Intermittent Fuel Pressure (Page 1/2)
88Fingers NOV 13, 07:17 AM
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
Vintage-Nut NOV 13, 07:46 AM

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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).]

88Fingers NOV 13, 08:09 AM
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?
Vintage-Nut NOV 13, 08:29 AM
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....


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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).]

88Fingers NOV 13, 08:49 AM
Thank you again V-N I will try that first and I have a new one on hand thankfully.
Dennis LaGrua NOV 13, 09:31 AM
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 "

Vintage-Nut NOV 13, 09:59 AM

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I would also check/replace the fuel pump relay.


Good point...
88Fingers NOV 13, 10:06 AM
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.
Vintage-Nut NOV 13, 01:35 PM
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).]

88Fingers NOV 14, 07:58 AM
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.