The Check engine light on my 98 xj 4.0L keeps coming on. When they clear it they tell me is a cylinder 1 misfire. I have changed sparkplug, wires and thru in another injector. It deffinetly sounds like it is missing during idle. And thats when the light will come on. No one around me has an engine scope so i can see whats going on. I know it could be a lot of diffrent things but what route do you think i should take next.
Not sure if you need to know this but my gas mileage has takin a dive and when the engine is cold, it sounds like there is an exhaust leak.
Thanks for the help

 

did you clean up on the contacts on the cap and rotor when you put new wires on it? maybe those are corroded?

 

Actually i did not do that, I will try that as soon as i can.
thanks for the idea, Would you suggest a wire brush, sand paper, what about any kind of dielectric grease?

 

You could do a compression check and see if you have a burned valve

 

Is this simething that i can do at home. Like rent a guage and check it?

 

Yes.

 

ok i will look into that and then give an update, it might take me a couple days, kids take up a lot of time

 

I removed and cleaned the distibuter cap last night, it sounded like it was idleing the same. Won't know about the check engine light for a day or two. When it pops, its usually 2 days after i reset it. Making me think for two days that i fixed it.
I will do a compression check next. Does anyone know what pressure i am looking for?
Thanks

 

125-150 IIRC, you need to check all cylinders, they should be within 10% of each other.

 

You can get a compression tester from AutoZone type stores for a deposit that's returned to you after use, btw.

 

Awesome thanks,
It didn't pop today but i will still do a compression check asap

 

So its not from the distributer cap being a little dirty. It popped again on the way to work, this time i was going about 35 on and off gas due to traffic when it popped. Starting to get a little frustrating bc all i can see from here is dollar signs. Will update about a compression check asap

 

If I were you, before running a compression test, I'd replace the dist. cap and rotor (really should be done anytime you tune up). I highly doubt its a compression problem.

 

exhaust leak, you say? that will definitely foul a spark plug. i am willing to bet that is the root of the problem - exhaust leak is causing cylinder 1 to run too lean (especially if the leak is close to that cylinder). try this old harley trick - add a teaspoonful of oil through each spark plug hole and run it. it will smoke profusely for several minutes while the oil is being burned off and this smoke will find it's way out of anywhere it is leaking.

 

I could see how that would work and might deffinetly try that.

Now, this is interesting and remember the light does not come on all the time. every two days or so, only when the engine is hot and it never resets itself.

i went to take the jeep to the auto hobby shop on base while the light was still on to make sure it was still a cylinder 1 misfire since i just got done messing with the distributer. Maybe it moved to another cylinder meaning somethings up with the cap and rotor. parked at the shop to go in and get a stall, came back out started the jeep, it was a wierd start (can't explain). Anyway, after it started, the dang light went out, Its never just went out. We hooked up to the obd2 and said everything passed. i figured it would atleast kept the code in the brain for a couple minutes, nothing. At that point i wasn't to happy bc i needed to know why the engine light had popped, is it still cylinder 1? Well after hovering over the engine while i noticed the wiring harness that holds the wires to the throttle position sensor,IAC, Injectors and the other sensors laying on top of the extremly hot intake manifold. Where it is making contact, there is no protective covering on some of the wires. Not sure if that is causing a problem but it might have an affect.

Now messing with the TPS, i have noticed that it is making the throttle stick. Normal idle is 750 and it sticks around 1300-1500. The only thing that resets it is killing the motor and starting it up again. I don't like electrical problems. I think i am going to replace the tps and see if that fixes the problem. These two issues,(misfire and throttle sticking) might not have anything to do with each other.

I have also read about vacuum leaks, i have been told to take carb cleaner and spray all around cylinder 1 and the rest of the cylinders one at a time to see if the rpms increase. If it does i have a vacuum leak.

Sorry for the long post but had to throw everything out there,
Thanks for reading