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 MANUALSJEEP1987WAGONEER BASE, 4.0 M, AUTOMATICREPAIR AND DIAGNOSISENGINE PERFORMANCEIGNITION SYSTEMIGNITION SYSTEM - SOLID STATETESTINGCONTROL UNIT & SENSOR
1987 Jeep Wagoneer Base, 4.0 M, Automatic
Control Unit & Sensor
1987 Jeep Wagoneer Base, 4.0 M, AutomaticSECTION Control Unit & Sensor
- Disconnect coil wire from distributor cap. Using insulated pliers, hold the end of the coil wire 1/2" from the engine block. Turn ignition on.
- Disconnect 4-wire connector from control unit. Watch for spark as connector is separated. If no spark occurs, proceed to step 6). If spark occurs, turn ignition off and go to step 3).
- Attach ohmmeter between the Orange and Violet wire terminals "D2" and "D3" of harness connector. Ohmmeter reading should be 400-800 ohms. If reading is correct, proceed to step 6). If reading is not correct, disconnect and reconnect 3-wire connector at the distributor. If ohmmeter reading is now correct, proceed to step 7).
- If reading is still incorrect, separate 3-wire connector at distributor. Attach ohmmeter leads between Orange and Violet wire terminals "B2" and "B3" of distributor connector. If resistance is 400-800 ohms, repair harness between 3-wire and 4-wire connectors. If reading is still out of specification, replace pick-up coil.
- Attach ohmmeter leads to negative battery terminal and Black wire terminal "D1" in harness connector. Ohmmeter should read less than .002 ohms. If ohmmeter reading is okay, recheck system starting at step 3).
- If continuity exists, check for bad ground (ground screw in distributor-to-Black wire terminal "D1", ground cable, or distributor-to-engine block).
- Turn ignition on and connect voltmeter to harness side of 4-wire connector Orange and Violet wire terminals "D2" and "D3". Voltmeter reading should fluctuate while cranking engine.
- If no voltage fluctuation occurs, check for defective trigger wheel, distributor shaft not turning, or missing trigger wheel retaining pin (shaft turning but not trigger wheel).
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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.