing purposes... I would suggest taking the relay out of the equation, by connecting 12v (from the cigarette lighter) to the fuel pump terminal of the ALDL port.

I had similar problems as you are experiencing a few years ago. It ultimately turned out to be the fuel pump. The filter on the fuel pump had come apart. Bits of it were not in the tank so I can only assume it got sucked into the pump and damaged it. A new fuel pump fixed the problem. No more cranking for several seconds before starting or not starting at all.

Dropping the tank is not fun but it is not the hardest thing to do either. If you decide you need to do it, I would have extra fuel line and vacuum hoses on hand so you can replace the lines while you have it out. I would replace the fuel pump even if it looks good. The fuel pump is not that expensive and I would not want to have to drop the fuel tank twice if I made a diagnostic mistake. $40 is worth it for me to not have to do that job again.

Good luck.

Thank you for the feedback Doug85GT, it is unfortunately looking like i have to go this route. Other posts I have read on this exact issue after trying everything else it ended up just being the pump itself. It will be 38 years old soon and I do have a new sending unit assembly and Rodney's pumps so next spring it looks like i will have to do this! Thank you to everyone for their input. I appreciate it