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Unread 04-17-2013, 08:53 AM   #1
ZJNewbi3
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1995 ZJ 
 
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Location: Milwaukee, Wisconsin
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Replacing my PCM

I'm replacing my PCM in my 1995 5.2L V8 Limited today and was wondering if I need to flash the new computer or not? There is no sticker on my old one saying I need to and the instructions that came with the new one said "you may need to". I've been 3 weeks without my ZJ and I need this thing to run so I'm hoping for plug and play!

Also is there any re-learn process or anything else? I plan on testing the voltages on my old PCM to confirm that it is dead then disconnecting the negative terminal on the battery then pop in the new PCM reconnect the battery and start it up. If it doesn't work the thunder storms tonight will put out the flames...

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Unread 04-17-2013, 09:31 AM   #2
JohnCrabtree
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1994 ZJ 
 
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Anytime you disconnect a battery cable your electronics will reset. Which means that there will be a relearning process but that just means you start it and let it idle for a few minutes when you reconnect the battery.

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Unread 04-17-2013, 10:23 AM   #3
ZJNewbi3
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Great! does the new PCM need to be flashed though?
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Unread 04-17-2013, 12:07 PM   #4
JohnCrabtree
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Quote:
Originally Posted by ZJNewbi3
Great! does the new PCM need to be flashed though?
Sorry, i dont know the answer to that

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Unread 04-17-2013, 12:45 PM   #5
Bigdjs123
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Quote:
Originally Posted by ZJNewbi3 View Post
Great! does the new PCM need to be flashed though?
It depends on the pcm that you baught. Where did you get it?
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Unread 04-17-2013, 01:34 PM   #6
ZJNewbi3
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rock auto
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Unread 04-17-2013, 01:44 PM   #7
Bigdjs123
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If you go back to theri catalog it should say in the desription of the part if it needs flashed
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Unread 04-17-2013, 03:22 PM   #8
ZJNewbi3
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It didnt need to be...put it in today and the jeep still doesnt start...so now I have

no voltage at fuel pump
no spark
all relays work
no blown fuses
crank sensor, MAP, and TPS sensors are not getting power nor shorted
cant get CEL readings either

am I missing something here? Only thing I can think of is the PCM ground but I cant find it on my V8. Bout to give up on this thing soon.
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Unread 04-17-2013, 08:54 PM   #9
ZeeJay1997
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The grounds to the PCM are on the passenger side of the block below the head.
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Unread 04-17-2013, 09:10 PM   #10
tizzly
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I might have read of the o2 sensor causing something like this. I could be wrong, but its not hard to check the wires to see if they are melted on the exhaust
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Unread 04-17-2013, 09:27 PM   #11
ZJNewbi3
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Awesome! Where would the wires be? And there are two o2 sensors correct?
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Unread 04-17-2013, 09:44 PM   #12
tizzly
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1995 should have 1, its located in front of the cat. The wires should lead up over the transmission. Just follow the wires and look for any breaks or burns. Also look for any other wire problems. Again im not for sure its your problem but cant hurt to look. Another possibility is your grounds,.check for loose or rusty conections
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Unread 04-17-2013, 10:17 PM   #13
ZJNewbi3
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do you know where the grounds are located in a 5.2L V8 because I can only find locations for the 4.0L I6 online unless they are the same? Sorry for all the questions this is my first vehicle and I'm learning steadily. Hope this rain lets up after school tomorrow so I can actually check everything -.-
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Unread 04-17-2013, 10:36 PM   #14
tizzly
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They shoukd be the same as the 4.0. Get one of the repair manuals from pep boys or advanced auto, they're full of helpful information
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Unread 04-18-2013, 07:59 AM   #15
JS97ZJ
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If your going to spend any money on a manual, get a downloadable FSM online.
The paperback toilet paper they sell in part stores are crap. For getting wiring diagrams and other specific info you'll need the factory manual. (10-15 $)
I read some of your previous threads to get some history and you asked about an aux backup light. Did you install it? Where did you hook it up?
You could overload a circuit if it's not on it's own system and blown out a needed fuse for the rest of the vehicle.

The power source for the relays ASD, fuel pump etc. comes from the PCM (5v, 8v). Check the gnds and battery connections like Zee said and recheck all of the fuses.
Here is the PCM connector diagram so you can back probe it with a meter.
95-5.2-pcm.png  
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