Chrysler Repair: 2.5L V-6: Injector control code,PCM/wiring/injector?, chrysler cirrus, 1998 chrysler cirrus

Question
Roland,

A week or 2 ago I asked you about an injector (#4 to be specific) shorting.  The problem was eventually traced it to the PCM, and I had it replaced.  The problem went away for a couple of days, before happening again today.  Shortly after starting my car, the car started running roughly and the CEL came on.  Stopping to check the codes, I got P0204 and P0304.  I checked the resistance of injector 4 and found it to be 15.6 ohms.  Checking the resistance between the control and ground wire at the injector connector, it was found to be very low (I don't remember the resistance exactly).  This is the same problem I had 2 weeks ago, and that was determined to be the PCM.  Pin 16 (I believe the control pin to injector 4 is pin 16) was grounded.  I replaced the unit and now it is happening again.  My question is: what could cause the PCM to fail like this again?  I do not have my Haynes manual in front of me, so I don't have the electrical schematic.  The car is a 1998 Chrysler Cirrus 2.5L V6 if that helps.  Thank you.

Aleks

Answer
Hi Aleks,
The injector shows a resistance in the proper range. The #4 injector control wire (light blue/brown) is on pin 16 of the pcm. The dark green/orange wire at the injector should show a steady 12v when the engine is running, and the control wire should oscillate between 12v and ground but you won't be able to see that with a voltmeter, but rather by an oscilloscope. My suspicion would be that there is a flaky connection of one of those two wires, injector 1 pin to pcm pin 6 and injector pin 2 to pcm pin 16. It could either be an intermittent 'open' or an intermittent short to ground, so check for both possiblities with the plugs removed at both ends and also shake the harness while making the measurements. I doubt it is the pcm.
Roland
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