please help - 1995 bonneville needs new PCM? - Page 2 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 10-11-2009, 07:11 PM   #11
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Quote:
Originally Posted by gladesteen View Post
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
Glade....

You have mounted a brute force attack of parts, money, and time at this problem. And that is truly admirable. But let'* step back for a moment and look at this from a problem solving standpoint.

I'm assuming you can't get the code from the check engine light? If so, it is likely because the '95 is an OBD hybrid. You need a scantool which has an OBDII ('96 and later) connector, but can read OBDI ('95 and older) data.

We're skrewed for diagnosis without those error codes. Solely for my '95, I have the first release of the Actron CP9145 with the OBDII cable. This can pick up both OBDI and OBDII codes. The problem with it is operating data displayed for OBDII cars is way limited. It leaves out fundamental things you need to know, like charging system voltage (and KR). Later releases of it are on ebay, but are only worth it if they have widely expanded the amount of data for OBDII cars.

I'm not sure the error codes would indicate the exact source of the problem, but it would definitely give us symptoms of where and how the failure first takes place.

For sake of discussion, we'll put aside the error codes and PCM for the moment.

It is highly unlikely that an air or fuel problem would cause your dash gages to all go wacky. They would only cause it because they failed and took down the electricals and electronics. So, I have one more guess for you before the PCM.

If you are sure your charging system is good (particularly the ground cable from the battery'* positive terminal to the ground connection on the bottom of the engine block) then the dash board is screaming then you have an electrical/electronics problem outside of the charging circuit.

The usual suspect is the ground bus connection under the plastic rail covers at the foot of the door openings on the driver and front passenger side. The driver side is the most frequent culprit. The wires from front to back and back to front connect there in a bus, and the bus is connected to the metal grounding plate. Over time, water gets in there and the plate corrodes or connections do.

The plate should be sanded/ground back to bare metal and each individual connection should be pulled and sprayed with a contact cleaner.

This is not wasted time, even if it isn't the cure. With that ground conjunction, it'* not a matter of "if " it'* going to cause a bizarre problem, it'* a matter of "when".

This is my best guess without error codes. Next is the PCM. Plus with this hitting electricals/electronics, you don't know what that PCM is thinking right now, or what state it is in. Consistent in design, if you have an engine light problem... and that problem is a threat to damage the engine or tranny... the PCM accesses different programming and tables to prevent you from further damaging the car. For example, if the trans has problems shifting between 3rd gear and overdrive, the PCM eliminates overdrive from the shift pattern.

We really need those codes.

I'll check back, while I try to learn more about our fuel systems, and WTH is wrong with mine.

charlie
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Old 10-11-2009, 09:29 PM   #12
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Charlie,

Thanks for the input. I will definitely look into the bus bars on the driver/pass side and see if corrosion is causing the "freakiness".

I dont want to keep throwing $$ at this and hoping it solves it. It'* definitely beginning to go the other way.....if you know what i mean.

-Glade

EDIT:
I forgot to mention that you are 100% correct on the code reading. NOBODY, and i've tried them all, has a reader that can pull codes from this thing.........ughh. Will updating the PCM with a newer one allow codes to be pulled?

Last edited by gladesteen; 10-12-2009 at 10:11 AM. Reason: forgot to answer a question
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Old 10-11-2009, 11:08 PM   #13
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the 94 & 95 are know for the PCM flaking out if that hasn't already been mentioned.
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Old 10-12-2009, 08:37 PM   #14
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Hi guys,

Well, it didnt work out. I cleaned/torqued/sprayed every connector on the car and it still willl cut off. I did ck the grounds on both driver/pass side also. They were good.

I just took a ride w/her and this thing will actually SHUT OFF at highway speed! I'm not joking, it gives you a nice "bring, bring on the alarm" and then it just gives up. The alarm goes off several times during 30-50mph range. It is accompanied with the RPM flux and then an "almost" stall, but then it catches itself. This is the craziest thing i've ever seen.

I guess the last bet has to be the PCM. Any other ideas?

-Glade
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Old 10-20-2009, 02:09 AM   #15
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yea ive had this same problem, i have a 95 bonnie and wen my car started doin that, i went thru the same trouble spending money changing everthing.

the first thing i did was changed the oil pressure switch and ICM but i grindin the base, it ran fine for a while then it did it again.

finally i came to the conclusionthat it has to be a short in a wire harness.

check the harness goin to the ICM, crank sensor , and cam sensor. its one harness, iwould jus replace because for me to find that was a needle in a hay stack !!

good luck !
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Old 10-20-2009, 09:37 AM   #16
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The Actron 9145 is available on Amazon. It has paid for itself many times over diagnosing my 95 SSEI and 94 Park Avenue. (Both with the hybrid OBD systems) With the experience availabe on this site and a list of DTC codes you can save yourself a lot of time, money and headaches. If you decide to get one you will need to purchase the connector for your vehicle and also get the 6 ft extension cable if it does not come in the kit.
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Old 10-21-2009, 09:23 PM   #17
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Hi guys,

If you can believe this, i swapped the PCM and it ran WORSE!! I think i got a bad computer from Oreilley, so i returned and got another one from advance AP. Not installed yet.
I went over and re-checked all the grounds i could find.

Where is the ground behind the oil filter? I've heard there is a ground back there somewhere, but i cant see it for sure. I hit both in the fenders, and the two in front of the engine, and the alternator. Am i missing any?

Will update once i swap the "new" computer in this time.

-Glade
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Old 10-21-2009, 10:45 PM   #18
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WHOAA!

Ok, somethings working here.

Here is the deal. Swapped the PCM again and it fired straight up. No crazy RPM/dying/stutter.......just runs!

The bad news: It runs like this with a ck eng light showing. Even when the other pcm was in, it never showed a code. Ran like silk, then sputtered/showed code for a second and died.

This time it runs, although a little rougher, but it stays RUNNING! Only bad thing is its throwing a code. Man i wish i could have that thing pulled. This stupid PCM between OBD1 and 2 is retarded.
I guess the only way is to take to the stealership and pay $75 for the diagnostic?

THanks for all the help!
I am finally happy! Well, at least i got it running safely.

-Glade
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Old 10-21-2009, 10:57 PM   #19
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What PCM did you end up with? (where did you buy it?)
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Old 10-22-2009, 10:31 PM   #20
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Glad to see you got her running Glade. Don't know if you missed my post or not but the Actron CP9145 is still available if you would rather not pay the dealership.
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