Anyone know how to fix spark knock. I'm working all the bugs out of my rig and this is one. It's a 98 xj.

 

Which engine?

 

It's a 4.0L

 

Start with cleaning out the combustion chambers using Chrysler Combustion Chamber Cleaner (get from dealer), then replace the spark plugs. Your year calls for Champion RC12LYC plugs but you can use Champion RC12ECC or NGK ZFR5N plugs. Plug gaps .035" dead nuts.

Edit: Use a spark plug gap checker like this one. not the coin type or feeler gauges.

Won't hurt to change the distributor cap and rotor, and plug wires while you're at it. Recommend premium parts from NAPA for these.

Edit: Cap and rotor= Echlin, plug wires= Beldon.

 

Just changing the plugs made a drastic difference. I have never seen a set of plugs so bad. The gap was huge. I set them to .35 and the xj is running great. Thanks for all the help..

 

The spark plug gap checker you linked, goes from .040 to .080. No good when you need .035. Try one......RR

 

Basic maintenance works once again!!

Dave, if the plugs were that bad, I'm betting the cap, rotor, and wires are also. Replace them with quality parts as Ken suggested. Clean your throttle body while you're at it.

Just wondering. Have you ever checked the lube level and condition on the transfer case and diffs?

 

Thanks for the heads up. I didn't notice the other one didn't have .035.

I have a Companion 9-4075 wire spark plug gap gauge tool that I bought at Sears many years ago. You can't find them anymore but I see on the Sears Tools website that KD Tools makes it now. These are the best you can use.

http://www.sears.com/kd-tools-spark-...5&blockType=G5

 

I'm going to be doing the wires and such here soon. I have checked my fluids and topped them off for now but with me working for valvoline instant oil change I'm just waiting to get my discount to Do my manual trans both diffs and my t-case all at once.

 

Good plan.