Hey guys! Been a couple years since I have had any trouble and got on here. For any of you folks that have been around I am the guy that did/went through all this:

https://www.cherokeeforum.com/f5/cyl...-4-0-l-220211/

You guys were so helpful and I have came back silently over the past couple years to look for minor stuff... so I think what I learned today needs to be shared so hopefully it will help someone else. There is a TLDR at end for those of you that don't want to read through all of this. There is a lot of info here

So my jeep is a 2002 WJ but the crankshaft sensor on mine will be the same on xjs of similar manufacturing year (don't know exactly) so I will share here anyway. I had noticed last month that I was getting a little hot when idling for a long time. Not much, but over the midway mark which never happens. It had been a while since I had added some coolant (like over a year) and I had repaired a crack on my radiator near the cap with epoxy putty so I shrugged it off because the temperature stabilized once moving.

ANYWAY my jeep started dying. Sometimes when stopped. Sometimes when going 20-40 down the road. Sometimes the intake would backfire, sometimes it would sputter, sometimes it would just go *click* like someone hit a lightswitch. I got to googling it like most folks and the crank sensor started popping up. Rewind to the disaster a couple years ago that I documented in the link above, I had bought sensor after sensor for this think hoping it would fix my misfire. I remember the ONE I didn't do was this one. I got a really good look at where it is located and thought to myself "I think I'd rather just pull the head back off".

I still needed to work and I live/work in a small town so I would just cruise down the road, it would die, I would nonchalantly throw it in neutral and crank it until it started back up, put it back in drive and keep going. I did this for two weeks until it finally got progressively worse and worse. It was time.

I went to the local auto parts store. They are a locally owned, single-location small town store but the inventory these guys have is unbelievable. More than the big chain places. I asked about a MOPAR sensor since everyone on the internet is adamant about using one instead of a generic. The MOPAR one would take a few days and they would have to order, cost around 100 dollars OR they had a cheapie for 25 dollars in stock and a higher quality one for 45. I needed to get back to work ASAP and can't without it so I got the better one.

So this thing was a real mother f***** to get off. First note that the transmission linkage in the way that has to be moved out of the way: the little connector at the end of the steel cable just pops off of the ball it sockets on. I was so terrified of breaking it and looked and looked on the internet until I finally took a flathead screwdriver and wedged it between and twisted. Popped off and didn't break.

Now that 11mm bolt. There is a larger bolt just beneath it but if your jeep is like mine there is all kinds of dirt and grime raining down straight into your eyes as you are working so you have to feel around for it. It is very easy to mistake the larger bolt beneath it for the 11 mm above you are trying to get to when you are just "feeling around". I used a craftsman 3/8" ratchet, long extension, pivot extension with some duct tape around it to help keep it rigid, short extension, then a long 11mm socket. You have to do this funny wobble back and forth but once you get the rythm going you can eventually just get it with a 1/4" hand driver or with your fingers. Took me about an hour and several swear words to get it off the first time.

There is a little bracket on top of it. The haynes manual says wire harness mover out of the wayer bracket or something? Idk it didn't look like it was doing anything but it was between the sensor and the nut. Pulling the OG sensor out was kinda tricky. I have big wrists and couldn't twist my hand around. I had to reach up over the housing on the pre-cat side before I could get my hands on it. You have to pull it out and twist it counter clockwise as if you were looking straight at the wire/connector end of sensor. The whole sensor was pretty filthy. My main seal, oil pan seal etc have been slowly leaking for years and there is built up grime, pretty thick in places, all over the bottom including the area with this sensor. My hands were pretty dirty but the sensor itself seemed to have a layer of filth of its own on there. I attached a couple of pictures of what I suspect is the factory crankshaft sensor. Mind you I had cleaned it earlier.

Pretty basic looking sensor. The only difference that stuck out was the piece of paper on the new one. I had a hell of a time putting in the replacement. Trying to blindly find that hole and go in at the right angle is tricky. When I was tightening the bolt I started having trouble getting my socket onto it. I tried and tried and finally stopped and got a flashlight. That wire something or other bracket had torqued around and folded over the top of the damn bolt. I was pretty furious so I bent it back and forth until it broke off. Tightened the sensor down, put everything I had torn apart in the engine compartment put back together, new coolant and thermostat and then....

Wouldn't even start.

Hell even with the worn out sensor it would start and stumble down the road. Even with all the folks saying not to buy generic I refused to believe that this one COMPLETELY doesn't work right out of the box.

I go to reading crap on the internet and all signs point to "buy another sensor". I did find a thread somewhere that a guy says the paper spacer COMES OFF when you turn the jeep over and that it doesn't hurt anything inside. I very reluctantly pulled the sensor back out and looked and it still had the paper spacer along with a bunch of engine grime all over. I got a closer look at the spacer and it is about the thickness and consistency of matchbook cardboard. When you push down on it it's a little spongy. Then I realized the reason the bolt hole is slotted is because you have a tiny bit of play in and out before you tighten the sensor down. I put it back in. This time before getting tight enough to make the sensor immoble I jammed the sensor as hard as I could in its slot.

And wouldn't you know. It started right up, idled about 600 rpm, didn't backfire at all.

Now to all of the folks out there that know from experience to buy Mopar, I do need to say that when I was driving it around to work the air bubble out of the cooling system I noticed it would lose power when flooring it all the way. Not enough where a passenger would notice but a daily driver of the vehicle would. I do believe this is a product of the aftermarket sensor. Also I cannot say anything of its longevity since I put it on less than 12 hours ago.

So

TLDR; When putting your replacement sensor in, PUSH THE SENSOR DOWN HARD IN THE SLOT SO THE PAPER GETS PUSHED AGAINST THE CRANKSHAFT. I am still going to buy the Mopar sensor but this way I can work the rest of the week and weekend at the very least.


Now my electronics background wants to inspect the old aftermarket sensor to see if I can visibly find what was going bad with it. If I find anything interesting or useful I will post it on here.

 

Take the aftermarket sensor, and a new mopar sensor, and hold a steel bolt up to each. What you will find is the bolt will stick much harder to the mopar one. This should explain the difference.
Thanks for the TDLR.

 

The WJ has an access hatch in firewall for changing CPS from inside the cabin. Have to remove a lower portion of dash and airbox to get to it however.