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 MANUALSPONTIAC1991TRANS SPORT SE, 3T40/MD9REPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROLS - BASIC TESTINGA-3, NO-START DIAGNOSISENGINE CONTROLS - BASIC TESTINGFUEL SYSTEM (TBI)
1991 Pontiac Trans Sport SE, 3T40/MD9
Fuel System (TBI)
1991 Pontiac Trans Sport SE, 3T40/MD9SECTION Fuel System (TBI)
- Before checking fuel system for a no-start condition, check ignition for adequate spark. Check for proper fuel pump pressure (9-13 psi) and capacity (one pint in 30 seconds). See A-7, BASIC FUEL SYSTEM CHECKS (GASOLINE).
- Crank engine, and watch for injector spray. If injector spray occurs, go to step 5). If no spray occurs, disconnect injector harness, and check for battery voltage at harness.Battery voltage should be present on one injector terminal.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 on only one terminal, connect injector test light (also called a "node" light) to injector harness. Crank engine, and note light. If light flashes, check for stored ECM codes. See DIAGNOSTIC CIRCUIT CHECK. If no codes are present, refer to HARD START symptom in TESTS W/O CODES article in this section. If light does not flash, momentarily touch test light from battery voltage to ECM RPM reference terminal (circuit No. 430).
- 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 or injector drive (ground) circuit. If wiring is okay, replace faulty ECM. Prior to replacing ECM, check ECM power and ground circuits.
- If injector spray occurred while cranking engine, disconnect injector harness,and crank engine.If injector spray or leakage occurs, a no-start condition could be caused by excessive fuel being delivered during cranking. Repair faulty injector or injector seal. If no spray or leakage occurs, refer to HARD START symptom in article TESTS W/O CODES in this section.
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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.