86'Cj-7 I'm stumped

86'Cj-7 I'm stumped

jeepjunkie

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farmington ct
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86' Jeep CJ-7
I'm suffering from a total loss of power under load or up a hill at about 35mph. Here is a list of things I have replaced or removed. I have well over 2k invested in trying to chase this gremlin down and no luck. My mechanic threw his hands in the air and gave up. Now I'm stuck.

Ignition coil (new)
carbeurator (new)
fuel tank and sending unit(new)
fuel lines (new)
fuel filter (new)_
wire, plugs, distributor, rotor(new)
catalytic converter(removed)
ignition module(new)
brakes and lines(new)
water pump and thermostat(new)
fuel pump(new)


If I've forgotten it, it's probably new. Now here is the million dollar question. I did a compression test and cylinders 1-5 read 110. Cyliner 6 read 100. Based on my readings, the 4.2 liter should be reading between 140 and 160.
Is my engine shot?

My friend offered me his whole truck which is a 98 cherokee with 180k on it and it purrs like a kitten for 500.00

1) is this a compatible swap?
2) does is sound like my engine is toast?
2) I have a straight 6 out of another 85 cj that I have, should I just swap these out?


Thanks in advance!!
 
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It sounds like the motors weak.
Leaking at rings, valves or some combination of the two.
How's the compression on you 85'?
 
Not tryin' to piss you off, but after replacing all those things, I would want to go back to basics, check grounds, vac. lines, and the like- your compression #'s ain't great, but not terrible either, I've seen worse, and it could be something simple- try, try,try, then jump off the cliff-

Bush
 
I've done that over and over, vacuum lines are all set, vacuum advance is working, timing is perfect, I brought it to my friends house where it sits who is a triple master mechanic. He threw his arms up and said he's out of ideas. We lifted the rear end and got to thing to over 80mph on the speedometer with no problem. Any kind of load it just dies out. I'm ready to jump off a cliff. I'm acutally praying that it is the engine so I can just do the swap. I thought it might be vapor lock and insulated all the fuel lines and that wasn't it either.

What grounds do you thing would cause a power loss? Ignition coil? I'm willing to go back for sure but I'm just not sure what to recheck that I've already rechecked.

Thanks for the insight, greatly appreciated.
 
Either you engine is tired (the spec is lowest cylinder needs to be at least 80% of highest), or your carb is bad. Just because your carb is new, doesn't mean it is good.
 
The 98 Cherokee engine swap would be great!. You would want to swap the fuel pump, wiring and computer as well. You would end up with a good smooth running fuel injected beast!


On your current engine, what's your total ignition timing set to???

If it sound like it's running and revving out smooth but falls on its face under load, it sounds like it doesn't have enough advance. Are you sure your mechanical advance it working? When you rev it up, it should have at least 32 degrees of total advance, or probably more depending on your elevation, jetting, compression etc....

Does it actually die, or does it just have an incredible lack of power?

One less likely scenario that is still possible is that maybe your timing chain skipped a tooth? If your cam is retarded one tooth, it would definitely make your engine gutless!
 
csuengr; I replaced the carb twice thinking it was bad the first time. All vaccum lines are working and the vacuum advance is working. When it idles there is a small skip that has never been tracked down. Timing is dead on if I remember correctly it's supposed to be at zero not sure but whatever its supposed to be it at. I'm thinking I might do the engine swap with the 98 Cherokee ,It's got a 180k but has been babied and runs like a top. Wondering if anyone has had any experience with these specific engine swaps? Any input appreciated.

Thanks,
Rick
 
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The timing should be at 12-15 degrees BTDC at idle.
 
The timing should be at 12-15 degrees BTDC at idle.
The timing at idle might be right on, but if his mechanical advance isn't moving it up to at least 32 degrees by mid to high RPMs, it'll have no torque under load.
 
csuengr; I replaced the carb twice thinking it was bad the first time. All vaccum lines are working and the vacuum advance is working. When it idles there is a small skip that has never been tracked down. Timing is dead on if I remember correctly it's supposed to be at zero not sure but whatever its supposed to be it at. I'm thinking I might do the engine swap with the 98 Cherokee ,It's got a 180k but has been babied and runs like a top. Wondering if anyone has had any experience with these specific engine swaps? Any input appreciated.

Thanks,
Rick

Get hold of a dial back to zero timing light, rev the engine and see how much timing you have when not at idle. If for some reason your mechanical advance is stuck and not giving it a whole lot more advance when revved, it would make it have no power under load, even though it revs smoothly when the wheels are off the ground.

You'll find lots of guys on here that have installed a 4.0 head and fuel injection from a later model cherokee, but not as many that have swapped the entire 4.0 into their CJ. It's basically the same thing though, because you'll need to swap the computer, wiring, and fuel pump assembly over to make it work.

Everyone that's done the fuel injection and computer swap seems to really like it.

The only real difference between your 258 bottom end and a 4.0 is that the 4.0 has a bigger bore and a shorter stroke.

Just look up threads on doing the FI swap and they'll tell you everything you need to know to do the whole engine swap. The good news with the whole engine swap is you won't have to figure out how to mount the crank sensor since the 4.0 already has it mounted. :)
 
what carb do you have exactly? is the factory carter bbd, or have you swapped something else onto it? if it is the factory carter you gotta remember that it was junk when new, now 25 years later its really junk, even though you are buying remans (because they don't make em new anymore) they can still be garbage. also with the factory carb that means you most likely have the factory computer connected along with all of that junk and there is no telling what is bad in that birds nest of :dung:. i say before you go swapping motors around, try giving a motorcraft carb a try it might just solve all of your problems, and itll be a hell of alot easier/cheaper to swap than the motor. plus if it doesn't help you can always use it on the next engine that finds its way in there. i also agree with rescue, id pull the timing cover and check the timing chain, to make sure the thing is still in time.
 
i also agree with rescue, id pull the timing cover and check the timing chain, to make sure the thing is still in time.

With the right tool, he can check the valve timing by just pulling the valve cover. That would be a whole lot easier. :)
 
Diver thanks for the info really helpful, I'll check it out. Sorry for the ingnorace but where is the mechanical advance located so I can check it out and replace it if it's not working?

Thanks
 
Diver thanks for the info really helpful, I'll check it out. Sorry for the ingnorace but where is the mechanical advance located so I can check it out and replace it if it's not working?

Thanks
Mechanical ignition timing advance is a couple of spring loaded weights located in your distributor. When the distributor shaft rotates, the weights ae pushed out by centrifigul force which rotates the plate in the distributor that holds the ignition module which advanced the ignition timing as the RPMs increase.

Don't confuse ignition timing with valve timing. Valve timing is the rotation of the cam shaft in comparison to the crank shaft. That could be off if your engine has a whole lot of miles on it, and the timing chain is so stretched that it alowed it to skip a tooth.
 

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