Whats with this my baby

[cnpower]

This is my first post, hope you guys can help me out.

I have a 99 classic that I bought used and been running good till about six months ago. It gradualy started getting rougher at idle, and not when its cold but when warmed up. The scanner gave me a code P0304, missfire #4. The #4 plug was fouled out. I replaced the cap, rotor, wires, plugs, #4 injector and this helped for a little while. Now doing the same thing, same code, and now it misses bad on accelertion and on down shift when pulling a hill.

I have unplugged every connection that I see and cleaned them with contact cleaner.

Please Help

[fredjacksonsan]

cnpower, welcome to AF. Hopefully you will stay awhile like lots of us have.

It might be the Crankshaft Position Sensor (cps). There are many issues with that sensor, and it usually starts giving up around 90 or 100k miles. You didn't say if you have the 4.0 liter six or how many miles, but based on your description I bet you do, and that it's around 100k.

Let us know.

[Ros981500]

I had the same problem with mine last year. Replace the crank case sensor ran fine for a little while two days. then found distributer was worn. Replaced and that fixed it..

[cnpower]

Thanks for the feedback...I will get back to later in the day

[Saudade]

There is also a known vapor lock issue with the #3 and #4 injectors. It usually shows up during a hot start, but could also be part of your problem. There is a service bulletin on it. If you search the forum, you should easily find it (or even use Google).

[cnpower]

Originally Posted by fredjacksonsan

cnpower, welcome to AF. Hopefully you will stay awhile like lots of us have.

It might be the Crankshaft Position Sensor (cps). There are many issues with that sensor, and it usually starts giving up around 90 or 100k miles. You didn't say if you have the 4.0 liter six or how many miles, but based on your description I bet you do, and that it's around 100k.

Let us know.

My rig 143000 mi on it, I changed the cps, still runs the same

[ctwright]

Originally Posted by cnpower

My rig 143000 mi on it, I changed the cps, still runs the same

You might still have to take your spark plug out too though and clean it again or put a new plug in.

[ctwright]

Just my opinion but I think the the crank going bad would have caused a multiple misfire problem instead of the problem with only your #4 cylinder.

[ctwright]

I would replace the coil pack that has the wire going to that plug and see if you notice any difference.

[ctwright]

Never mind I just seen where you said you replaced your cap & rotor button so you don't have coil packs. After everything you've already said you have done I would pull the head and take a look at the valves.

[cnpower]

Well the main problem with my 99 cherokee was carbon build up in the Idle Speed Motor port and and Im shure the valves, also a crack in the ceramic #4 spark plug.....a rooky mistake by me...

Thank You all for your input!!