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Unread 06-16-2012, 05:33 PM   #1
kel-uk
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erratic idle after replacing crankshaft sensor??

so after diagnosing my non-starter with help from this forum, i replaced the crankshaft sensor and yipee she sarts!

however........... now the idle is 'hunting' (term my mechanic used?!) and sometimes misfiring. the revs start at 800 - 1500 jumping up and down and gradually work its way down to 800 and lower until it drops off completely and cuts out.
we've tried unplugging sensors but none make a difference.
if i press the accelerator the revs go up to the right amount but continue to jump up and down, same when i try to drive it (both times it cut out when i took my foot off the accelerator but started again straight away).

we have checked all leads, pipes etc.

can anyone please recommmend what we should do next to diagnose the cause?

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Unread 06-16-2012, 08:53 PM   #2
ratmonkey
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brand of crank sensor?
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Unread 06-16-2012, 09:45 PM   #3
KoreaZJ
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If your new crank sensor is good, then perhaps throttle position sensor.
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Unread 06-17-2012, 06:45 AM   #4
kel-uk
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brand is blue print. its the only brand i could get hold of here in the uk but it is trusted by my local garage where my mechanic works.

is there any way of checking TPS to pin point it before purchasing a new one? all my dials etc are working as they should so cannot check it like i did the CPS by unplugging until something happens.

cant understand how it was running perfect, died, replaced CPS and now something else............ or is this a case of "you know you own a zj when...................!!!!"
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Unread 06-17-2012, 08:01 AM   #5
ratmonkey
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well, zj's do not like sensors that are not OEM. even the most trusted parts store brands will do that with the main sensors on a zj.
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Unread 06-17-2012, 08:21 AM   #6
KoreaZJ
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Did you disconnect the battery when you replaced the crank sensor?
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Unread 06-17-2012, 08:36 AM   #7
JasonStebbins
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I'll have to agree with Rat on this one. Blue Print is just another foreign parts distributor that won't get along with ZJ's.

http://www.blueprint-adl.com/
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Unread 06-17-2012, 08:39 AM   #8
KoreaZJ
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At least his runs! My last non-OEM crank sensor wouldn't even fire.
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Unread 06-17-2012, 09:08 AM   #9
kel-uk
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yes i disconnected the battery and left it off for over 12 hours while i charged it. wouldn't the CPS cause the dials not to work again though?
is there any way i can test it?
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Unread 06-17-2012, 08:45 PM   #10
ratmonkey
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Disconnecting the battery clears the adaptive memory. Give it a few miles of driving to see if it learns again.
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Unread 06-18-2012, 12:07 AM   #11
KoreaZJ
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Quote:
Originally Posted by kel-uk View Post
yes i disconnected the battery and left it off for over 12 hours while i charged it. wouldn't the CPS cause the dials not to work again though?
is there any way i can test it?
HERE
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Unread 06-18-2012, 12:45 PM   #12
GuydeLoimbard
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I had the same sort of problem with a brand new (carquest) crank sensor. After I put the new sensor in, it would only fire cylinders 1, 4, 6 and 7. Replaced it with a second new one and it was alright after that.
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Unread 04-08-2013, 04:12 PM   #13
kel-uk
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well, just to update you, after much searching i could not get hold of a mopar sensor here in the uk so purchased (at 3x the cost) the cps from Jeep. this also didnt work!! i resorted to buying a secondhand one from a scrap yard and it is doing the job perfectly!!!!
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Unread 04-08-2013, 09:03 PM   #14
jeepyard
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Had the same problem with an 01 square cherokee 4.0. It was randomly stalling so I ran to my local parts store and got a new crankshaft sensor and put it on and it misfired for the first 10 to 20 seconds after starting it and it starting throwing a check engine light. Next day ordered one from the dealer and put it on and it was perfect and no problems. Took the other one back for a refund!! Jeeps dont like aftermarket sensors for sure!!
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Unread 04-09-2013, 02:59 PM   #15
Exdecuk
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^^^ x a million.

Only use factory sensors which ever ones you need to stand any chance of being in the ballpark. I have a spare of every sensor (engine) here for the 9er which may seem like overkill but you just gotta have one go out and if the garage doesnt smack your *** in labour they will do it for the part cost over here. Its cheap insurance for the V8 as they are rare here.

What makes it even worse is on the V8 its such a PITA to replace the crank sensor and have to do it TWICE is just a horrible thought I presume the 4 slows are easier to get at
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