Injectors not firing after prime (Page 1/4)
Boozeman JAN 03, 11:14 AM
Good morning! My son and his friend have been working on his friend's 1986 SE 2.8 recently, trying to get it running. It had been running fine, and suddenly quit working. They are both pretty mechanically talented, so there's no ham fisting going on. I have not been present for much of the work that they've done, but they have been through most of the ignition, replaced cap, rotor, tested out the ICM and coil, tested the ECM, verified the CAT isn't clogged, flow tested the injectors, etc. So last night I was working with them, and this is where we appear to be... Turn key on, the pump primes the motor. Start the motor, it runs until the prime shot is burned, then quits. It acts as if the injectors are not firing/squirting when the engine starts. They were still tracing the wiring looking for a short when I had to leave last night. What would cause the injectors not to fire?

Any and all help much appreciated!
Vintage-Nut JAN 03, 11:23 AM
Did you check the fuses?
TBI 1 & 2

Edit: Page 8A - 21 - 3 in the service manual
Or page 901 on the digital manual
https://fieroinfo.com/manua...o_Service_Manual.pdf

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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 01-03-2025).]

Boozeman JAN 03, 11:39 AM
Yes, fuses have all been checked and appear to be good...
Vintage-Nut JAN 03, 11:51 AM

quote
tested the ECM



If the ECM relays are good, check the wires from the fuses to the injectors AND from the injectors to the ECM {see the schematic in the link}

EDIT - The ECM relays are 'ground' - if you have 12v at the injectors; try to ground the injectors on the block...

[This message has been edited by Vintage-Nut (edited 01-03-2025).]

Dennis LaGrua JAN 03, 12:01 PM
Check for 12V on the fuel injectors with the key in the on position. If there is no voltage there then the problem is probably in the harness or a remote chance that the ECM is bad. Also check the wiring on the connectors at the ECM. Mice love to chew on those.

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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 "

1985 Fiero GT JAN 03, 12:36 PM
"runs until the prime shot is burned", what's the fuel pump doing? Status of the relay and pump as it's "running"? I don't see how the ECM can prime the pump but not turn it on when the engines going, but I also can't see how the ECM can fire the injectors for a second or two, then quit. As far as I know the injectors do not prime, only the fuel pump, the injectors only inject if the engine is actively turning, and the cold start injector only injected when it is actively cranking on the starter, and I doubt it would fire off on the cold start injector. Try manually enabling your fuel pump via the obd1 connector, there's a pin that you connect to +12v (cigarette lighter) and it turns the pump on, you should hear the pump, it should keep running as long as it is powered, see if you can start and run the car like that, if so, something funny is happening in the wiring.
Boozeman JAN 03, 12:58 PM
Thank you for the ideas, gents - I appreciate the help! We'll run these traps this evening, and I'll report back what we find...
Dennis LaGrua JAN 03, 02:15 PM
Yes, backing up a bit. First step as pointed out, measure the fuel pressure. Could be the pump

------------------
" 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 "

Boozeman JAN 03, 03:35 PM
Fuel pump is priming and holding pressure. Pump was replaced recently. Thanks!
1985 Fiero GT JAN 03, 03:54 PM

quote
Originally posted by Boozeman:

Fuel pump is priming and holding pressure. Pump was replaced recently. Thanks!



And does the pump keep running when you attempt to start?