Symptoms
Hard starting, rough idle, hesitation and poor fuel economy, which Jeep-CJ.com's write-up blames on the factory Duraspark.
The fix, step by step
- Start with a cap, rotor, plugs and wires.
- For the HEI swap, use a 1976–82 GM inline-six HEI with an AMC V8 drive gear.
- Mark No. 1, swap the distributors and feed the HEI from the constant-12 V firewall wire, not the resistor coil feed.
- Gap the plugs to .045 in (firing order 1-5-3-6-2-4) and set the timing with a light; many owners run about 8° BTDC.
- Trucks with the feedback ECM need it bypassed first.
Tools & part numbers
- Timing light
- volt meter
- soldering iron
- plug gapper
Where to buy the parts
Crown J8128445 distributor pickup, 1977–90 CJ 4.2LQuadratec ↗Amazon ↗
Performance Distributors DUI distributor, 1972–90 CJ 232/258Quadratec ↗Amazon ↗
Distributor cap, 1984 Scrambler 4.2LRockAuto ↗Amazon ↗
Spark plug wires, 1984 Scrambler 4.2LRockAuto ↗Amazon ↗
Hunting a used or discontinued part? Search eBay Motors for Jeep CJ-8 Scrambler parts →
Rated for a competent home mechanic with a decent tool kit. Confirm torque figures, fluids and procedures against the factory service manual for your VIN, support the truck on stands rather than a jack, and work at your own risk (disclaimer). Some parts links are affiliate links, which pay us a small commission at no cost to you.