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.
Special Diagnostic Tools
The computerized engine control system is most easily diagnosed using a "Scan" tester, however, other tools may aid in diagnosing problems if a "Scan" tester is unavailable. These tools are: a tachometer, a dwell meter, test light, ohmmeter, digital voltmeter with 10-megohm impedance (minimum), vacuum pump, vacuum gauge, fuel injector test lights (TBI and PFI) and 6 jumper wires 6" long (one wire with female connectors at both ends, one wire with male connector at both ends and 4 wires with male and female connectors at opposite ends). A test light, rather than a voltmeter, must be used when indicated by a diagnostic chart.
When engine is at operating temperature and idling, dwell meter needle should vary between 10-50 degrees. This indicates closed loop operation. Before engine reaches operating temperature, dwell should be fixed between 10-50 degrees, indicating open loop operation. If after reaching normal operating temperature dwell is fixed between 10-50 degrees, less than 10 degrees or more than 50 degrees, refer to appropriate CHART A - DWELL FIXED diagnostic chart for that system.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- β’ You smell fuel, burning insulation, or see smoke.
- β’ Brakes feel soft, pull hard to one side, or make grinding noises.
- β’ The engine overheats, stalls repeatedly, or misfires under load.
- β’ You are missing required tools, torque specs, or safe lifting equipment.
- β’ You are not confident in the next step or safety outcome.