First MJ(s)

[Awesome]

A few years ago I was talking to a co-worker about an MJ he had in his field that he'd driven as a teenager until he finally crashed it enough that it didn't run anymore. It was a kid's farm toy and he beat the ever living snot out of it. He didn't really want to scrap it, so he sold it to me for scrap price.

 

$250 got me my first MJ. Plan is (was) to turn it into a DD for my oldest daughter's first truck.

 

 

 

That's as it sat when I picked it up. I was pretty excited because it was almost completely rust-free. 

 

 

The bed ended up being totally destroyed. Completely rusted through and so beat up it wasn't salvageable.

 

 

And so it's basically sat in that same spot for the last couple of years. Last year when the weather was nice enough to work on it, my mom's cancer came back and killed her. So I didn't get a chance to really work on the MJ project last year.

 

So this year, a member on the JeepForum once again reminded me that he also had an MJ that he was willing to let me have. So I saved some funds up, got a buddy to go with me, and drove the 1200 miles one direction to go pick it up.

 

 

 

Which directly leads to my current problem:

 

 

Ok time for stats:

 

MJ #1: 1988 242ci, AW4, NP231 4x4 shortbed Pioneer with air conditioning. ~80,000 miles. My daughter and I DID end up getting it running, but then got bogged down with fixing things. It never had enough working parts on it at once to actually drive it.

 

MJ #2: 1986 AMC150, AX-5, NP207 4x4 longbed "Custom" or "X" model, not sure which. 187,000 miles. It has no air conditioning but does have a sliding rear window that I am not convinced is stock. It also appears to have a factory headache rack, which is so 80s that I LOVE it. It's definitely staying on the truck, and probably getting added to a rollcage.

 

MJ #2 is waiting on a new key cylinder to show up so we can check compression and see if it's worth getting it running. It came without keys, no front bumper, no driver's side window, no passenger side mirror and a cracked header. It's also missing some trim pieces and the headliner. It has some pretty bad rust spots under the floor near the rockers. Those will probably get replaced or patched, but we're going to tear the interior out first as the original vinyl flooring is pretty nasty. I will assess the floors better once that's done.

 

MJ #1 is now missing a steering box, as I had to replace my wife's TJ's box after my wife destroyed hers. Need to send it to Red Head for a rebuild but haven't done it yet. I was in the middle of upgrading the brake booster when my mom's cancer came back, so it currently has no brakes. It has one tiny rust spot on the passenger side footwell. The 4.0 does run, but the motor mounts were totally shot and it was banging around so I am still not sure exactly how well it runs.

 

Thus begins my documentation here among people who understand the rarity of Comanches.

Also I need motivation, I tend to get bogged down in the details.

 

A few edits to add clarity:

The '86 is going to be my daughter's driver. The body is in WAY better shape than the '88. I do have new fenders for the '88 as well as a good header and grille.

 

The '88 is either going to be used for parts for the '86 and then scrapped, or depending on exactly what we use off of it, turned into a rock buggy. It would make a sweet rock buggy with no fenders and a bobbed flatbed on it.

 

The current plan with the '86 is:

Put tires on it so it's off the ground and I can get under it. Tires were picked up today.

Disassemble the steering column enough to replace the ignition cylinder with the new one that should arrive Friday.

Disconnect the fuel pump and pipe it to a bucket to drain the fuel out. The truck sat for at least 11 years.

Take spark plugs out, put Marvel Mystery Oil in the cylinders and let it sit for a day, then check compression on all cylinders.

The engine does have oil in it, but smells of gas. It turns over easily. It needs a new radiator. The transmission does go through all the gears and the clutch SEEMS to work.

If the engine needs anything more than a small tune-up, it's coming out and a different engine is going in. Still deciding between using a SBC (can't afford an LS and it's a first truck for a kid anyway so that would be dumb) or the 242 out of the '88, which I realize is just as much work as swapping in a different engine.

[Awesome]

Sorry about that last picture in the above post. I tried to remove it and it's still there.

 

Tonight my daughter and I removed the ignition lock cylinder and the driver's side door skin after I unjammed the door for the third time. In the process I noted a few things:

 

1: No tilt column. Oh well, not a huge deal because the seats don't adjust anyway. Wife may not want to drive it though.

2: The dash is remarkably complete. A previous owner installed a set of actual gauges in the ash tray location to compliment the idiot lights. Nice touch.

3: The upper bearing in the steering column wiggles a bit. Need to look up how to replace that.

4: The truck has no front driveshaft. Probably pulled by the previous owner to use on a project.

5: The brake pedal goes to the floor without much resistance. Going to have to address that.

6: The clutch seems to be working. 5th gear seems to be difficult to get into.

7: It has some kind of aftermarket steering wheel that is lacking a horn button. It looks like a boat steering wheel to be honest. The fit isn't great and the lack of a horn button means it won't pass inspection here in Texas. Need to either add a floor button for the horn or replace the steering wheel. I'll probably just go to the junkyard and get a wheel.

8: The door skins are cardboard?! They are shot. Needs new ones.

9: I guess it had door problems. The door hinges are welded to the body.

[Awesome]

Alrighty. Making progress. She's a runner, boys!

 

Cylinders #1 - 4 in order:

 

 

 

 

 

So compression is a little lower on #3 and on #4, but they are still great. I call that a win. It has oil pressure as well! I poured some gas in the intake and she started up and ran for a little bit. It will catch and cough some but won't stay running even with the pedal floored. So, next on the list: tune up kit, fuel filter, tires. If it still won't run after doing the fuel filter and the tune up kit then I need to check the fuel pump pressure.

 

This was this morning in the middle of replacing the ignition lock cylinder.

 

 

Side note; it's easy to get the lock plate OFF without a lock plate tool, but nearly impossible to get it back ON without one. So I bought the tool.

 

[eaglescout526]

Careful with the TBI. It doesn’t like gas being poured down the gullet like carbs can take. But otherwise that’s a healthy 2.5L. 

[Awesome]

Roger, thanks for the tip. I'm hoping it just needs the tuneup and filter and that will take care of the problem. Never messed with a TBI setup before.

[Awesome]

Messed with the truck some more today. Finished putting the tuneup kit on it. Still no start, but it runs great on ether. I removed the return line from the TBI (wasn't sure which line was which) and only got a trickle of fuel coming out of the throttle body when the key was turned. I also did not see any gas being squirted into the throttle body. So I'm pretty sure the pump is bad (it's pretty loud when it comes on anyway). So here's a picture of my daughter removing the fuel pump from the tank.

 

 

She's almost got it out. She's going to finish removing it, then she's going to take the known good pump from the '88 and swap it to the '86 and we should be up and running. If not then there's some other problem I'm not aware of.

 

Got some roller tires on it for temporary moving about. They'll make good burnout tires (LOL) when we've got the truck drivable.

 

 

You can see the cab corner cracks in that picture.

 

I figured out why the brakes don't work. Got a pretty good leak on the rear axle when I pump the brakes, and the front hoses are shot.

[Awesome]

Alright, we got the pump from the '88 swapped over. The '88 has an absolutely disgusting tank and the sender assembly is all rusted up, BUT, the rubber hose was good and so is the pump.

 

This is the unit from the '86.

 

 

I didn't take a picture of the '88 unit, but it's the same except for being covered in rust.

 

So, the '88 pump was far quieter once installed, pumped much more gas out when the ignition was turned, and had worked fine when we had the '88 running.

 

We still could not get the truck started. So I disconnected the pressure side line from the throttle body, turned the key, and got a really good squirt of fuel. Hooked it back up, truck ran on the gas it squirted into the intake but then quit. So either the injector or the pressure regulator is bad/dirty. I am going to look for a writeup on how to fix that, as I've never messed with a TBI system before.

[eaglescout526]

Check my signature for how we got to a bad injector. There is a DIY on rebuilding them. Feel free to shoot me a PM too as I believe I’m the resident 2.5L expert.(knock me off my high horse if I’m wrong guys)

[Awesome]

Wow, 25 pages of diagnostics in a week and a half. Very nice. I'm betting my injector is clogged. The fuel tank was empty except for traces of horribly old stale gas. I don't think I've really put enough gas in it to dilute the terrible stuff down much. I've got maybe 3 gallons in the tank.

 

Is the injector the part in the middle of the intake that has two wires on the top of it?

[eaglescout526]

11 minutes ago, Awesome said:

Is the injector the part in the middle of the intake that has two wires on the top of it?

Yes it is. Be very careful when you replace the injector after removal, you don’t want to snap the special screw….been there done that. 

[Awesome]

It RUUUUUUUUNNNNNSSSSS!

 

 

Pulled the injector, stuck it in the ultrasonic cleaner, cleaned off the remnants of the lower O-Ring, found a Viton o-ring that looked like it was about the right size, oiled it a little, slipped it in. Reinstalled. Cranked for a bit. Started up. Runs! I drove it around the yard and down the driveway a little bit. It has next to zero brakes, so that was fun. Transmission and clutch seem to work fine.

 

It sounds like it is idling a bit high (no tach  ) and has very little power, so I think there's vacuum leaks. Going to have to find those. Dad thinks I was in third gear accidentally, and I could have been. I was a little excited. The valve cover leaks oil, so that needs a new gasket.

 

Next on the list: dad ordered a new tank and sender/pump assembly today. That should be here later this week. Brake hoses come next though. I had bought a set for the '88 and never installed them, so I already have a new set laying around lol.

[eaglescout526]

Always good to see another 2.5L will see the road again instead of the 4.0L swap into soup cans.

[pizzaman09]

Sweet!  Getting a vehicle moving for the first time in a long time is always exciting.

[Awesome]

5 hours ago, eaglescout526 said:

Always good to see another 2.5L will see the road again instead of the 4.0L swap into soup cans.

 

Well we aren't done yet. After I fix some vacuum leaks and get the brakes working, I'm going to test drive it on the road to see if it will reach safe speeds for Texas roads. If it doesn't have the power to do 70mph then it's likely still going to need a different engine.

[GrandBoost98]

[Awesome]

Back at it again today. Cooled off some this afternoon with a nice wind blowing through.

 

Removed the rear brake hose and the front passenger brake hose and replaced them both. Could not get the rear upper brake line fitting loose even with vise grips, so I had to cut the hard line and re-flare it. The bottom two nuts and the front nut came loose with vise grips, so I didn't have to replace those fittings (yet).

 

Daughter worked on getting the gas tank removed. She has all the straps loose, and got very frustrated trying to loosen the hose clamps on the filler neck. She gave up after trying for a while. Hopefully tomorrow we can get those loose, get the new tank in and replace the last brake hose. Then I just need to put some fuel in it, bleed the brakes, and away we go.

[Pete M]

On 6/22/2023 at 10:32 PM, Awesome said:

Sorry about that last picture in the above post. I tried to remove it and it's still there.

 

 

gotta also tap the X in the box of that photo at the bottom where all the photos are piled up before you post.   

[Awesome]

After church today, I rested for a couple of hours and then we got to work.

 

Daughter removed fuel tank while I replaced the last brake hose. I ended up doing a lot of the tank removal work, as some of it was stuff she wasn't strong enough to do.

 

 

 

New tank in place.

 

 

The new no-name fuel pump assembly was different than the two I pulled out of the MJs. It fits, but has a bigger pump and wouldn't go in the tank without me bending the sender bracket. It came folded up in the box and I had to unbend the return line in order to get it back in shape. It doesn't go into a grommet in the tank. It came with a grommet on the return line, but doesn't line up with the hole in the back of the "pan" inside the tank where I think it's supposed to go.

 

Got the brakes bled as good as I can at home, then put five gallons in the new tank and started her up. She started right up... but I think she's running pretty rich. Smells like it, anyway. Think I figured out why the previous, previous owner dumped the truck... probably wouldn't pass smog.

 

Ran it down the driveway just to test the brakes. Tests fine. Engine seems to be running ok. I think my "low power" problem is that I'm not giving it enough gas when I engage the clutch. I have no brake lights or turn signals, so I didn't get to road test it. I'll do that in daylight when I can use hand signals. We got done about 9:30 PM.

 

Is that driveshaft stock for a longbed truck or did someone sleeve it? Really seems like overkill. It's as big as the shaft on my 3/4 ton truck.

[WranglerMangler]

My stock 2wd shaft and its backup is sleeved like that too. I’ve ran across other MJ shafts that are sleeved as well. Can’t say they all came like that but it seems like most stock ones are. Keep up the good work. Keep that girl wrenching too. I just had my 9yr old daughter out scrubbing rust off a flywheel for me. We’re pulling the transmission tomorrow. 

[Awesome]

Drove it down the road today.

 

The hazards decided to start working last night, confirming my suspicions of a bad contact somewhere. They flashed for half the night and drained the battery. I replaced the fuse and it was melted, but not blown. Probably from a bad wiring job. Lots of badly done added wiring under the dash. Wire nuts and the like.

Anyway, so all the lights work now. I charged the battery again and then this afternoon my daughter and I took it out.

 

 

It runs quite poorly. It stalled nearly every time I let off the gas, and wouldn't go above maybe 40mph (gauges aren't working). 3rd gear was all it'd do. It doesn't sound great, and smells worse. It had poor throttle response. 

 

I'm going to have my daughter start tearing the interior out while I figure out what I'm going to do about the drivetrain. I have no idea why the engine is running so poorly. It sounds like maybe it's missing, but then catches and revs up. I'm not sure what would cause that though.

 

It may be just as much work to get it running right as it would be to swap a different engine into it. No idea. I will need some help with the next part.

 

EDIT: A friend told me the cat may be clogged up. That would cause a lot of the symptoms I'm experiencing, so we're going to drop the exhaust and see if it clears anything up.

[eaglescout526]

33 minutes ago, Awesome said:

figure out what I'm going to do about the drivetrain

Oooo oooo pick me! Pick me! I’m willing to bet the TPS is out of whack and the vac lines needs some love. 

 

34 minutes ago, Awesome said:

but then catches and revs up.

ISA motor is doing its job by revving it up to stay alive. That part of the circuit is working. Is there coolant or water in the cooling system? A bad head gasket would also behave the same way as a clogged cat. 

[Awesome]

1 hour ago, eaglescout526 said:

Oooo oooo pick me! Pick me! I’m willing to bet the TPS is out of whack and the vac lines needs some love. 

 

ISA motor is doing its job by revving it up to stay alive. That part of the circuit is working. Is there coolant or water in the cooling system? A bad head gasket would also behave the same way as a clogged cat. 

 

I think I saw a TPS adjustment writeup here on the forum last week. I'll have to find it again. I also still haven't blown propane around to try and find vacuum leaks, so I'd better get on with that. I should explain better: when I step on the gas it doesn't really do much until I give it about half throttle, then it lugs a bit and then suddenly revs up. Once it's running at higher RPM the engine sounds pretty smooth.

 

It has coolant and it's green. Old, but still green. The oil isn't foamy and looks pretty normal. It does blow smoke though so I suppose it's possible it has a bad head gasket. Compression checked out fine though.

[eaglescout526]

Lets do the easy stuff before tearing into the head.

[Awesome]

I'll get on that tomorrow when I remove the cat and start checking for vacuum leaks. Probably won't get into the TPS before I call it quits for Independence Day.

[Pete M]

23 hours ago, Awesome said:

 

 

 

raisin' 'em right.