1985 Jeep Pickup J20FACTORY OEM SERVICE PROCEDURE

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).
Factory Service Tools

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.

Shop Manual-Ready ToolsCompare Repair QuoteQuote Shield Pro

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.

Rather have a pro handle this?

A certified mobile mechanic comes to your home or office. They bring the tools, you stay comfortable. No tow truck, no waiting room, no surprises.

Comes to youSame-day available12-month warranty
Get a Free Quote

No obligation. See pricing before you book.