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Juan Crespo
Juan Crespo, ASE Certified Technician
Category: Jeep
Satisfied Customers: 1522
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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2001 Cherokee. I've been chasing a missfire and shut off at

Customer Question

2001 Cherokee. I've been chasing a missfire and shut off at an idle for weeks. Numerous parts replaced. Coil plugs injectors. Fuel pressure is good. Harnesses checked. I'm lost here.
Submitted: 11 months ago.
Category: Jeep
Customer: replied 11 months ago.
I've also done the ecm. No used parts. All new. Plugs are fuel fowled pink.
Expert:  Juan Crespo replied 11 months ago.

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Well, I think we should take whatever information the ECM can give us to help us diagnose this stalling poblem; for example, we know misfires are about the worst thing that can happen, that's why the ECM will flag a corresponding code whenever it sees a misfire. Do you happen to know what that code or codes are?

Customer: replied 11 months ago.
Well before I worked on it in had a 301 303 and maybe one evap code.
Customer: replied 11 months ago.
Now it has none. But I did reset it. But nothing yet. However I have noticed the oil gauge seeming to spike on its own since plugs and wires have changed. It is moody and happens randomly. It stays spiked when it does act up leading me to believe that was electrical.
Customer: replied 11 months ago.
I ment plugs and injectors changed sorry
Expert:  Juan Crespo replied 11 months ago.

Thank you for that extra bit of information. Now, bear with me as I share my thought process on what could be happening; the ECM knows there is a misfire based on signals it gets from the crank sensor that tell it crank speed slowed down as a particular cylinder was firing. So what if the crank sensor was going bad and was no longer providing reliable information to the ECM? Could that be the reason why there are no current misfire codes?

Well, if on top of what I just stated, we add the fact that bad crank sensors are all too common on these vehicles, makes me think that's probably what we're dealing with. Why don't we give a new crank sensor a try and see what happens? Just make sure you get a good new part that comes with a felt or paper spacer and that you follow the install instructions in the box to the letter - no over tightening!

Please let me know how it runs afterwards.

Best Regards.

Customer: replied 11 months ago.
Yeah I hear that. I mean I've seen them come and go needing crank sensors. I've shook the wire a few times to make sure that it wasn't wiring. Do they really act intermittent like that sometimes? Sometimes this truck is great. Sometimes it's horrible and won't pass 5 mph. Sometimes the miss is only at an idle. It's wierd. When it does stall it's more like shutting it off then bogging down or choking.
Customer: replied 11 months ago.
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Expert:  Juan Crespo replied 11 months ago.

That's certainly what a bad sensor will do. It can drive you crazy because it's the computer's only source for those signals since there's no other sensor to compare crank speed or position.

Customer: replied 11 months ago.
Ok. I'll give it a go and let you know
Expert:  Juan Crespo replied 11 months ago.

Well, all I can say at this point is that I'm rooting for you. Go for it!

Customer: replied 11 months ago.
Juan...sorry I have been busy and haven't had time to post back. Crank sensor replaced with Mopar brand from dealer. No change. Took out champion platinum plugs which were still perfectly gapped and replaced with ngk. Probably 70% better. Dies at an idle still and it's very moody. Some days I can't sit at any lights. Some days I can sit at all of them. I know from this it's not mechanical and definately electrical. I shook all the harnesses to try and simulate a bad connection. Nothing. Only codes are the p0301 and p0303. That's it. Coil is new..but aftermarket. So I've ruled it out so far. But I'm running out of options here.
Expert:  Juan Crespo replied 11 months ago.

Is there any chance of you borrowing a scan tool capable of reading engine data so we can look at all the engine parameter id's when the engine is getting ready to stall? I mean, other than that, I'm just about out of options.

Customer: replied 11 months ago.
I'm going to ask my buddy tomorrow to borrow one. I'll get back to you
Expert:  Juan Crespo replied 11 months ago.

Please let me know.