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Discussion Starter · #1 ·
As you can see from last four posts about my 97 Z28 with only 35K, I have been going nuts with Code 300 and running rich on Bank 1 with code 132 high voltage O2 sensor bank1. I think the Code 132 is the result of too much unburnt fuel in the manifold as a result of the misfires.

I nave done EVERTHING that can be done to address misfires: new plugs, wires, injectors, OPTI spark, coil, manifold vacuum test 21, compression tests on Bank 1 where the misfires are traced to, ( at least 120 to 140 on a cold motor- would be almost impossible to do a proper compression test because of the confines and considering the low mileage, lack of oil on the spark plugs and no signs of head gasket or valve issues, I don't think its a mechanical issue. Further, because they are multi-cylinder, random misfires it's highly unlikely to have multiple bad cylinders on such a low mileage motor. I checked for vacuum and exhaust leaks, inspected the bank one cat for blockage, replaced the Bank 1 o2 Sensor and checked the wires running from the ECM to sensors, fuel pressure checked out 45 lbs., Pulled valve cover off and checked for broken valve springs.

The car starts OK, bit after it warms up it runs rich with -36 fuel trim on bank1, misfires usually code 300 but some times 303, 305 and 307 (all Bank1). I am beginning to think the ECM might be bad. After reading a few websites regarding ECMs, it appears that code 300 ( random multi-cylinder misfires) are a common symptom of a failing ECM. I always thought ECM failure was binary they are either bad or good but it appears they can partially fail. The ECM visually appears to be clean and doesn't smell like burnt wires.

One other thing that is leading me to think it's the ECU is that these problems started last Spring when I took the car out of winter storage. Unfortunately the battery float has been knocked off several times and in two instances I had to replace the battery because it froze solid in there subzero Minnesota winters. I used a high output jump starter to get car started after long periods being dead as a door nail. I think I might have reversed the polarity once when jumping, saw a spark but the starting unit is supposed to be protected for that.

These are the givens:

The car runs rich on Bank1, misfires and backfires solely on Bank1
All ignition components on Bank1 from the Opti back to the plugs and wires are new
The engine has good intake vacuum and cylinder compression
There is fuel pressure and the injectors are new.
Yet something is causing multiple cylinder to multiply misfire on bank1
Through the process of elimination it can only be ignition or timing.

Has anyone out there had any experience with a bad ECM ? I don' t want to spend anymore $$$ or time on this project and would appreciate any knowledgeable inputs.

Thank You!!
 

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While reversing polarity won't hurt most stuff on your car, the computer is very sensitive to things like extreme overvoltage and reversed polarity.

While I won't say the computer is the problem, it could be. Buying a new or rebuilt computer is a good sized investment. So I'd hate to recommend buying one and it not solving your problem.
 

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Discussion Starter · #3 ·
I tried switching front O2 sensors and still the same old song. PO 132 high voltage S1B1
Still runs rich with misfires on Bank1. As I said I was able to check compression on 3 and 7 which sometime misfire and they had at least 120 -140 on a stone cold motor.

Now the car wont idle until it warms up and still gives a flat line .8 with no wave form on B1S1 At times PO 300 random multi cylinder misfires and sometimes PO 303, 305 and 307 always Bank One. MY thoughts are the misfires are filling the manifold with unburnt fuel that's driving the O2 Sensor to the max which in turn results in negative fuel trim.

The question is why am I getting multiple multi-cylinder misfires ONLY on Bank One? The rich condition and brand new injectors basically rule out fuel issues. The new OPTI, plug wires and plugs on Bank One would rule out most common ignition issues.

The compression tests, manifold vacuum check @21, removal of the Bank 1 valve cover and inspection for broken valve springs, lack of oil on the spark plugs, no head gasket symptoms and only 35k on the motor would rule out mechanical issues.

I took the computer out yesterday and opened it and visually examined the circuits boards, i didn't see any obvious anomalies like a burned up capacitor or an obvious broken solder connection. That doesn't mean the computer is not the culprit it would be just be good indication if you see obvious degradation or damage.

Any inputs would be greatly appreciated.
 

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I have a ‘96 PCM from my WS6 Trans Am that I deleted Vats off of, it worked when I took it out,
If you need it, let me know. It’s collecting dust, rather save another F body and help a brother out. I am looking for some rear compartment panels(the ones the rear speakers are housed in) I could really use those. Perhaps you can help me out and I’ll do the same for you.
Let me know.
Ben Smith
 
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