Weak Spark 5.2L need help - JeepForum.com
 
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post #1 of 4 Old 12-15-2012, 04:24 PM Thread Starter
LonAllen
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1994 ZJ 
 
Join Date: Aug 2004
Location: Tampa
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Weak Spark 5.2L need help

I have have found that my 94 5.2L has spark but it is really weak. I can see a yellowish spark if I use a screw driver on the coil secondary and the engine block. I get an even weaker spark out of the coil wire at the distributor. No spark at the plugs.

New cap and rotor, new spark plug wires, new Crank Position Sensor, new coil. Kolak was suggesting it might be a grounding issue. Has anyone had this problem and found a bad ground causing it? Where did you find it? cleaned grounds at the block where the battery is attached and the ground on the fender beside the battery. No luck.

Any suggestions?


Lon Allen - 94 ZJ Limited 5.2 327K miles and counting
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post #2 of 4 Old 12-15-2012, 04:31 PM
ratmonkey
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caps in the pcm or grounding to the coil.
have you checked coil resistances? a bad coil out of the box isn't unheard of.

'97 zj 5.2, some stuff, some other suff, and some things that even work sometimes.

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post #3 of 4 Old 12-16-2012, 06:43 AM Thread Starter
LonAllen
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1994 ZJ 
 
Join Date: Aug 2004
Location: Tampa
Posts: 89
Quote:
Originally Posted by ratmonkey View Post
caps in the pcm or grounding to the coil.
have you checked coil resistances? a bad coil out of the box isn't unheard of.
PCM replaced in March with one I purchased from Kolak. I thought the coil might have gone bad (Mopar part replaced in April) but no change with a new one (Mopar part).

Lon Allen - 94 ZJ Limited 5.2 327K miles and counting
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post #4 of 4 Old 01-09-2013, 11:41 AM Thread Starter
LonAllen
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Location: Tampa
Posts: 89
I tried a 3rd coil and got the same results. Because I am getting a ground pulse from the PCM to fire the coil I have to believe my Crank and Cam sensors are doing their job. After some poking around the wiring I am led to believe that the PCM is not synching the coil's primary ground enough to get the current flow necessary to build up the secondary voltage high enough. I have sent the PCM in for warranty replacement. ZJ has been out of commission for over 2 months.

Interesting to note, the clearish brown rubber sealant that covers the PCM PC board was full of gaping cracks to the point that some of the installed electrical components on the board are exposed to the open air. That can't be good.

Lon Allen - 94 ZJ Limited 5.2 327K miles and counting
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