'86 Comanche Long bed, Slow build...


12/13/17 Update: I know Photobucket issues cause most of you not to be able to see the pictures. There IS a workaround for some browsers!! Search "photobucket hotlink fix". You'll see apps for Firefox and Chrome. If you're not using one of those two browsers, you need to start. Click the "install" button and voila, pictures show up!

Well, I've been debating whether to post some build details and ideas here, or on some sort of Jeep forum... I decided that this is the place, at least for now, since I don't belong to any Jeep forums...

I have been lusting after a Comanche for quite a while, and finally bumbled onto an '86 last summer for $700. It is an '86, and the 2.8L has 225k miles on it, and wasn't running right. (Starts great, but runs worse and worse as it warms up.) My theory was that it busted a crank, or has split pistons or something. Guy says it started running like crap during an emissions test in CO. It's a Colorado vehicle at least most of it's life, so there is little rust, which was the clincher for me! I drove it about 25 miles home at 35mph because that's pretty much as fast as it would go.

Based on firewall mods needed to put a 4.0L in an '86 Comanche, I decided almost immediately that the easiest engine swap was a 3.4L from a '94/95 Camaro. Of course I wanted Fuel Injection too, and I found an engine on Craigslist that would come with all accessories, harness, and computer for $300. I dumped the 3.4 in the bed and let it sit for almost a year while I moved.

I considered for a short while finding a 4.8L V8 and tossing that in, but then I'd need lots of expensive adapters, a new trans and whatever else goes with that, and a big radiator, exhaust, etc... The Comanche is light, so I'm hoping for a little better fuel economy from the 3.4L anyway!

I prepped the 3.4L by pressure washing it and identifying all needed wiring connections for the GM computer, and labeling them.

I also put some stuff back together that the idiot I got if from started to take apart for no reason. (Lots of missing bolts that I had to get from the junkyard...) What are some people thinking?? I stripped off the air injection tube, but left the EGR for now so I don't need to reprogram the computer. Here's the 3.4L ready for motor mount transfer...

Time to pull the 2.8L out of there!! Look at all that emissions junk!! According to the label, this is a "high altitude" emissions truck. Not sure if that means it's more like CA, or FED, but at least it doesn't have a computer controlled carb!

And its out!!

Look what I found in the bellhousing!!

More in a bit...
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Well, I pulled the motor mounts off the 2.8 and the driver's side bracket bolted right onto the 3.4L. On the pass side, I was not so lucky... First, the knock sensor on the 3.4L is right in the way of the 2.8 motor mount. Swapped it for the block drain plug lower and farther back on the block and resolved that problem. (It should still work fine from what I've read.)
(You can see the plug where the knock sensor was, just left of the top of the motor mount, and the knock sensor in it's new location at the lower back of the block, behind what I think is the crank position sensor.)

Then I realized that the A/C compressor was ALSO in the way. Evidently the Camaro motor mounts are lower and farther back on the block than the Jeep mounts. (I don't have them, but I may watch for the right one to see if I can use it instead...) I pulled the A/C compressor and its rear bracket, and the mount finally bolted up.
(Compressor is about 2" too long. :( )

Then I realized that the Camaro flywheel is a deep, dished design, whereas the 2.8L flywheel is flat, like you normally see. Mind you, it's not heavier, just dished and hollow. Not sure why GM did this...
(Jeep 2.8L flywheel still on the engine, thick Camaro flywheel in my hand.)

But I couldn't use the '86 2.8L flywheel because it's externally balanced. I could either have it machined and re-balanced, or get a later 2.8L flywheel for an S-10. (They switched to internally balanced somewhere around '88) Since a new one was only $60, I ordered it up! I'm hoping that the Comanche clutch will bolt up, as it looks fairly new.

For now, I'll just run it without the A/C pump. The truck is missing all the rest of the underhood A/C stuff anyway. If I get excited about A/C, perhaps I'll be able to figure out a pump that will fit and work and get it all plumbed up.

Next up: cleaning up the under hood wiring mess...
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Root Moose

Expedition Leader
Oh man... just sell the the 3.4 and get a 4.0! Use it as an excuse to get a ready built stroker and don't look back. ;)

My MJ came from Colorado as well. It's so nice when everything comes apart without applying heat or extreme measures. Little bit of wire wheel on the floor and some primer and my MJ is ready for top coat inside and out. Such a change from what I'm used to.


Expedition Leader
I too have a soft spot for MJ's, so I will be watching to see where this one goes.



Already have the 3.4L so not doing a 4.0L. (My TJ is waiting for me to get the 4.5L stroker project underway.) This truck is just going to be a driver!! I'm hoping it'll get good mileage, and since it weighs less than a Camaro, it should get around quite well! I have a big truck if I need to get more done. :)

Flywheel came in a few days ago and it all bolted up, using the clutch that was in the Comanche on the 2.8L, so the engine is ready to go back in!

Ripped all the split loom off the underhood wiring and started sorting out what I needed and what could go.

Looks like the Comanche barfed up it's dinner when I was done...

Much less mess underhood, and I know what everything that's left does.

Used a BlueSea fuse box and a distribution block from an early 90's Chevy truck. Added relays for switched ignition and fuel pump up by the fuse block, and fan control down in front.

Just about as far as I can go without the engine and harness in place, so time to toss the 3.4L in!!

About time for another junkyard run... I'm planning to use a 2-speed Taurus fan, with low being on anytime the engine is running, and high controlled by the computer. Saw a new radiator in a junker last time I was there, so I'll be picking that up too! And an instrument cluster with a tach to see if I can get that working. (Hopefully it will be OK with the GM tach signal...)

Once it's all together and working, I'll put it back in split loom and it should look pretty clean.
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I too have a soft spot for the Manche. I want to find one once we get out to New Mexico. Awesome truck and its a Jeep. Great job so far and will follow the thread.
about a month ago, there was a wildernest for a longbed MJ up on the Reno CL, not sure if its still available. also, check in over at comancheclub.com!


Took last week off as I was out of town, but I managed to drop in the 3.4L before I left... Back to it now!!

I finished the important wiring last night. Still need to swap in the XJ fuel pump that I bought and run a 12v wire for the pump down from the relay. Then put the starter in, hook up the fuel lines, toss in the battery, and see if it runs!! If it does, and doesn't sound like I paid $300 too much for it, I'll get it an idler and serp belt, put a radiator in it, and wire up the rest of the non-essentials. (Gauges, CEL, Clutch and brake switches, and cruise control)

Time for a junkyard run at lunch today too!! I love the junkyard here!!! :)
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I have fuel!!! (and a leak...)

Fuel pump is in after slightly re-bending the hard line so the pickup was on the bottom of the tank. (It was for an XJ. Couldn't find one for the MJ, but they're close enough to work...) I found out that the factory wiring back to the tank connector already had the 12v fuel pump wire in it. Traced it to the fuseblock/firewall bulkhead, where it didn't have a wire coming out under the hood. Took the bulkhead apart, swapped over a heavy wire that was no longer used (even the right color!!) and hooked it to my fuel pump relay. Aside from the relay, the factory wiring now runs the pump!! Not sure it was easier than running a new wire, but it's certainly cleaner!!

Got all lines hooked up and cycled the key a few times. Pump runs, gauge works!! Just a little dripping from the crusty old rubber fuel lines under the truck. Guess I'll replace them both and be done with it, since the fuel pump stays in no matter what. Only need about 14" of hose, since I'm using the factory hard lines for most of the run.

Tomorrow: Starter, battery harness, nuts on the down pipes and see how it runs!! (Oh, and I suppose I'll have to work too...) If it seems to run OK, then I'll hook up the rest of the wiring and put in a radiator. Junkyard trip today at lunch got me a radiator that at least should hold coolant and throttle cables from a V6 camaro and a V8. (The V6 cable was really short, so I think I'll have to use the V8 cable...) Also got the cruise cancel switch for the clutch. Engine controller uses it as "clutch anticipate" too. I'm putting cruise in it anyway, so I'll hook it up. :)

Not gonna lie, I'm going to be pretty excited if it fires and runs decently!! :wings:


Haven't updated in a while, but I've been making progress. Exhaust is now back together with one manifold stud having been replaced by a long bolt that I cut the head off. Almost all the wiring is done, with only the oil pressure sender, OBDII connector, and check engine light left. The A/C wiring is getting tucked into the harness for now. I ordered the A/C pump delete plate and idler today, but it won't be in for a few days, and I'm out of town for the weekend.

My junkyard radiator leaked, so I took it back and got a gauge cluster with the tach. Plugged it in and it works, and even reads correctly!! It even matches the Comanche cluster exactly, so I'll swap in the speedo to retain actual miles just for fun. A new aluminum radiator has been ordered and should be here tomorrow. Should have it up and running properly early next week!! Just moving it around (With no throttle cable until yesterday) it's fairly apparent that this little motor has quite a bit of idle torque. Should be really easy to drive!!

The bad: My craigslist "runs great" 3.4L seems to have a bit of a miss. I checked all the plugs (Bosch Platnums!!) and they all look about the same, which is to say a little black, but not bad. One may have been a tiny bit wet... I'm hoping it's just a stuck injector, so I poured some seafoam in the tank and I have been starting it and letting it run for 30 or so seconds a few times a day. It definitely started hard, and had some stuck injectors when I first got it going, so I'm hopeful that's all it is. I'll diagnose it properly once it has coolant and a serp belt... hard to learn much in the little bit that I'm comfortable running it with no coolant.

I'm pretty excited to soon be done with the engine swap and wiring work and get to do some paint and bumpers!! It's getting painted Rustoleum Sand instead of white. We'll see how I like it. Or how my fiancee likes it, since she'll be driving it the most. (It was her idea to paint it sand...)

Stay tuned!!



Well, we cut a camping trip short this weekend thanks to some rain, so I got to work on finishing up the wiring Sunday. Still have a few wires to run, but done for now. Wires to run are for clutch "anticipate" and A/C trigger (which I'll use for high idle eventually...) and the cruise wires when I put in the cruise module.

All buttoned up in conduit and clipped into place.

Also took off the old sawblade ZJ wheels and 30x9.50's and put the 235/85's on it. Funny enough, these tires look tiny on my TJ, but they're huge on the Comanche... I'll bump it up 1" or so and that should make it look quite a bit better. They rub the front control arms at full lock, but not enough for me to worry about it. :)

Sorry about the crappy neighborhood shot at high noon... You get the idea though. :)

I drove it around some more, and I can't get the clutch to bleed out right, or it's messed up somewhere... It releases right on the floor, and once the truck warms up, then it sometimes hangs a little. Master and slave both appear to have been replaced at some point in the past, so I'm thinking they're OK but I have about 2" of mostly dead travel when I initially step on the clutch that won't go away no matter how I bleed it. May replace the Master, as it's cheap and easy. If that doesn't fix it, then I'll put a slave on it, and if that doesn't work, then I guess I'll pull the trans and check the pivot stud and fork. (I had a broken fork on an old '86 XJ that I bought, but I looked at this one and didn't see any cracks... )

Need to figure out an air filter for it next. Then perhaps find a good front bumper and get a windshield in it so we can drive it!!
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Root Moose

Expedition Leader
Lookin' good!

For the clutch I've always found getting a helper to help bleed it similar to a brake line gets it half way... then close it and pump the hell out of it for a minute or two from the pedal and it works fine after that. That was on an S2000 and a old GM6 Subaru. I dunno, just seems to have worked in the past.

For the air box use this as a good excuse to install an Donaldson of some flavour?


Hahah I looked at Donaldson's... I HAD one in my collection of junk forever ago, but tossed it because I couldn't figure out what I'd ever use it for... now I'd have to pay $100 for one... Dang it!! I need to move the washer reservoir and coolant bottle to put a Donaldson on under the hood on the driver's side. I think for now, it'll just get an elbow and an open element cone filter for cheap. Something better later, when i don't have so many other things to do to it...

I've pumped the crap out of the clutch. It still sucks. i think it's bled fine, and i'll just have to start replacing parts until I figure out what's wrong.

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