LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Jeep >> 1985 >> Pickup J20 >> Repair and Diagnosis >> Engine Performance >> Ignition System - Solid State >> Testing >> Control Unit & Sensor Check
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Control Unit & Sensor Check

  1. Disconnect high tension coil wire from distributor cap. Attach a modified spark plug to coil wire (side electrode of plug cut off and ground wire attached to side of plug casing). If plug is not available, hold coil wire 1/2" from engine block, using insulated pliers.
  2. Turn ignition switch "ON" and disconnect 4-wire connector from control unit. Watch for spark at modified spark plug, as connector is disconnected. If sparking occurs, proceed with next step. If no sparking occurs, proceed to step 6).
  3. Turn ignition switch "OFF", and disconnect J2 connector at ECU. Connect an ohmmeter between the MCU wire terminals "3" and "5" of harness connector. Ohmmeter reading should be 400-800 ohms. If reading is correct, proceed to step 8). If reading is not correct, proceed to next step.
  4. Disconnect and reconnect the 3-wire connector at the distributor. If ohmmeter reading is now correct, proceed to step 8). If reading is still not correct, proceed to next step.
  5. Disconnect 3-wire connector at the distributor and connect ohmmeter leads between the Orange and Violet wire terminals "B2" and "B3" of distributor connector. If reading is now 400-800 ohms, repair harness between 3-wire and 4-wire connectors. If reading is still out of specifications, replace sensor in distributor.
  6. With ignition switch "OFF" and 4-wire connector disconnected, connect ohmmeter leads to battery negative terminal (ground) and Black wire terminal "D1" in harness connector. Ohmmeter reading should be nearly zero (less than .002 ohms).
  7. If ohmmeter reading is OK, recheck system starting at step 3). If reading is above specifications, check for the source of the bad ground, (ground cable resistance, distributor-to-engine block resistance, or ground screw in distributor to black wire terminal "D1").
  8. With ignition switch "ON" and voltmeter connected to harness side of 4-wire connector Orange and Violet wire terminals "D2" and "D3", crank engine. Voltmeter reading should fluctuate.
  9. 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).
scientia non olet · About LEMON Manuals