My engine started misfiring awhile ago and i havent been able to fix it. It only misfires when moving not when its idling. I changed the ignition coil and spark plugs.
Misfire
- Thread starter MuffinMan1234
- Start date
Rubicon88
TJ Addict
Bosch plugs don't have a good history in our Jeep engines, they are known for not running well. A Bosch engineer opined years ago on this issue saying he believes its the limited heat ranges Bosch has available when compared to more mainstream spark plug manufactures like Autolite, Champion, and NGK.
I'd first try swapping to a more mainstream spark plug. Your 2.5L engine isn't fussy, a basic plug like the Champion 3034 or Autolite AP985 would work well. Both of those are platinum tipped and would work well for something like 100k miles. Autolite's XP-985 is iridium tipped and it'd likely be fine for over 200k miles. NGK would work fine too. One member here thinks our Jeep engines were designed to only run well on NGK but that's simply not true. I've been running Autolite's plugs for 25+ years without issue though it's not the only plug brand that is suitable.
Then check your distributor cap and rotor, they could be worn. If they're suspect, replace them and if you can find them with brass contacts, go with that. They last longer than cheap distributor cap/rotor sets with aluminum contacts.
If that doesn't help I'd suspect you have a bad crankshaft position sensor. Mounted to the transmission, it's what provides the master timing signal to the computer. This is the one I'd go for for your '97 2.5L with 5-speed. The CPS does vary by transmission type so be wary. https://www.amazon.com/dp/B006EFUF2I/?tag=wranglerorg-20
Make sure not to install any store brand crankshaft position sensor if you get to that point. Store brand sensors are notorious for having poor quality or short lives if they do work properly at first.
A basic Tune-up is a good place to start. We tend to focus alot on spark plugs,
but Dist. cap , Rotor , and Good ignition wires
are all part of a good reliable ignition system.
Replace them with good parts to establish a solid baseline to judge from.
The parts are not that expensive.
Rubicon88
TJ Addict
If you came here or a genuine Jeep store unless the problem immediately jumps out at the person diagnosing the first thing is getting the problem area to ground zero.
Ground zero would be a simple plug change to what the MFG recommends.
The MFG recommends the NGK ZFR5N. It's close to the cheapest applicable Jeep plug as well so that's a benefit.
Knowing Jeep specifically recommends this plug will give you confidence the spark plugs are eliminated as a possible problem.
That's the whole goal here...no? Rid the problem.
Other plugs might work but the ZFR5N will work.
If someone is chiming in to help rid a problem I'm not sure why they wouldn't want them to get to ground zero and proceed with a diagnosis in lieu of some personal love affair with a specific product.
Oh well
Ground zero would be a simple plug change to what the MFG recommends.
The MFG recommends the NGK ZFR5N. It's close to the cheapest applicable Jeep plug as well so that's a benefit.
Knowing Jeep specifically recommends this plug will give you confidence the spark plugs are eliminated as a possible problem.
That's the whole goal here...no? Rid the problem.
Other plugs might work but the ZFR5N will work.
If someone is chiming in to help rid a problem I'm not sure why they wouldn't want them to get to ground zero and proceed with a diagnosis in lieu of some personal love affair with a specific product.
Oh well
Well, I am glad we can get back to the original OP's misfire issue. 
MuffinMan, let us know what you find / replace and if it solves the misfire issue !
Hang in there, this can be solved !
MuffinMan, let us know what you find / replace and if it solves the misfire issue !
Hang in there, this can be solved !
Jerry mentioned the crank position sensor. That was the culprit when my old '97 had a misfire.
I didn't even have to replace it. I just cleaned off the gunk that had accumulated from an oil leak I had been neglecting.
I didn't even have to replace it. I just cleaned off the gunk that had accumulated from an oil leak I had been neglecting.
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