Check engine came on and scanner read cylinder 1 & 2 misfired with a small emission system leak detected. Replaced the fuel injectors and it the light came back on couple days later. Scanner read cylinder 2 misfired and replaced fuel injectors with better ones including coil. Check engine light came on again today, around 3 days later. I’m just trying to see if anyone else has had this problem before, might not give enough information but the jeep was a gift from my dad whose the one that has taken it to the shop both times. Not sure what it could be. Runs perfectly fine but can chug from time to time. I love it and wish I knew how to work on it myself! Any tips for beginners would be appreciated

 

What year do you have ? and have you checked compression yet ?

 

it’s a 2001! And I have not, is that something I can do myself?

 

A 2001 that's the same year I have , does yours have the OEM 0331 head still because they like to crack . Have You been losing coolant ? It doesn't need to be alot of coolant and check the oil because thats where the coolant goes most of the time . and yes you can do a compression test your self .

 

I’ll check on these things tomorrow and get back with you! Thank you so much!

 

Sounds like the drivability is not significantly impaired since you say it runs otherwise fine.
Injectors are just one cause for misfires, the spark ( or better said lack of) is another example.But not the only ones..

Do you notice the misfires and when( or is that what you mean with the occasional chug?). While driving, or when idle?

 

Have you pulled the spark plugs to take a look? My 2001 started to misfire without any warning with vibration (chugging) and loss of power. Code was a P0304 (cylinder 4 misfire). Pulled the plug to take a look and it was fouled. Cleaned plug and swapped the #4 with the #3 plug (which looked normal). Running good now but will check plugs again in a while to see if #4 dirties up again.

 

**What is the current state of existing codes with your XJ? Same cylinder, cylinders? Emission leak code still there too? Post all current codes you now have.

**With a "new to you" XJ, it's time for new spark plugs. Easy stuff first.. always. You don't want to be chasing your tail for something simple like plugs. I like the NGK brand spark plug for your 2001. Be sure they are gapped properly to .035 before installing. After that, if you are still experiencing a misfire, I would run the compression test that others mentioned. The spec for the 4.0 engine is 120-150 psi with no more than a 30 psi variation between cylinders. If you don't have the tester, they can often be rented very inexpensively at many parts stores; call around for availability.

**Along with compression, need to be sure that the fuel injector for any cylinder that is misfiring is actually firing. This can be done with a simple "noid light" which can be purchased at most any parts stores.

**The emission leak code is not likely related to your misfire, you have two different things happening. Post the EXACT code for the emission leak, with OBD codes...the devil is definitely in the details! Sometimes it is as simple as a faulty gas cap but often it is more complex and diagnostic testing needs to be done to determine root cause. There is something called a smoke test which is often used to figure out emission leaks like you are experiencing. Any shop can perform this for you.

Note....if the check engine light is FLASHING, that indicates a serious misfire which if ignored, will destroy your catlytic converter in a short period of time as misfires cause raw fuel to be dumped into the cat and it can't process it properly....so this problem must be resolved immediately or you'll have bigger fish to fry.

Good luck and keep us updated!