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 MANUALSFORD1991CAB & CHASSIS 5.8 H, AUTOMATICREPAIR AND DIAGNOSISENGINE PERFORMANCESYSTEMENGINE CONTROLS - TESTS W/CODES - 7.5LQUICK TESTCOMPUTED TIMING CHECK
1991 Ford Cab & Chassis 5.8 H, Automatic
Computed Timing Check
1991 Ford Cab & Chassis 5.8 H, AutomaticSECTION Computed Timing Check
Turn ignition off and wait 10 seconds. Using jumper wire or test equipment, activate KOER SELF-TEST. Start engine and check for the following:
- If engine starts and stalls, or stalls during self-test, go to TEST S, step 1).
- If Code 98 or 998 is displayed, it indicates EEC-IV system is operating in Failure Mode Effects Management (FMEM). Vehicle cannot be diagnosed in KOER SELF-TEST; rerun KOEO SELF-TEST.
- Check computed timing after the last service code has been displayed. The timing will remain fixed for 2 minutes after the last code has been received, unless self-test is deactivated.
- Computed timing, at the crankshaft, should equal the base timing (see vehicle emission decal) plus 20 degrees BTDC. This timing may vary 3 degrees (+/-). If computed timing is within specification, perform KOER SELF-TEST. If timing is not within specification, go to step 2) of TEST PC (vehicles with EDIS), or step 2) of TEST PA (vehicles with TFI).
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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.