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Discussion Starter · #1 ·
Hi all, new to this forum, and looking for some help. The 6 cyl in the 87 Wrangler I just bought has an issue. New carb, new dist. new plugs and wires. The engine has for a better word, cough at about 3000 rpm under power, it hesitates then takes off again. Tried adjusting timing but does'nt seem to help. Anybody have ideas. Thanks
 

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An 87 Wrangler has the 4.2L motor in it. And although it should be smooth throughout the entire RPM range. at 3000 you are above the operating range. The 4.2L max is around 2600.

It is designed as a low end RPM torque motor. It isn't designed to be run in the higher RPM range, like the 4.0L is. Although it can climb into the higher rpm's, it is just basically a waste of gas. There is no performance gains from running it that hard.

To get back to your reason for the cough. Although it is possible it could be 1 of the stepper motors on the junky stock carb, it is most likely valve train lash, or for a better word, slop in the timing chain. Unless the chain and gears are fairly new, the tensioner gets wore and allows the chain to slop back and forth. The chain runs from a gear on the crankshaft to a gear on the front of the cam shaft. The cam moves push rods that open and close the valves. Your cough comes from the cam not catching up with the rest of the motor due to too high of rpm's.

Stay under 2600, and the motor will perform fine.
 

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Discussion Starter · #3 ·
Thanks, for the idea. Is there any way to adjust the tensioner on the timing chain? I'm sure i was off on the RPMs I'll check that when i go home today. thanks again.
 

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No, there isn't an adjustment on the tensioner. It is just basically a piece of spring steel with a plastic piece molded to it that rides on the timing chain and keeps the "slop" out of the equation.

It requires tearing down the entire front of the motor to get to. Although it isn't a hard process, it is time consuming. By the time you take the belt off and the fan and the water pump, and then the timing cover, then replacing the tensioner, and possibly the timing chain and gears if they are worn too bad. Plan on spending the better part of a weekend working on it.

A good mechanic can do it in a few hours, most backyard mechanics (if they have all the proper tools) it will take at least twice that long or longer.
 

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is there anything that can be done to get more top end out of my 4.2. just bought it a couple months ago and on the highway 60-65 seems to be top end. I can go 70 but 3k to 3200 rpms it's really working hard.
 

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need more info such as lift tire size auto or stick what gear ratio are your difs.. it all plays a role into it.. your driving a brick into the wind not really aerodynamic
 

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need more info such as lift tire size auto or stick what gear ratio are your difs.. it all plays a role into it.. your driving a brick into the wind not really aerodynamic
This. If this doesn't apply you might have a clogged cat. When that happens it runs fine there's just no top end.
 
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