I am a high school student that has a 2001 XJ. This jeep has ran great ever since we got it a couple years ago. When it would get hot it would throw the cylinder 3 misfire code. I went to the fuel rail and insulated all the injectors and the fuel rail, and I replaced the coil rail thinking it could be faulty as well.

This is where the issues start. I crank the jeep up and it is running good. I drive it to the auto parts store to pick up something and shut the jeep off thinking I have solved the misfire issue. I come out of the store the jeep cranks and is idling good. I go to back out of the space and the jeep dies when i gave it gas. It does this multiple times, but it will stay running if i keep the rpm's high. I drive home and the thing is running like garbage. It is running on what seemed to be 3 cylinders and it is popping. It sounds like what a lean pop would do if it had a carburetor so I replaced the injector seals.

Now the jeep will start but it wont run. I went around and replaced:
-Crankshaft Position Sensor (Mopar)
-Cam Position Sensor cap
-Coil Rail Plug Connector

After all this is replaced we started thinking it was the ECM so I went to a junkyard to get one; it doesn't run any better so, I put the old one back in it does the same thing. Then it wont even crank up. I ordered a new ECM and it will start but it won't run.

I went through the wiring harness to see if there were any broken wires, and there weren't. The jeep will fire up now run really bad then shut off. It will give these codes.
-Ignition Coil 1
-Ignition Coil 2
-Ignition Coil 3

I have no idea what to do next.

 

Check for power at the coils.

 

Its getting power at the coils because it fires up on six cylinders. Then when it goes to idle it runs on four cylinders for a little bit.

 

Did you have your battery tested? I've owned two XJs and when the batteries were failing, I had weird symptoms just as you describe. The XJ computers don't like bad batteries. Can't hurt to have the battery and charging system tested at a local parts store. It's free and takes only a few minutes.

 

The charging system is fine because it was running well before. The battery might be a little low because of all the cranking it has done.

 

Have the battery tested. It could have one or more bad cells which would cause the symptoms you describe.