GanderThePanda

Exert from my Build Thread for my Jeep Cherokee XJ 98

This post is mainly to get suggestions on what to check next, I'm a novice so I may be missing obvious things to check for others.

So today I decided to let the jeep run for a while as it's been a couple of weeks since I last started it. Turned the key, engine turned over and the jeep started! After around 4 seconds it died. I turned the key again, but it would only crank.

After a fair amount of research many people report this symptom as a Crankshaft Position Sensor issue.

I tracked down checking this sensor in my haynes manual, and it said to check continuity between pin B and C. And there should be unlimited resistance. I measured mine and I got a continuity reading of 800. Which indicates to me a bad Crankshaft position sensor.
For those of you reading who also have this issue, I found through limited information that people suggest staying away from after market parts and only buying OEM (Mopar). I had also read people have had success with Standard Motor Product P308 and also NTK. I've ordered the former and will see how it goes.


I also read my engine codes again for the heck of it, (whilst I'm speaking of engine codes, I think someone removed the light indicator as it's never come on) and low and behold I have a new code.

CODE P1391
Loss of Cam or Crank Signals.

After some research of this code, it can also be caused by a number of things. Having already diagnosed the issue, I'm going to replace the sensor and go from there.

I'll update when it arrives.

UPDATE 1
Changing this sensor was a major pain in the ***.

You will need an 11mm socket with a swivel and a 20" extension.

Unfortunately it's very difficult to photo anything on the trans. So I'll attempt to describe the process.

This particular sensor is located on the drivers side of the trans. You can actually see it if you look behind the engine. You can trace the connector you'll need to disconnect from there.

Other than that have fun! Try your best not to drop the bolts holding the sensor into your transmission or you're gonna have to drop the trans to get that out.

After spending about an hour of trying to install the new sensor, make sure you're in the correct bolt hole... There are 2 very close to each other.

Unfortunately, replacing the sensor didn't solve this issue. Since it's been sat for around a month, my battery is very flat (lower than 50% charge) regardless that its still cranking.
I'm going to recharge it to 100%, try starting again and then start diagnosing Spark and Fuel issues. Working on Power Scooters and Wheelchairs has always taught me to start at the battery and work your way out from there, saves you from simple electrical issues.

UPDATE 2
So after charging my battery to 90% I tried starting her up, she started! And then died within about 2 seconds and wouldn't start again. I'm going to buy a mopar sensor and try once more. The consensus online is oem is best for the cps.

UPDATE 3
For the heck of it, I thought I'd check my engine codes again, and something interesting happened. The old P1391 code was gone, and was replaced with P0320 "Crankshaft Position Sensor Circuit". This almost confirms that the aftermarket sensor was the issue in my opinion.

UPDATE 4
So the mopar sensor has seemed to have helped, the jeep starts now but immediately stalls. Still reading code P0320 on the computer. I'm looking at changing the distributer pickup coil or camshaft sensor next as that sensor seems to be connected to this error code from the research I've performed. Wish me luck! any suggestions would be appreciated.

Roler

If so, change the CAM sensor first. Easier and cheaper.

But:
check fuel pressure and alternator output.
Btw: if your battery has been flat for a long time, good chance it's gone bad, despite it maybe showing 'enough' voltage. Have it load tested.

GanderThePanda

It was flat for about a month, and it is a 5 month old battery. I then recharged it.
I have a load tester at work, I'll try it.

GanderThePanda

Load tester tested good.

Whilst in there I looked at the distributer, and noticed that the wiring between the cam sensor and connector had been soldered together at some point. Now I'm starting to suspect it a lot more. Part will be in Tuesday, will update.

I hear the fuel pump prime so I'm doubtful its that, but the gas in there is getting old now... its at least 5 months old.

Will check alternator next if this coil doesn't work.

Dave51

Wanna borrow my oscilloscope?

GanderThePanda

Appreciate the offer dave, but looks like you're on the other side of the continent to me. I'm near Calgary.

How much are one of those oscilloscopes? Might be useful in future.

Dave51

About a hundred bucks.

Dave51

But you can see what's happening to both the CkPS and the CPS. Besides being there, they also need to be in sync:

Dave51

This reminds me of the loose transmission bolt story. Take a look anyway:

https://www.cherokeeforum.com/f2/fue...253246/index8/

GanderThePanda

How do you plug it into the car? Excuse my lack of knowledge ...

I'm pretty bad at electrical stuff. But learning as much as I can! 😅

Dave51

Looking back, perhaps we should have blown up the CkPS signal there. I believe the reason only Mopar sensors work is that there is a slight deviation in the signal duration. Read that somewhere. Damn, shoulda saved that...

GanderThePanda

Interesting! I'll look at those when I'm next rolling around in the enginebay. I'm actually planning to drop the tranny to fix a leak coming from the bell housing area.

GanderThePanda

Also interesting! May be why my jeep starts momentarily with the mopar sensor.

Dave51

Check to make sure the flexplate isn't loose bent or broken.

Dave51

Just take the signals from the CkPS and CPS, grounds, and voila!