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Unread 06-10-2013, 08:45 AM   #1
xxtegra
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2002 KJ Liberty 
 
Join Date: Oct 2012
Location: crousetown, novascotia
Posts: 18
computer burned up ?? with pic

ok was having some problems few mths ago here is link http://www.jeepforum.com/forum/f28/p.../#post14315272

now just getting time to work on this again .it all started with one coil not getting power then 2,3,4 ect,tried a new computer and it worked on same 5 cylinders as when the problem started .so today i decided to take the old computer apart and this is what i find

jeep1.jpg  
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Unread 06-10-2013, 08:47 AM   #2
xxtegra
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2002 KJ Liberty 
 
Join Date: Oct 2012
Location: crousetown, novascotia
Posts: 18
what would cause this ? cut wires in the harness?
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Unread 06-11-2013, 06:00 AM   #3
Billwill
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2002 KJ Liberty 
 
Join Date: Jul 2007
Location: South Africa
Posts: 901
Quote:
Originally Posted by xxtegra View Post
what would cause this ? cut wires in the harness?

Yeah something shorting out to chassis somewhere probably.
I did see a link somewhere of a possible short somewhere near the alternator but cannot find the link now...the short could be anywhere and you need to trace it before frying another PCM.

It is possible you have a bad coil pack for instance which blows that part of the circuit....now you swap that bad coil pack with one in a different position and the bad coil pack blows another section of the PCM and so on.

It can be difficult to physically trace wires fraying to ground as the harness tends to take a long round about route...you will need to remove the battery, disconnect the PCM, measure all leads coming out of the PCM for continuity to ground using a good Multmeter.

You can get the circuit diagrams for your 2002 KJ here.....included in the 2002 KJ Service Manual.

http://www.colorado4wheel.com/manuals/Jeep/KJ


There is no circuit diagram for the PCM itself but if you physically trace the blown components in the PCM to nearby PCM connector pins you can check where those connector pins go to in the circuit diagram Connector Pin-out Table....should narrow down your path to take ie. coil pack, injector etc.

Note that as stated before in your link, the coil packs all get +12 volts on one side while the other sides are grounded in turn by the PCM so if one of those leads goes to ground intermittantly the coil pack could burn out which in turn could cause that circuit to draw too much power and burn out the relevant Transistor/SCR in the PCM.
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Unread 06-11-2013, 06:58 AM   #4
streetglideok
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2005 KJ Liberty 
 
Join Date: Jul 2011
Location: Colorado Springs, Colorado
Posts: 2,294
Just a word of correction, the V6 has coil on plug, not coil packs, different systems. Regardless, you have battery power on one side of the coil connector, and a pcm controlled ground on the other. With multiple transistors cooked, you have a problem that needs fixed before you put another pcm in. Make sure you check the powers and grounds to the pcm, and also check for shorts to ground in the wiring to the ignition coils from the pcm. Follow thru what Billwill said, as that is a sound starting point. If you have the old ignition coils, check their resistance on the primary side, the two pins where the connector plugs into, then also one pin at a time against the secondary side of the coil...where the spark comes out.
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