So my 2000 xj 4.0 once up to temperature starts skipping and running really rough between 2200 and 3000 rpm. The jeep will idle rough and is skipping. I ran it in the garage tonight up to temperature and than for another 5 minutes or so. At this time I couldn't get the check engine light to come back on.
When The check engine light comes on than it will flash the longer you run it. I imagine when it misfires it makes the 02 sensors and everything else compound the problem.

Plan on having a second set if eyes/ears come by and run it up to temp and see if can get the CEL to come on.
If the jeep cools down and you start it later it will run fine again until brought up to temperature. I recently replaced the plugs and inspected the ignition coil; the plugs I pulled had about 10k on them and were not fouled not could I find any damage in cool.

Facts you should know:
110k
Recently did water pump due to leak 2 weeks ago. Small exhaust leak before the muffler. Heater core is clogged - has not had heat for awhile.

Head gasket done 1 1/2 years ago. 10k Machined the head.
Coolant system replaced entirely at this time (only exception heater core...kick myself...)

Thanks for reading

 

Forget more eyes and ears, you will chase this problem forever until you scan the codes.

 

Let it run for 5 minutes choking and sputtering bringing idle up to 2400 and no codes. How long do I let it go?

 

A hard code will be saved take it and get codes read! Cel was on meaning could of been a hard code.. I think a hard code has to be seen 3 time to leave light on?? I forget been awhile since I soon auto classes for that lol...

 

I will go through a few more cycles of running and maybe take it down the road and back

I had unplugged the injectors before to try n figure out what cylinder was skipping; right away it blew an injector code. I erased those codes and ran it trying to start over to get a good read.

 

So I have cleared the codes and warmed the jeep up twice and still runs like **** once it comes up go temperature and starts to skip. It still does not however blow a CEL for me to diagnose the problem(s).

I changed out the ignition coil pack (did plugs last week) and still same thing bring it up to temp and it skips and makes a knocking sound. I first thought knocking was spark knock hence doing the ignition coil.

Lost and needing my wheels back; any ideas or info appreciated

 

check vacuum
with scan tool freeze fram everything at start up then when it acts up n then come back on here and tell me whats different.

 

see if u get a code for iac. check all injector for proper voltage/resistance. with a scan tool u should be able to do an iac test also. is there any gauges reading off coolant? oil? etc... ive had it to wear the cts went bad and bad idle after warm up and eventually turned to hard start. bad mileage also happens cause engine is running rich

 

What is iac test? Coolant runs at norm temp on dash and scan tool. Cts???