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 MANUALSPONTIAC1983GRAND PRIX BASE, 5.0 HREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCEIGNITION SYSTEMIGNITION SYSTEM - V8TESTINGEST EMISSION SYSTEM CHECK
1983 Pontiac Grand Prix Base, 5.0 H
Est Emission System Check
1983 Pontiac Grand Prix Base, 5.0 HSECTION Est Emission System Check
- With shift lever in "P" (auto. trans.) or Neutral (man. trans.), run engine at fast idle and note timing change as test terminal is grounded. If timing changes, system is operating properly.
- If timing does not change on vehicles equipped with manual transmissions, proceed to step 3. If timing does not change on vehicles equipped with automatic transmissions, let engine return to idle and place transmission in "D". Note timing change as test terminal is grounded. If timing changes, system is operating properly.
- If no change in timing occurs (all models), check voltage at output of MAP (Manifold Absolute Pressure) sensor or vacuum sensor as vacuum hose is removed and reinstalled. If no change occurs, problem is in the vacuum or MAP sensor circuit. If voltage output changes, proceed to step 4.
- Disconnect park/neutral switch and recheck for timing change. If timing changes, problem is either an improperly adjusted or faulty park/neutral switch. If timing does not change, check for grounded wire from terminal "H" of ECM to park/neutral switch. If wire is not grounded, replace 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.