I'm at my wit's end with my 1999 Jeep XJ 4.0L that has experienced a misfire that has become progressively worse over time. At idle, the RPM bounces around significantly and the engine gets very close to stalling -- and has actually stalled one time. This is much worse with the A/C on.

I've taken a video of what happens -- apologies for the bad focus, but hopefully you'll still get the idea:

Current codes are P0300, P0301, P0303, P0304 -- these come and go as well as various other misfire codes after clearing them.


Unfortunately, I'm very busy during the day and rarely have time to take this to a mechanic, so several of my attempted fixes have been nighttime "spray and pray" part swaps based on research I've done online. However, even when I have taken it in, my two trusted mechanics have run completely out of ideas and one even went as far as to suggest that it may be a clogged catalytic converter (exhaust shop removed converter, tested, and eliminated this) -- or a bad valve within the engine, head gasket failure, or something else that's horrible and costly.

Changes thus far:
- New plugs, wires, distributor
- New Bosch 4 pin injectors
- New MAP sensor
- New Oxygen sensors (to address O2 sensor codes)
- New throttle position sensor

I've done a bit more research and can see that some people had similar issues and replaced the Crankshaft Position Sensor to address this. I mentioned this to my mechanic yesterday but he said to not bother because the CPS wouldn't cause this kind of problem. He is "90% sure" that I have early signs of engine failure and that I should get rid of this thing to save what's left of my sanity.

This is my weekend driver that I'd love to get running again. What do you guys think?

 

You replaced the distributor?


Try replacing the Camshaft Position Sensor (Switch Plate) in the distributor. It's the thin black plastic disc below the rotor, with a wire connection.


Also, examine the cam sensor wiring going to the cam sensor for chafing/bare wires, and inspect the cam sensor connector pin cavities for corrosion.


While you have the distributor cap off, check for excessive rotational play in the distributor shaft by twisting the rotor back and forth.

 

Sorry, long night. We replaced the cap and rotor -- not the distributor. I'll take a look at the camshaft position sensor but I can't seem to find a replacement part number at RockAuto, Oreilly, etc. We're talking about this one, right? http://upload.removed.us/images/8328...4782314376.jpg Any thoughts about the Crankshaft Position Sensor? Which should I replace first? Thanks again!

 

Thinking this would not apply but throwing it out there anyway. I know in '96 with a 4.0, from a buddies ordeal with his, that the temp sensor in the thermostat housing will mess with how the Jeep runs. His was running like crap. Figured tune up. Did a complete one including the fuel filter and still ran like crap. Took him awhile but he finally figured it out.

 

The OEM part number for the Camshaft Position Sensor (Switch Plate) is 56041030.


For some reason, it's called a Distributor Pickup Coil by the aftermarket pukes.


http://www.rockauto.com/en/partsearch/?partnum=56041030


At this point, I don't think it's the Crankshaft Position Sensor.

 

Thanks for that! I'm looking to pick one up from O'Reilly today... two results came up: http://www.oreillyauto.com/site/c/de...yword=56041030 & http://www.oreillyauto.com/site/c/de...yword=56041030 It looks like just a difference in harness length (and $20!) between the two. Any opinion which one to go with?

 

Perform a compression or cylinder leak down test.

 

You need the 2-6220. Flat pin OBDII configuration.


2-6211 is a round pin connector.

 

I had a similar issue with a rough idle and P0301/PO305 codes. It ended up being an issue with the coil, which I replaced along with the cap, rotor, and plugs. The thing was a pain in the *** to remove but the truck is now running perfectly again.

 

I pulled the negative terminal cable, installed the BWD #ME658 (similar to what was linked before, but available locally & lifetime warranty) and I'm sorry to say that nothing has changed.

Another YouTube video:
https://www.youtube.com/watch?v=u9Ym...ature=youtu.be

"While you have the distributor cap off, check for excessive rotational play in the distributor shaft by twisting the rotor back and forth."
No noticeable play when testing this.

"Also, examine the cam sensor wiring going to the cam sensor for chafing/bare wires, and inspect the cam sensor connector pin cavities for corrosion."
I didn't see anything that stood out. I could spray some electrical contact cleaner inside (didn't have any handy) but nothing seemed out of place on the connector or the old sensor while I worked on this.

Thanks!

 

You might try inspecting and testing the ignition coil, as squalor_victoria, implies.


The coil does not have to be removed to test it, provided you use test leads as shown in this link.


Any cracks in the coil is grounds for rejection. Resistance out of range is grounds for rejection.


Open this link and look at each picture (click the image to enlarge).


https://www.cherokeeforum.com/g/album/5065328

 

I think I may just replace the ignition coil -- it'll probably be faster than getting my multimeter going again, which is a piece of junk to begin with.

Will this one work? My XJ is a 1999 and does not have the large coil pack with COPs.

http://www.oreillyauto.com/site/c/de...=ignition+coil

 

That's it, but look at what NAPA has to offer. I'm not a fan of BWD, master pro, or their ilk. I think NAPA may have an Echlin product. If not go for the O'reilly one.

 

NAPA had no local stock of the ignition coil so I went with O'Reilly's. This looked easy at first but working with the two fasteners that hold this in place ended up taking over 2 hours -- including a trip to Auto Zone to replace a nut that was lost and could not be found despite every inch of the engine bay being poked with a magnetic doohickey.

On my XJ, one side of the ignition coil has a nut that is a hair away from one of the motor mounts, and the other side wasn't much better - even with several ratcheting wrenches in use. Getting the old one out too the longest but after removing the coil, it became quite obvious that this was the problem:

http://upload.removed.us/images/9168...2958426909.jpg

I've taken the XJ on a 4.5 mile test drive with lots of stopping, idling, etc., and she hasn't misfired once so far. Thanks so much for the help!!

 

Good work.


I added your top photo to my coil testing album.