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.
Primary Circuit Test (Closed Bowl Distributor)
- Disconnect terminal "S" at starter relay to allow testing of ignition primary circuit without cranking motor. Ensure ignition is off. Push down on connector tab and disconnect harness connector from TFI module. Ensure TFI module connector is not corroded or swollen. Repair or replace connector as necessary.NOTE: If connector is damaged or has broken tabs due to misuse, replace connector. A loose or damaged connector may cause ignition signal faults during KOER operation.
- Use a straight pin or terminal spade from an old TFI module to probe connector. Avoid ground contact, between straight pin and ground, during testing. Using a DVOM, turn ignition on and measure voltage at following vehicle harness connector terminals of the cowl mounted TFI module: See Fig 1
.
Key On Engine Cranking (KOEC)
- No. 2 (Coil Negative)
- No. 3 (Power/Run Circuit)
- No. 4 (Start Circuit - Non-CCD Systems)
Key On Engine Off (KOEO)
- No. 2 (Coil Negative)
- No. 3 (Power/Run Circuit)
If approximate Battery Voltage (VBAT) is not present at these terminals, repair open circuits in wiring harness as necessary. See appropriate wiring diagram in WIRING DIAGRAMS at the end of this article.
- If battery voltage is as specified, check module ground circuit. With TFI module disconnected and KOEO, measure voltage at terminal No. 6. If voltage is greater than .5 volt, ground circuit has high resistance or is open. Repair as necessary.
- Ensure ignition is off, disconnect distributor connector. Turn ignition on. With DVOM set on DC voltage scale, connect positive (+) lead to terminal No. 8. Connect negative (-) lead to distributor or engine ground. See Fig 1 .
- Cycle ignition switch between ON and START positions. Battery voltage should be present in both positions. If not, service or repair circuit as necessary. If okay, go to next step.
- Use a DVOM to check ignition ground circuits continuity. Measure resistance between distributor base and terminals No. 2 and No. 6 at distributor connector. If resistance at each terminal is less than 3 ohms, circuit is okay. If resistance is not less than 3 ohms, repair ground circuit as necessary.
NO RELATED
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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.