I have been trying to figure out the reason for my cylinder 3 misfire. 2001 xj 4.0. I got my misfire about a month ago. It is not a heat soak issue. My misfire happens all the time. I started with replacing the wiring connecters because they were brittle and cracked up. That did not fix it, then i moved on to upgrading my injectors to 12 hole Bosch ones. That seemed to fix my issue for about 2 weeks. Yesterday my misfire started on cold startup. It was running perfectly fine until yesterday. I have looked throughout the wiring harness for a broken or exposed wire tracking from the pcm to the injector. No problems with the wiring. Then i swapped my #3 and #4 injector to see if the misfire moved. No luck still the same misfire on #3. What is my next move since it is not a wiring issue nor a fuel injector issue?

 

If you swapped injectors, but the misfire didnt follow, it only indicates its not the injector ITSELF.
Wiring to/from remained the same.

In general: If its not the fuel side, check the spark side of things (it takes both for proper combustion), assuming here your compression is good (which you could easily test with a gauge). Most misses come down to one of those issues.


Check fuel pressure
Check for good strong spark
Check compression

Those three will give a lot of info, especially if you say it misses all the time. Intermittent misses on thr other hand can be a pain to diagnose.

Just my initial thoughts, worth 2 cnts

 

Could be the injector driver. Got a PCM to change out?

 

even though it is giving me a fuel injector misfire code, could it be the spark? Coilpack maybe? I thought if it was spark related a specific code for that will be present? Thanks for the help

 

pcm was my next guess but they are expensive and I don’t have a soare

 

Get some noid lights at AZ to confirm it's the injector.

 

Circuit.

 

Checked connecter with a noid light at work. No light at all. No flash or anything. All 5 other connectors were flashing good. Seems i have no power to the injector

 

OK the injector should have power all the time. The circuit is completed when the PCM driver grounds out and the injector fires. If you have NO power to the injector that's good cause it's a bad wire or connector. If you HAVE power but the noid doesn't light that's bad cause it may be the PCM (or the wire from the injector to the driver).

Feel like taking the PCM apart? The pins inside the PCM for the injector driver could be broken and simply need resoldering.

 

So with your multimeter check to see if one side if that injector has voltz.

 

okay i will do this next and yes i am good at Soldering so I have no problem taking apart the PCM. Just would need to know exactly what pin to re-solder.

 

Checked connector with Multimeter and I’m getting 12 Volts to the connector

 

From the 2000 FSM:

 

 

I have hardly ever had any codes, whether it was CPS going out, CAM sensor, cylinder 1 misfires etc. Got used to not having any help from the CEL

There is a good lead to find the cause. Dave51 is already on the trail with you.