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Unread 02-16-2013, 02:19 PM   #1
PaYj
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no start

ok there is a long story that goes along with this but for time savings i have a 96 4.0 GC, i have no spark, i have tested for power at the coil and when i turn the key on i do have power, what i do not have is the pcm controlled ground, now everything i have read says crank position sensor, so like a dump ars i went to advanced and got one, well still no spark, so i broke down and purchased a mopar one. installed it and still have no spark, so whats the chances i got a bad ckp from mopar, i tested the one from advance and it has resistance from terminal B to C, which means it bad, but i didnt test the new one from stealership before installing it, now i just went outside after looking at the test again i though heck why not, so i tested it and it has 1 m oh resistance, everyone says it should be a open circuit which i assume on my meter should read OFL. Now i took the advance ckp and hooked it up the the connector and when i wave it past a metal object i can hear the ads relay and evap can clicking and i assume injector pulse also. Can someone maybe shed some light on wth is going on here am i overlooking something super simple or does my zj hate me

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Unread 02-16-2013, 07:38 PM   #2
ZeeJay1997
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FWIW, The PCM sends an ignition pulse to the coil, it's not a direct ground.

Does CEL come on for three seconds when you turn the key on?

Does the fuel pump run when the key is turned on?
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Unread 02-16-2013, 10:54 PM   #3
PaYj
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correct, sorry if i made it sound direct, the pump and cel both turn on like they are supposed to, i went through the dirty dozen link that you have in your post and i am just dumbfounded that i cant figure this out, i was a motorcycle and diesel tech for years and this dam jeep put me in a corner and spanked me
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Unread 02-16-2013, 11:45 PM   #4
Rich93ZJ
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Im confused. If you have power going to the coil and nothing going out of the coil, I would say the coil is bad
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Unread 02-17-2013, 12:00 AM   #5
ZeeJay1997
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the meg ohm on the crank sensor going one direction is normal. It has some electronics in it that block current.. I believe red on outside and black in the middle is where you want an open circuit. IRRC, if you look at the voltage across the coil connector pins while cranking, you should see somewhere around half the battery voltage. From GN/BK to negative battery should read battery voltage.

The best way to be sure your crank and cam sensors are working is to back pin the signal wires and use an analog meter to see if the 5V pulse is generated when the field collapses. If they are both producing a signal, the problem is elsewhere.

The coil drivers in these PCMs are known to fail. Some of the reman vendors replace them in all units.
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Unread 02-17-2013, 11:03 AM   #6
PaYj
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the coil is new but actually the coil has power to it will cranking and running but the ground is given to the coil by the pcm, if i do not get that ground i dont get spark

Zee yes that is about what the voltage is while cranking at the coil on the GN/OR i believe it is,, i will have to pick up a analog meter as i have digital and it will not react fast enough the the field collapse. I was wondering if i hook a test light up to it will i be able to see it or again is it so fast that the light will not actually fully light?? either way i will go get a analog meter and test it like that.
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Unread 02-17-2013, 11:38 AM   #7
ZeeJay1997
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I recall that I used the AC function of the digital meter to look at the low side of the coil voltage. Since it is a DC square wave, the AC meter will read it as about 8V IRRC. It's been a few years. Something to think about anyhow.
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Unread 02-17-2013, 12:10 PM   #8
715raccing
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Just went through all this in depth.
The ECM grounds the coil,providing the pulse to the primary side.
If that's not happening and the shutdown relay is not enabled,it won't spark.
My money is on a bad driver circuit in the ECM.
Try probing either side of the coil power with a test light and see if it's pulsing while cranking.If not the circuit is not grounding.
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Unread 02-17-2013, 01:17 PM   #9
PaYj
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Quote:
Originally Posted by 715raccing View Post
Just went through all this in depth.
The ECM grounds the coil,providing the pulse to the primary side.
If that's not happening and the shutdown relay is not enabled,it won't spark.
My money is on a bad driver circuit in the ECM.
Try probing either side of the coil power with a test light and see if it's pulsing while cranking.If not the circuit is not grounding.
thats what it seems like is happening, i cant see a brand new mopar sensor being bad out the box, i went to the junkyard and pulled a used pcm and still got the same thing, so either i got a bad pcm with the same problem or its something else, its about 10 degrees outside, but the asd relay seems to be working because when i crank it to do the test i can smell fuel, and when you first turn the key on you can hear it click when the pcm is giving it its momentary voltage
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Unread 02-17-2013, 02:25 PM   #10
minimika2008
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I went through kind of a similar problem recently and replaced a crank postion sensor that wasnt bad...when you turn your key on are your gauges working?
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Unread 02-17-2013, 03:32 PM   #11
PaYj
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yes the gauges are working, thats the one thing i heard ppl say was their fuel gauge would not work along with others, mine is working even with the advance auto ckp in it, this all started when i was having a hard time starting in cold weather i did a tune up and found the distributor bearing was bad so i replaced it, it ran for three days like a champ and then lost spark
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Unread 02-17-2013, 05:09 PM   #12
715raccing
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I went through 2 junkyard pcm's .The original to the Jeep and the first junkyard replacement were both bad.Neither would pulse the coil to ground.That may be why the junkyard Jeep ended up in the junkyard.
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Unread 02-17-2013, 05:29 PM   #13
Rich93ZJ
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I know this sounds real basic but are you sure your battery is up to par. Try and swap it out with a known good battery (Don't just jump it). The electronics in these are very temperamental about getting high enough voltage and with it being 10 degrees outside it can dramatically effect the battery voltage. Its worth a shot. G/L
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Unread 02-17-2013, 09:01 PM   #14
PaYj
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battery is brand new, and i had a charger on it while doing all this to make sure while is cranking it didnt get low
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Unread 02-17-2013, 09:07 PM   #15
ZeeJay1997
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Did you check the spark at the coil or plug wire? I'm wondering if the rotor is broken...
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