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 PERFORMANCESYSTEMENGINE CONTROLS - SYSTEM/COMPONENT TESTSEXHAUST GAS RECIRCULATION (EGR)PULSE WIDTH MODULATED EGR VALVE
1990 Pontiac Firebird Formula, 5.0 F, Automatic, 4L60/MD8
Pulse Width Modulated EGR Valve
1990 Pontiac Firebird Formula, 5.0 F, Automatic, 4L60/MD8SECTION Pulse Width Modulated EGR Valve
- Place transmission in Park or Neutral. With engine at idle and at normal operating temperature, push up on EGR valve diaphragm. Engine RPM should drop. If engine RPM did not drop, clean EGR valve and passages.
- Check EGR valve movement with engine RPM change from 2000 RPM to idle. If EGR valve moves with RPM change, check Park/Neutral switch adjustment or open circuit. If EGR valve did not move, ground ALDL test connector. If EGR valve moves now, EGR valve is functioning properly. If not, go to next step.
- Turn engine off and disconnect EGR solenoid connector. Connect 12-volt test light between EGR solenoid connector terminals. Turn ignition on and ground ALDL test connector. Test light should flash repeatedly.
- If test light flashes, check vacuum to EGR solenoid at 2000-3000 RPM. If engine does not use a vacuum regulator, at least 7 in. Hg should be present at solenoid. If engine is equipped with a vacuum regulator, 2-10 in. Hg should be present.
- If vacuum is greater than 10 in. Hg, replace regulator. If vacuum is less than 2 in. Hg, vacuum at solenoid is okay. Check EGR solenoid connections and/or faulty EGR solenoid.
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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.