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Old 03-19-2013, 10:10 AM   #1
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Fuel Pump? ECM?

I have an 02 TJ with 4.0L engine. Runs flawlessly, when it runs. It will randomly just stop running. No stutter, no bogging, no degradation of power, nothing. Just stops. Cranks right back up immediately when I turn the ignition and goes right along. Until the next time.

I had it pretty wet a few weeks ago and was thinking some water MAY have entered the fuel lines but a full tank of gas later and still doing it.

Fuel pump? Electronic control module?

Any help would be appreciated.

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Old 03-19-2013, 12:58 PM   #2
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A failing CPS can cause those symptoms. You might try cleaning and reseating the CPS connector.

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Old 03-19-2013, 03:58 PM   #3
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Help this computer geek out. CPS?
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Old 03-19-2013, 04:06 PM   #4
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CPS = Crankshaft Position Sensor. Mounted high up onto the driver's side of the transmission bell housing where it bolts to the engine, the CPS generates the engine's master timing signal. It generates the timing signal based on notches cut into the flywheel for a manual transmission or flex plate in the case of an automatic. When the CPS isn't functioning, the engine won't run... and the CPS can both go completely bad or intermittent where it can cause a problem like yours.

There is no guarantee your CPS is the root cause of your engine dying intermittently but it'd be the first place I would look as well. After that, I'd probably suspect a different CPS, the camshaft position sensor (on the distributor shaft) which can cause the same problem but is a little less likely to fail than the crankshaft position sensor is.
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Old 03-19-2013, 04:07 PM   #5
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crank position sensor

edit Jerry is too fast
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Old 03-19-2013, 05:32 PM   #6
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Fuel pump could be freezing. Replace the fuel filter. It could be clogged and the pump gets hot and quits.
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Old 03-19-2013, 05:39 PM   #7
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While fuel filters can get clogged in some vehicles, especially older models, the TJ's lifetime fuel filter has such an enormous surface area that it clogging would be the very last possibility that I wouldn't even consider. Modern fuel filters are no longer like the old small glass-encased fuel filters that easily got clogged up. The TJ's fuel filter can't even be changed separately without also changing the fuel pressure regulator it resides inside of. Not to mention the gas tank has to be dropped to even get to it.
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Old 03-19-2013, 05:42 PM   #8
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Originally Posted by pyrilampes View Post
Fuel pump could be freezing. Replace the fuel filter. It could be clogged and the pump gets hot and quits.
"Freezing" but getting "hot" and cutting off???

Anyways..,.,.. Jerry beat me to what I really wanted to post.
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Old 03-20-2013, 06:44 AM   #9
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Sorry, I forgot that mechanical failures dont happen to fuel pumps. And that old filters never clog.
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Old 03-20-2013, 07:05 AM   #10
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So the general consensus is in this order:

CSP
Fuel Pump

Any tertiary ideas? Trying to avoid taking it to a mechanic.
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Old 03-20-2013, 07:26 AM   #11
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Old 03-20-2013, 09:13 AM   #12
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Quote:
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Sorry, I forgot that mechanical failures dont happen to fuel pumps. And that old filters never clog.
Perhaps you did forget that neither of those conditions resolve themselves immediately.


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It will randomly just stop running. No stutter, no bogging, no degradation of power, nothing. Just stops. Cranks right back up immediately when I turn the ignition and goes right along.
Try pulling the fuel pump relay while the engine is runnng at idle and note what happens.
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Old 03-20-2013, 09:36 AM   #13
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Good luck fixing your problem, please update with any fix, I've been having the same problem for some time and nobody seems to know exactly what the problem(s) are. I have cleaned the throttle body, replaced the TPS, replaced IAC valve, and replaced CPS. I had a local diagnostics shop work on my Jeep, the tech told me that my Jeep only acted up once and when it did there was no communication between my computer and his, makes me think that maybe the computer is going out. No codes. The shop needs to be able to recreate the issue. I've noticed that this problem is more reoccurring when flexing. A tech at a Jeep dealer suggested that maybe a wiring harness is shorting. I don't have a fix yet. Laters,
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Old 03-20-2013, 11:27 PM   #14
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No error codes being thrown. At all.
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Old 03-20-2013, 11:28 PM   #15
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Good luck fixing your problem, please update with any fix,
I was chatting with a mechanic when you posted your reply. He's thinking a ground as well. I'll be visiting with him tomorrow at a social event so maybe we can narrow it down.

Thanks everyone.
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Old 03-21-2013, 10:13 AM   #16
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Has it died on you on the freeway? I have similar problem with an auto and it'll shut off for .2-1 second and turn back on if on the freeway. If going slow it shuts off and I have to restart it and usually cranks right back up. Happens 2-3x a week

Might be unrelated but I threw in seafoam last oil change and it stopped doing it until I changed the oil again.
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Old 03-21-2013, 12:58 PM   #17
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Has it died on you on the freeway? I have similar problem with an auto and it'll shut off for .2-1 second and turn back on if on the freeway. If going slow it shuts off and I have to restart it and usually cranks right back up. Happens 2-3x a week
Exactly the same thing. Seems to be a common Jeep anomaly.
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Old 03-21-2013, 09:24 PM   #18
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Yup. Very similar. I'm still feeling like its an ignition issue. I'm used to good old points, condenser, and coil. So I am not sure where to begin. THat will be another topic.
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Old 03-21-2013, 10:38 PM   #19
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I'm still feeling like its an ignition issue.
Quess what is at the heart of ignition control: the CPS.

The simple act of reseating the CPS connector has been known to cure the very symptoms that you report. The CPS generates very little voltage, so a slightly compromised connection can be very detrimental.
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Old 03-23-2013, 08:47 AM   #20
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Quess what is at the heart of ignition control: the CPS.

The simple act of reseating the CPS connector has been known to cure the very symptoms that you report. The CPS generates very little voltage, so a slightly compromised connection can be very detrimental.
Yeah well that's what I get for thinking. I haven't fixed it yet. But I have definitely ruled out fuel.

So... CPS and the PCM relay are next.

But a question. If it was the CPS wouldn't it be throwing an error code?
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Old 03-23-2013, 01:30 PM   #21
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Not necessarily the wires to my CPS melted on the manifold and it never threw a code, but ran like crap
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Old 03-27-2013, 10:38 AM   #22
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I spoke with a Cherokee owner Saturday, she told me that her rokee had the same exact issues I have described, she replaced and serviced everything I did as well as replacing the ECM, I turned out to be a shorting ignition switch. I will inspect this weekend; hopefully I'll find an issue, finally. Laters,
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Old 03-27-2013, 10:52 AM   #23
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So the general consensus is in this order:

CSP
Fuel Pump

Any tertiary ideas? Trying to avoid taking it to a mechanic.
I doubt it is a fuel pump issue, because your saying its abrupt. Fuel pump would create some bucking or signs of failure. Good chance its the CPS / Ignition issues
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Old 04-12-2013, 09:56 AM   #24
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Well... this is what I get for not listening to the experts. It finally threw a code and guess what. CPS. Thanks guys, sorry I didn't trust you.

Advance Auto parts... 35 bucks. 15 minutes work. Runs like a spotted ape.
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Old 04-12-2013, 10:10 AM   #25
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Glad you were able to fix it. I'll keep this in mind should I ever run into a similar issue.
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Old 04-12-2013, 11:48 AM   #26
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The uniquness of the situation as I described it makes sense now. It simply loses fire to the plugs and its immediate. No running like crap, no studdering... just OFF. Turn the ignition off and back on and it fires right up.

I thought fuel but as described about if it was a fuel issue, there would have been crap running before and maybe after.

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