200,000+ miles on the jeep. Has mis fire on one code active. I have changed ignition pack and spark plugs with tps. Still has active code also it won't start right away. Second or maybe third attempt it will start and run good. The fuel line and alternator has also been changed. Prior to me owning her. Need help first time jeep owner super excited. I don't wanna give up on her just yet.

 

If you have to dive in blind, then here is how I would start.

1. Take 20 minutes and cleanup up all of your electrical connections (battery terminals, clamps, ground connections).

2. Take a moment to test that your battery is in sufficient condition to start the vehicle (should be in the 12.5v+ range). If it is lower than that, then try starting the vehicle by jump starting with another vehicle or known-good jump starter pack of some sort.

3. Verify Fuel Pressure, Air supply, and Spark, and Compression. (google these to ensure that you are testing them properly, so that you can truly rule them out).

 

Some things to try for your XJ.......

1. Swap the fuel injector from the code cylinder to another. See if the misfire follows with the swap.

2. Run a compression test on all cylinders. Share the readings with us for comment. The compression spec. for the 4.0 is 120-150 psi, with no more than a 30 psi variation between cylinders. With 200K plus on the engine, you can't eliminate the possibility of an internal issue without at least doing some basic testing and compression test is first up.

3. I agree with verifying fuel pressure. Very simple test to do on your "process of elimination" list. Many parts stores will rent you a fuel pressure gauge and a compression tester. For an 01, your fuel pressure spec. is 49 psi, plus or minus 5 psi.

Good luck and keep us updated!

 

Is it safe to assume the ecm was reset after changing parts and code came back? Also what misfire code? Was it random p0300 or cylinder specific? P0301 for cylinder one for example. The last number pertaining to cylinder number.

 

I will have to try these suggestions s thank you! The ecm was not reset. I'm not sure how to do that.

 

It was a specific misfire code p0301 or something to that effect.

 

by not starting you mean it cranks and doesnt fire on the first attempt? does it noticeably misfire when it is running?

have you checked to see if fuel pressure is bleeding off prior to starting? try cycling the key on/off twice before you start it. give the fuel pump enough time to prime the system (you can hear it) between cycles.