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Check Engine Light Stays on

Old 02-19-2019, 09:31 AM
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Default Check Engine Light Stays on

I have a 1999 Cherokee XJ with a 4.0 auto. The check engine light came on and was throwing codes. I changed all the following, with all OEM parts, twice, replaced Cam, crank, TPS & engine harness, replaced all grounds. I have had two mechanics (one at Chrysler dealer and one independent) work on it, the light goes out for a day and then right back on. Removed distributor inspected, disconnected battery, cleared codes & starts right up. Now code P1391 comes up right away. So I removed inspection cover bell housing & made sure flex plate tight. The only thing left is timing chain, ECM & maybe pull trans. I am at a my wits end no matter what I try or change the light stays on. Not sure if this has anything to do with it, but I have added a large radiator and 3 electric fans for cooling.
Please help.

Last edited by Dogdays; 02-19-2019 at 10:00 AM.
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Old 02-19-2019, 10:05 AM
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How did the connection to the cam sensor look/feel? any green crusties? those cheesy chrysler red tab crappy locks break when you touch them, could it have come loose? could there be corrosion in that connector or the wire?
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Old 02-19-2019, 02:24 PM
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i bought a engine harness & had Chrysler mechanic install, light went out 5 miles & came back on, will pull connector & inspect, should this connectors be put together with dielectric grease? Or will that cause more issues.

Thanks for for the input
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Old 02-19-2019, 03:19 PM
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I try to use dielectric grease (in the form of silicon grease) every time i remove a connector... doesn't always happen in the real world tho. it just helps prevent moisture from turning the contacts into green crusties as you know. doesn't really help make a better connection. if the sensor is new and known good, and the connection is good and verified...same with the grounds. then you have to start testing from the ECU. Are there comms from ECU to CAM sensor... might be better with a chrysler scan tool. Have you checked out ScannerDanner on youtube? South Main Auto? those guys know their ****.

https://www.youtube.com/results?sear...m+sensor+p1391
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Old 02-20-2019, 04:45 AM
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What exactly does this mean?

Originally Posted by Dogdays View Post
I changed all the following, with all OEM parts, twice, replaced Cam, crank,
You've replaced the cam and crank twice? If so, there's certainly a whole different road you need to go down.

What's with this "Chrysler mechanic"? Was work done at the dealer? Did they use the Mopar scanning tools?

Did you replace the pick-up coil? How many miles on the engine? What symptoms do you have?

The PUC vs CPS debate:

Last edited by Dave51; 02-20-2019 at 05:00 AM.
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Old 02-20-2019, 05:00 AM
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Put a piece of tape over the light. Problem solved.
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Old 02-20-2019, 06:20 AM
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Originally Posted by Jimbo Slice View Post
Put a piece of tape over the light. Problem solved.
Right? I mean, I've got a P0141 that keeps popping up after a new sensor and checking all the connections, but the engine runs fine so AFAIC I'm not even wasting the time to go find the tape.
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Old 03-01-2019, 07:36 PM
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Glad I joined this forum itís been a great help. NOT
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Old 03-01-2019, 07:50 PM
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Originally Posted by Dogdays View Post
Glad I joined this forum itís been a great help. NOT
Have you answered the above questions to you?

I'd try unplugging the negative for 15 minutes to let the whole system discharge before I replaced all of the engine harness. If you still want help, then please reply that you still want help. When I don't read answers to question, then I assume that you have stopped posting. Try discharging the system and report back...
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Old 03-01-2019, 08:04 PM
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Originally Posted by Dogdays View Post
Glad I joined this forum itís been a great help. NOT
You might pose the question over on the NAXJA forum. I find there is a bit more expertise over there, and less drive-by postings about "I just replaced the headlights and now my brake lights don't work" and nonsensical answers like "put a piece of tape over it" posts. Anyway, it sounds like you've already tackled the usual suspects so I don't have much more to offer than perhaps trying to pickup a spare ecm or distributor for cheap and seeing if that changes things. Some folks have reported clearing up intermittent crankshaft position sensor issues by bending the bracket slightly to put it closer to the flywheel. As an even more left field suggestion, check that the bellhousing bolts are tight.
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Old 03-02-2019, 04:10 AM
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Originally Posted by Dogdays View Post
Glad I joined this forum itís been a great help. NOT
Well, I asked a bunch of questions to try to get some clarification, because your post is not clear. Incomplete information = incomplete responses.

IMO there's 3 paths on this diagnostic tree, but a "Chrysler mechanic" would have done that. But strange you said "Chrysler mechanic" and not "brought it to the dealer". Was this a self-proclaimed "Chrysler mechanic"?

Good luck at NAXJA.
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Old 03-02-2019, 04:58 AM
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Originally Posted by Dogdays View Post
Now code P1391 comes up right away.
What were the previous codes? Ask your mechanics to hook up to their dealer scan tool. They will be able to see the sensor square wave outputs and graph them. You can see if it is constant or intermittent that changes with rpm.

After that has been done if the issue is still unfound inspect the timing chain. Check for distributor alignment. Inspect the distributor gear teeth.

Where are you at price wise with total parts purchased, just a rough estimate?
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Old 03-02-2019, 05:03 AM
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Originally Posted by Cummins93 View Post
Where are you at price wise with total parts purchased...
And are they Mopar parts or ZhŪ shǎizi parts.
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Old 03-02-2019, 11:57 AM
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Originally Posted by Cummins93 View Post
What were the previous codes? Ask your mechanics to hook up to their dealer scan tool. They will be able to see the sensor square wave outputs and graph them. You can see if it is constant or intermittent that changes with rpm.
I agree, scoping the sensors is a good next step since it's consistently throwing a code when started. It's the intermittent ones that never act up when you're troubleshooting that are a ***** to track down, which tends to cause the shotgun approach of replacing parts until it behaves. If it's the timing chain, I'm not sure how far off that can be to cause the code but still run okay. I haven't seen any cases of the timing chain causing this myself. Most of the time it's the crank sensor, and sometimes a new offbrand one is bad out of the box.

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Old 03-02-2019, 06:20 PM
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Default Check engine light

ive discharged the system multiple times, ground positive turn on headlights to drain power. Even have left battery disconnected for over a week, connect starts right check engine light comes on Rightaway. Then over a weeks time of driving slowly is harder to start. Iíve checked fly wheel bolts & are tight
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