Hello, I'm new to the forum and new to jeeps. Was looking to purchase a really nice 2000 xj, the owner has been very honest with me and i'm just looking for answers to a disclosed problem with the jeep. The problem with the jeep is that the CEL comes on and throws codes P0300(misfire)P0303( cylinder 3 misfire) and P0304 (cylinder 4 misfire). it does not shut off but gets sluggish. this could happen when pulling out of driveway or after 40 miles, there is no real pattern. Sometimes shutting it off and clearing the codes fixes it, sometimes not. Seems like the computer is shutting down injectors 3 & 4.there has been compression tests done,heat soak, and also synchronizing the cam sensor, all were fine. since this started happening he has replaced the following-crank sensor, cam sensor, coil packs, plugs, fuel injectors, injection rail, flex plate, ecm, and engine wiring harness. he is thinking that the problem is electrical because of it having no pattern. he is just out of patients and is done throwing money at it! im just trying to find out what it might possibly be that he hasn't! already done, so i can be the jeep and enjoy it! Thanks in advance for any suggestions

Easy one for me. Look at the feed harness for the coil pack. There's probably a chaffed wire for coil #2.

The harness I'm talking about connects to the coil rail and has 4 wires in it. One is power and the other 3 are grounds that connect to the PCM. I was originally going to tell you to replace the coil rail, but he's already done that. The coils are known to short internally and seeing as how both 3 and 4 fire together, I suspect a fault with that coil. If the coil rail is new, that only leads to the wiring. This, of course, is only my opinion but I've had the rail short on my WJ already. The PCM fires the coils by opening the ground circuit for each one, thus allowing the magnetic field to collapse creating the spark. If that wire is intermittently grounded, it won't create a spark OR if it's NOT grounded, it can't build a magnetic field either. Now it's possible the driver in the PCM is intermittent, but you'd have to back-probe the proper wire in the harness connector to know for sure. It seems the PCM has already been replaced as well.

The bottom line is he honestly tried to fix it, but it's going to take an electrician to find the problem. As long as the compression is good I'm pretty sure there's nothing major wrong with it. The fuel injectors are powered up all the time the engine is running and the PCM GROUNDS them in sequence only when fuel is needed for that cylinder. It's hard for me to believe just 3 and 4 are effected.

Wow - talk about "firing the parts cannon"!!!

I have to agree with GreaseMonkey. I'm not a professional mechanic, but merely working the parts counter at the local parts retailer for a couple years in college I've seen plenty of that.
The best way to know for sure is to see documentation - receipts for parts and service.

I also think Dave is onto something and my gut feeling is that the seller is a well intention-ed guy.

If it were me, I'd see if I could take the Jeep for some amount of time with freedom to dig into it and at least see if it is just a chafed wire. Maybe see if you can dig into it at his location for a few hours if nothing else.
IIRC that coil pack wiring is kind of a pain in the rear to get at.

If the engine is in good condition and the body is in good shape (rust being the main concern) and you can get the Jeep for a good price, it may be worth it. The good thing is that you likely would be able to sell it for about the same as you paid for it if you changed your mind.

You might check around for a local automotive electrical expert or Jeep specialty shop that is willing to go through the wiring and find and replace anything that's not in good shape.

The other thing to be aware of with a 00 is the 0331 head defect - do some research on this if you're unaware. It's not related to the issues with the codes, but if you own a 00 Jeep you need to be aware of it.

Pathenry, thanks for advice

Anytime brother!

If you do decide to get the Jeep, this forum has a ton of awesome folks that regularly visit and have a ton of great advice. Dave, as you can see is super knowledgeable, there's a guy Jordan96xj who is really great with electrical stuff and Cruiser54 who was a head Jeep mechanic. Plus a ton of pro mechanics and Jeep experts.

I had a Toyota question and dealing with the Toyota forums made me greatful for this one - I had one answer to my question. Here you'll get multiple responses and folks willing to walk you through a diagnosis. Aside from having a Jeep mechanic at your side, you won't find better help.

That is great! Going to take another look at jeep tonight, hopefully i can get it and solve this problem