Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSPONTIAC1990FIREBIRD FORMULA, 5.0 F, AUTOMATIC, 4L60/MD8REPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCETESTING & DIAGNOSISENGINE CONTROLS - BASIC TESTINGNO START DIAGNOSISNO START - ENGINE CRANKS OKAY (PFI WITH IDI)FUEL SYSTEM
1990 Pontiac Firebird Formula, 5.0 F, Automatic, 4L60/MD8
Fuel System
1990 Pontiac Firebird Formula, 5.0 F, Automatic, 4L60/MD8SECTION Fuel System
- Prior to checking fuel system for a no-start condition, check ignition for proper spark. Check for proper fuel pump pressure (40-47 psi) and capacity (one pint in 30 seconds). See BASIC FUEL SYSTEM CHECKS in this article.
- Disconnect injector harness. Turn ignition on and check for battery voltage at each injector harness. Battery voltage should be present on one of the injector terminals. If battery voltage is not present, check for blown injector power fuse. If battery voltage is present on both terminals, check for wires shorted to one another.
- If battery voltage is present to each injector, connect injector test light to injector harness. Crank engine and note light. Repeat on other injector connectors. If light flashes, check for stored ECM codes. If no codes are present, refer to HARD START symptom in TESTS W/O CODES article.
- If light does not flash, access IDI ignition module harness connector. Disconnect connector and momentarily touch test light from battery voltage to ECM RPM reference wire (circuit No. 430) of module harness. Each time test light is removed from ECM RPM reference terminal, injector test light should flash. If test light does not flash, check for open in RPM reference wire, injector drive (ground) circuit or replace faulty ECM.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.