Pristine 1986 Jeep 4.2L CJ-7 With Engine Damage

[Old Soldier]

Moses, I am energized by your projects/knowledge and want some advice which I think will be simple for you.

I have an 86 CJ-7 since 90.  4.2, 5-speed, Dana 44 rear, A/C, 4” lift, Xfer lowered, 4.10 gears, ltd slip front. 38,000 miles.

Parked/stored 98-2010 until retired from Army. Then Mom drove Florida to Texas on low/no oil. Heard her coming before I saw her. Broke my heart and I put it in the barn.

Engine still ran with knocking sound.

The obvious question…

What do you recommend?

 

 

[Moses Ludel]

Old Soldier...Given the pristine condition of the Jeep and its value in the lightly modified condition, I would consider a restoration rebuild.  If you want to modernize the engine, a 4.0L MPI (1991-94 prototype) engine swap would not be a dramatic chore.  If your engine's crankshaft can be salvaged, the crank and rods could make a 4.6L stroker motor out of a 4.0L engine.

The kicker here is EFI.  You need to get a donor engine (1991-94 distributor type engine is the easiest route) and get the engine peripherals, computer ("60-way"), wiring harness and an appropriate fuel pump and filter.  Then there will be time spent sorting out wiring and mating the EFI harness to your chassis.  This has been done many times but is not simple.  It takes automotive electrical savvy, time and the 4.0L wiring harness.  The electric fuel pump is computer driven and must be wired accordingly as part of the EFI system.

An earlier and faster solution, which I address in my Jeep® CJ Rebuilder's Manual 1972-86 (Bentley Publishers), was the use of a Mopar® EFI Conversion Kit, which was actually designed for 1981-90 4.2L engines like yours.  The unfortunate part is that the complete kit is no longer available and last sold for around $2,700.  HESCO still offers many service replacement parts and workarounds for 4.0L conversions at:  https://hesco.us.  (Enter "HESCO" in the forums' search bar for more insight.) Unless you use the donor engine's EFI/MPI system, computer and wiring harness, this is a cost-prohibitive approach. 

Today, I would seriously consider a Chevrolet LS V8 conversion with parts from Advance Adapters.  If you can do the fabrication work or have access to a shop that can, it would be no more difficult, and less expensive, to do a V8 swap than to rebuild and swap a 4.0L Jeep EFI/MPI inline six into your CJ chassis.  Low mileage, recycled LS engines with wiring and ECM are abundant, and a Painless wiring harness can make this conversion straightforward.

Personally, I would do the restorative approach given the low mileage on your 4.2L engine and chassis.  The BBD carburetor is fully functional in emission legal form; we went over the Rubicon Trail in CJ and YJ 4.2L models with stock carburetion.  I address the BBD carburetor rebuild and restoration in my book.  This is the most straightforward way to get the Jeep back on the road.  (The engine would require removal to access the crankshaft.)  Parts are readily available, and all automotive machine shops are familiar with the 4.2L engine rebuild.  It's possible that a lighter rebuild will work if only the crankshaft is damaged.  A teardown would confirm.

Let's discuss this further if you have questions or ideas...

Moses

[Old Soldier]

Thanks a million for the quick response. I gotta say I’m not a hp hound. Loved it like it was, got me in & out of many jams. But I’m sure you know that ignition timing drove me nuts. I couldn’t agree more with engine rebuild/restore. What’s your top choice for fuel/ignition on 4.2? 
 

I did put Borla header on it as well. My rookie opinion is rebuild, gm hei distributor and carb. 
 

Thanks again
 

[Moses Ludel]

You're welcome, Old Soldier...I would do a Howell EFI conversion, simple and compatible with a conventional ignition.  Yes, I would do the GM/HEI style distributor, though of course it needs to be an AMC/Jeep 4.2L version.  (The distributor drive gear of the GM 230/250/292 inline six distributor is different than an AMC drive gear.)  There are several aftermarket HEI style distributors available for the AMC/Jeep 4.2L six.  They range from "cheaper" versions to the DUI unit.

Howell is a bolt-on system with a 50-State legal version of the kit.  It meets emissions and offers a horsepower gain, more torque and a nice complement for the Borla header.  If you're at Texas and have trips planned to the Colorado 'Fourteeners, the Howell EFI, like other 02 driven systems, will compensate for altitude.  This is the most significant gain with the package.  Peak power and efficiency may not be the same as the Mopar MPI/EFI Conversion Kit, but you would have a reliable system built around common GM TBI replacement parts.

Moses