88 YJ Need help

[kiljoy]

I have an 88 YJ 4 cyl. 2.5. It runs but has rough idle. I've changed spark plugs, cap and rotor. Wires seemed brand new. Engine still has rough idle. With the vehicle running I pulled the spark plug wires out 1 by 1 and noticed that the engine's idle didn't change at the number 3 cylinder. I'm still getting adequate spark from wires. Also all but 1 of the spark plugs seems to be gunked up with black residue way too quickly. Any suggestions?
By the way I'm new to owning a Jeep so please feel free to insult my intelligence. Thanks for all the support.

 

[SteelHeadz]

Welcome to Jeepz. We are not here to insult anyone, we just like to offer suggestions, comments and share our knowledge.
I would suggest a compression test on the cylinders in your case. That black carbon or gunk could be caused by oil burning in the combustion chamber and fouling up the plug. The possible causes for that would be a worn oil and compression piston rings, gouged cylinder wall, or a leaking valve stem seal. Try replacing that 1 spark plug and see if the misfire condition goes away even for a little while. If so, you have verified the reason for the misfire(fouled plug), now just figure out the cause for the misfire.

BTW, don't forget to introduce yourself in our "New Members Introduction" section.

 

[Team Twisted Off Road]

I have an 88 YJ 4 cyl. 2.5. It runs but has rough idle. I've changed spark plugs, cap and rotor. Wires seemed brand new. Engine still has rough idle. With the vehicle running I pulled the spark plug wires out 1 by 1 and noticed that the engine's idle didn't change at the number 3 cylinder. I'm still getting adequate spark from wires. Also all but 1 of the spark plugs seems to be gunked up with black residue way too quickly. Any suggestions?
By the way I'm new to owning a Jeep so please feel free to insult my intelligence. Thanks for all the support.

You sead the plug wires seemed good but one may be bad... My jeep ran fine but when it rained it would not start come to find out it was the coil wire it was bad on the inside... so do the testing as steelheadz sead but also take a good look at the wires swap one out with a nother and see if the problem moves.. And :welcome: to JEEPZ

 

[yo momma yj]

check the compression and post the results.
diagnosis is simply ruling out what's good.

 

[54cj3b]

try checking your timming

 

[jfrabat]

try checking your timming

As far as I know, the 88 is the same as the '94 in that the ECU controls the timing, and there is no way to adjust it...

I agree with Steelz's suggestion, by the way.

 

[kiljoy]

I finally got the chance to do a compression check on the engine and here's what I found out. According to the Haynes manual I should have between 155 to 180 psi. I have a consistent 150 psi on all 4 cylinders. I'm not sure if 5 psi would make all that much of a difference or not. If it does make a difference, how do I correct the problem?
If it doesn't make a difference, what's the problem? Help is greatly appreciated.

 

[elevatorman]

usually if your compression readings are within 10 percent of one another you are still ok- 5 PSI off should not be a reason for concern.
I agree with all the advice. The cheapest is to swap that bad wire with one of the others you know is firing and again see if the problem moves to the other cylinder