SYMPTOM DIAGNOSIS
Symptom checks cannot be used properly unless problem occurs while vehicle is being tested. To reduce diagnostic time, ensure steps in appropriate SELF-DIAGNOSTICS article were performed before diagnosing a symptom. Following symptoms are available for diagnosis.
- Will Not Start (Cranks Okay)
- Difficult Start (Cranks Okay)
- Engine Surges
- Rough Or Unstable Idle
- Excessive Fast Idle
- Engine Stalls
- Engine Lacks Power
- Engine Misfires Or Hesitates
- Afterburn In Exhaust System
- Poor Fuel Mileage
- Detonation Or Knocking
- Fails Emission Test
FAILS EMISSION TEST
- Ensure engine is at normal operating temperature.
- Check crankcase for fuel contamination.
- Ensure base timing is correct.
- Check for correct PCV valve operation.
- Check EGR system for correct operation (2.8L).
- Check Mass Airflow (MAF) sensor.
- Ensure air intake system is not restricted.
- Check vapor recovery system operation.
- Check Engine Coolant Temperature (ECT) sensor operation.
- Check Heated Oxygen Sensor (HO2S) output voltage.
- Ensure fuel system pressure is correct.
- Check fuel tank filler tube for tampering of restrictor. If tampering has occurred, check catalytic converter for lead contamination and exhaust system restriction.
- Check for poor quality fuel containing insufficient cleaning additives.
Note. Prolonged use of poor quality fuel can cause injector clogging and carbon build-up on intake system.
INTERMITTENT PROBLEM DIAGNOSIS
Intermittent trouble code testing requires duplicating circuit or component failure to identify problem. These procedures may lead to computer setting a trouble code which may help in diagnosis.
If vehicle does not produce trouble codes, monitor voltage or resistance values using a DVOM while attempting to reproduce conditions causing intermittent fault. A status change on DVOM indicates a fault has been located.
Use a DVOM to pinpoint faults. When monitoring voltage, ensure ignition switch is in ON position or engine is running. Ensure ignition is in OFF position or negative battery cable is disconnected when monitoring circuit resistance. Status changes on DVOM during test procedures indicate area of fault.