please help - 1995 bonneville needs new PCM? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 10-10-2009, 03:41 PM   #1
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Default please help - 1995 bonneville needs new PCM?

Hi guys,

I've been trying to fix my GF'* '95 bonneville for months. I just cant figure it out.

The thing sometimes starts right up, and drives fine.

On another day it will take 2-3 cranks to start and run for awhile, but then will sputter and sometimes even just shut right off (like you turned it off). It will crank right back up tho.

Other days it takes for ever just to start and sputters and runs like crap. It shuts right off while driving.


I've looked at the Battery cables, MAF, the EGR, hose leaks, wires/plugs good, changed the O2, changed the crank sensor and other sensors, changed TPS, etc, etc.... the list goes on.

From what i've read it seems it could be the PCM gone crazy? I've read that the 94/95 PCM'* are notorious for going haywire on these cars. I've heard that the PCM is located behind the air intake and also under the passenger side dash. Where is it and whats involved in changing it out? Is it a PITA? I'm guessing remove neg battery, etc..

Thanks for any inputs.
This thing is driving me NUTS!

-Glade
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Old 10-10-2009, 04:22 PM   #2
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Try local salvage yards. Those PCMs are getting harder to find. You could also try Ebay. I do believe that year is under the glove box. There'* a chip you remove from you current PCM, and put that in the new PCM, and it should be fine.
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Old 10-10-2009, 04:25 PM   #3
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thanks dan. i found it. any special tips in removal?

they have it at autozone/advance auto for about $100. its not called pcm with them.........they call it computer only.
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Old 10-10-2009, 05:59 PM   #4
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Disconnect the battery (negative) and that'* about it, just transfer the chip. $100 is about right for price.
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Old 10-10-2009, 08:41 PM   #5
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Whoa....whats the trick to getting that sucker out?

It looked simple enough, yet i cannot get it out of its plastic (sleeve) that seems to hold it in its vertical position. I tried taking the glove compartment out, but there'* just ducting and braces behind it. The only way to get the PCM out seems to be from the bottom.

What am i missing?? Is there a "trick" to popping that sucker free?

Thanks in advance,
Glade
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Old 10-10-2009, 08:45 PM   #6
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That I don't know. Toddster might know how. I know billboost does, but he'* not on during the weekends.
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Old 10-11-2009, 02:42 AM   #7
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Quote:
Originally Posted by gladesteen View Post
Whoa....whats the trick to getting that sucker out?

It looked simple enough, yet i cannot get it out of its plastic (sleeve) that seems to hold it in its vertical position. I tried taking the glove compartment out, but there'* just ducting and braces behind it. The only way to get the PCM out seems to be from the bottom.

What am i missing?? Is there a "trick" to popping that sucker free?

Thanks in advance,
Glade

It'* hard because it is too simple to believe. After you get the footcover off under the dash, the PCM is clipped onto the plastic frame on the footwall. the clips are part of the frame. Lay under it and look around as to what clips are holding. I forget if there are one on each side and maybe one in the middle. it takes no force to pry them back, so you can slide the PCM down and out from the frame.

Even putting it up is easy. You just start it from underneath, sliding it up in the guides of the tray. There are clips on the frame at the top which you can't see. They will catch, and then you slide and snap it into the frame.

I am on my 3rd PCM for the '95. The first two were preceded by many hours of trying to fix a problem existing only in the mind of the computer. The last one, I got a camshift position sensor error. This is a favorite of the '95, and a really bad one because the message actually means there is something wrong somewhere in your entire ignition circuit. Put in a fresh PCM, and the DTC code was gone, never to return.

So you have to have two pCMs at a time. One in play and one as backup. (I get them for $20/pc at the pull-it yard). If i get an odd message, the first thing I do is put in the new computer.

There is a blue e-Prom inside the boxes. Be sure to swap in your original one. That has your id number. In my state, you can't pass inspection if your car has one VIN# and the computer has another.
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Old 10-11-2009, 10:24 AM   #8
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Charlie,

Thanks for the input. I had to give up yesterday because i was getting frustrated again.
I will tackle again today.

I went through and checked/replaced EVERY air elbow on that thing yesterday and cleaned every electrical connector i could find. I pulled/cleaned/replaced the PCM connections also.

The car seems to be running better.

It still has a stutter, which i believe must be caused by the PCM.

Here is what its doing now. Starts up fine, runs a little rough then settles down. After awhile it just "hiccups" and the gauges go bezerk/ck eng light on/and almost stalls (this lasts 1 sec) then it "catches" itself and goes back to idle.

Does that sound like PCM to you?

I hate throwing money at this car.

Thanks again,
Glade
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Old 10-11-2009, 02:32 PM   #9
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update:

I pulled the PCM out and cleaned the motherboard up. It was nasty on the backside. I ended up removing the whole board and then used alcohol and q-tips to clean it up.

Put it all back together and it ran fine for awhile. I took it for a drive to get more electrical cleaner and while i was at autozone it started doing that "freak out" thing where the engine/lights/alarm chime for 1 second happens. After it stumbled and came back i let it sit idling. The RPM'* were searching going up and down. Sounds like TPS to me, but its already been changed out. Guess i will clean up the TPS and IAC again.....see what happens.

If this still keeps happening, i guess ill bite the bullet and go get a new PCM.


-Glade
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Old 10-11-2009, 02:54 PM   #10
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I don't believe the problem is your TPS, if that were the problem you would stumble at the same point(*). And the IAC would not effect the RPM readings.
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