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Unread 02-15-2015, 04:56 PM   #1
67dartgt
Registered User
1998 XJ Cherokee 
 
Join Date: Jun 2011
Location: carpinteria, ca.
Posts: 15
My '98 Xj sport 4x4 will not pass smog ( California ). Though my tail pipe is clean (emissions wise), I had no active monitors thus failing smog. At first I thought the Computer was hung up because I had problems with the idle position sensor but, no check engine light. So, I erased all drive cycles with my obd2, planning on re-setting the drive cycles/driving. ( I had nothing to loose) After a couple tanks of gas and several hundred miles, I decided to scan my computer once again once again. I had found that the oxygen sensors, fuel, catalysts, misfire, and evap had run their drive cycles. I was almost there! When I scanned the car the next day, I had lost my O2 sensors, evap, and catalyst. What the hell?? So, yesterday, I drove the crap out of it, and had completed all drive cycles but the evap. Again excited! I went back outside and scanned the car, all drive cycles were gone!! Am I loosing power to the pcm? Some how, my drive cycles are getting erased when I turn off my ignition. Has anyone heard of this? Is my igniting switch killing power to the pcm? My radio is not losing power. My battery is new. Thoughts? Suggestions? Anything?


Last edited by 67dartgt; 02-15-2015 at 07:23 PM..
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Unread 02-15-2015, 07:21 PM   #2
67dartgt
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1998 XJ Cherokee 
 
Join Date: Jun 2011
Location: carpinteria, ca.
Posts: 15
Scans from two different days:
image-1720135359.jpg

image-2247316724.jpg

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Unread 02-15-2015, 11:37 PM   #3
pshivers
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2008 KK Liberty 
 
Join Date: Sep 2012
Location: Westerville, OH
Posts: 174
I've attached some diagrams and drawings for you to check out.

You have one of a few things going on. Either you're dropping out the one fused power feed to the computer, one of two grounds or your PCM memory is shot. I believe if you had a power or a ground dropping out and resetting your computer, your jeep would die while driving. I think the memory or some internal connection in the PCM might be the more likely choice.
pcm-connections.jpg  
File Type: pdf PCM Connectors.pdf (30.9 KB, 10 views)
File Type: pdf PCM power.pdf (40.0 KB, 9 views)
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Unread 02-21-2015, 06:12 AM   #4
ZeeJay1997
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1997 ZJ 
 
Join Date: Dec 2008
Location: Sweet Home, Alabama
Posts: 7,354
the fused battery power is more suspect in this case.

could be a problem at the pcm connector or PDC. you can get on pin 22 with a meter and move things around in/under the PDC and see if the voltage is stable.

If this checks out, you could be looking at replacement PCM.
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Unread 02-22-2015, 12:40 PM   #5
67dartgt
Registered User
1998 XJ Cherokee 
 
Join Date: Jun 2011
Location: carpinteria, ca.
Posts: 15
I'm leaning more towards PCM a replacement. It seems as soon as I approach completing my drive cycles, the PCM starts to purge data. This has happened about five times. I'm thinking that the PCM memory is compromised, only capable of holding small amounts of memory. The car can hold memory for several days but once it starts approaching completing its drive cycles is when the data gets deleted. My next question is if I buy a new PCM does it have to be flashed by the dealer or do most PCM's come with programs installed? May be a PCM reflash from the dealer?
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Unread 02-24-2015, 08:10 PM   #6
ZeeJay1997
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1997 ZJ 
 
Join Date: Dec 2008
Location: Sweet Home, Alabama
Posts: 7,354
no flash is required. it should be plug n play.
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