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I need your opinions guys
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Hammer Time
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Jul 21, 2009, 9:47 AM
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I need your opinions guys
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I've got a 99 Grand Cherokee 4.0 that was towed into my shop today. It starts up fine, runs fine for about 5 - 8 seconds and then like clockwork, it drops injector pulse. It has coil on plug so it's hard to check spark but I seem to be able to keep it running with carb cleaner so it appears the spark is holding. Cranks signal, 5v reference and ASD seem to stay alive until after the death. I also noticed the scanner lost communication after every stall. I'm thinking it has a bad PCM but I'm not overwhelmed with confidence and the PCM is $700 plus flashing. It had a cam sensor code in history but I cleared it and it hasn't come back after the truck died at least a half dozen more times. I have a cam sensor coming in the morning but I'm not expecting anything from it.
What do you guys think?
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zmame
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Jul 21, 2009, 10:59 AM
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Possibility of water entering the PCM?.. not sure about dodge i know on fords its common problem because of there location. it can cause all sorts of weird stuff.. hard to say with out looking at diagrams and getting right into it.
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Hammer Time
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Jul 21, 2009, 11:04 AM
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This is a sealed PCM mounted in the engine compartment.
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zmame
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Jul 21, 2009, 11:24 AM
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Other then that checked a 4x4 forum i'm registered with too they seem to be common for CPS (which you said is ok).. and there is a ground at rear of head. It is a braided metal strap that runs from the motor to a ground point on the upper driver side engine firewall. If it's frayed / broken it can cause all kinds of intermittant wierdness (stalling/stumbling/electrical issues).
seems to be common problem though
there was another guy on there with a 97 with similar problem he found:
Quote:
FOUND THE PROBLEM!
Found that the outboard PCM cover screw was shorting out the circuit board. Chrysler PCM p/n P56028412, s/n TEH106636023.
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Hammer Time
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Jul 21, 2009, 11:29 AM
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This is not an intermittent or random problem at all. It will shut off at the exact same moment every time it's started. It's completing some kind of timed cycle and then stops injector pulse.
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zmame
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Jul 21, 2009, 11:31 AM
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thats the issue guy was having with PCM troubles.. also there was one on there start and stall within 10 seconds or less ended up being CPS. ground just be a quick easy thing to check
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Hammer Time
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Jul 21, 2009, 11:35 AM
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I already tested the CPS during the failure and it stayed alive while the engine was dying.
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zmame
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Jul 21, 2009, 11:42 AM
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Probably lean toward PCM, but costly like you said and really just guessing.. i assume Chrysler is like ford where you cant send back electrical items once the box is opened. The guy with PCM problems on message board about PCM shorting out had no communication. so don't think shorting would be the issue. have you done pinpoint test from CPS to PCM?. maybe bad wire?.. hard to say
sorry couldn't help anymore.. ill leave you alone now lol
(This post was edited by zmame on Jul 21, 2009, 11:43 AM)
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Loren Champlain Sr
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Jul 21, 2009, 1:11 PM
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Hammer; Sounds like classic crank sensor failure. Also, check the PCM connector. We've had two where the OPS leaked oil into the harness and 'wicked' oil into the PCM.
Loren
SW Washington
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Hammer Time
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Jul 21, 2009, 1:14 PM
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I monitored the crank sensor while it died and it stayed alive till the engine completely stopped but the injector pulse quit right away. I also believe i still have spark and ASD so that would rule out the crank sensor.
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Sidom
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Jul 21, 2009, 4:24 PM
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All the older JTECs (& SBECs) requires the the ckp & cmp to start, some only require the ckp to stay running. You can try disconnecting the cmp while it's running, if it stays running & doesn't die any more then the sensor is shorting out when it gets hot. Not only will it pull down the ref voltage & it can pull down the PCM as well......
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Hammer Time
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Jul 21, 2009, 8:53 PM
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Since I'm working alone, it's about impossible to unplug the sensor in the 5 seconds it stays running but I'm going to try another Cam sensor this morning. I don't have high hopes for that though.
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