At the end of June this year I began having issues with my 2000 XJ 4.0 running rough. Eventually one day I had just left home and it was like it had no power. Once it got warm it really started acting up. Once it got into high gear it would bog down at about 2500 rpm and had no power and would actually start to feel like I was putting the brakes on and I wasn't. It would spit and sputter like it was running out of fuel. The check engine light came on and began flashing. I took it home and parked it. Due to a rough year with the rest of the fleet of vehicles it wasn't looked at until December. We knew it had been sucking down antifreeze and thought it blew a head gasket. Turned out it had a cracked head. Got that all fixed up and drove it, nothing had changed. It idles great, no check engine light but when you throttle it up it didn't sound right. Could tell it was missing and then eventually the check engine light would come back on. The codes were for a misfire in 2 cylinders. After trying some other things, nothing improved and the same codes would come up for the misfire but it would be different cylinders then before. Here is a list of what's been replaced besides the new head .

cam sensor
idle speed sensor
timing chain
injectors
PCM
coil pack
spark plugs
probably a thing or two that I can't remember at the moment

any advice would be great. We are at a loss of what to try next. We are fairly certain it is an electrical issue

Thanks,
Andrew

 

A failing crankshaft position sensor can cause random cylinder misfires as RPM increase. I notice that is not on your list. Also, cheap after-market crankshaft position sensors have a reputation for this out of the box as well.

Since the crank sensor is not on your list, is that because it was already changed some time ago? perhaps coinciding with this problem?

 

I'd try changing the CPS. They have them for around $30 on Rock Auto I think.

 

I'd be wary of using any sensors on the XJ that aren't OEM. They're going to cost more but I've seen a lot of bad aftermarket sensors bad or way out of spec straight from the box. The Oil Pressure sensor is a great example of that. This forum alone is full of reports of brand new bad out of the box oil pressure sensors.

 

There was another thread about a dude looking at an 00 XJ with similar problems and it was mentioned that chafed wiring for the coil pack might be a real possibility.

Also, for some years (I think earlier though) there was a tendency for the CPS wires to come in contact with the exhaust, so that's another thing to check.

If it were me, I'd check the wires were all in good shape for the CPS and coil pack and if so, new Mopar CPS.

 

96 XJ 4.0 - The crank shaft sensor I bought from Rock Auto got me exactly 2.5 miles before it failed. RA is good for going cheap on some things but not with electronics. I bought the factory sensor and have had it installed and working fine for a year now.

 

You can often find Mopar stuff at good prices on Rockauto - you have to search by part number though.

It is widely stated on this forum that if you need a CPS, you really need a Mopar. There isn't another part that I can think of that is so widely agreed that it must be Mopar.
Someone mentioned that it the difference is in the magnet quality - aftermarket brands use a cheap and weak magnet that is not good enough for the Uber sensitive Jeep. You can often find a wide array of opinions and recommendations on OTHER parts, but for the CPS, it's Mopar.

I'll use Mopar if I can for anything that I need, but that's my personal preference. Ironically, (I believe it's because I drive a manual) the one part that I've never had or seen replaced in 707k miles of Jeepin' is the CPS...

 

It chafes on the back of the intake manifold. The CPS pigtail hooks to the wiring harness towards the back of the fuel rail. From there it goes down over the back of the intake manifold, where it makes that bend over the manifold it slowly rubs though the wiring loom material and grounds out on the manifold. Pretty easy to fix with some electrical tape and some more wiring loom if that is the problem.

 

Replaced the CPS and no luck. At a complete loss of where to look next.

 

Noid light for the injectors? Does the codes say which cylinders? Are they both on the same coil pack?
Have you tested fuel pressure and leak down?

 

if you clear the codes and drive it again, the codes come back for the same cylinder. The time
ing chain and cam sensor were out 180 degrees. After that was corrected the codes for the cylinder changed but has been the same cylinder since the timing was corrected. Fuel pressure is good and other then replacing injectors that's all that has been done to them.

 

Do you have 5v at the CPS TPS MAP CTS? How does the timing chain get out 180 degrees? Exactly what codes is it giving?




;

 

tick tick tick

 

Just an aside. It's bad enough Fiat has ruined Jeep's reputation, but now Mopar is having some of their parts made in Mexico.

 

Hecho en Mexico parts were a pretty common thing back when Chrysler was making XJs and RAMs and Durangos and what not.