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PostPosted: Wed Jul 11, 2012 9:30 am 
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Joined: Sun Apr 01, 2012 10:22 pm
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Year and Trim: 1991 Bonneville LE
had old coil and icm tested and were friedordered replacements from autozone and connected them to the car and now the rpms are higher and erratic. I have pre and retarded ignition and the engine stall frequently. the service engine soon light is off and and the only trouble code that flashes is 12 3 times and then nothing. I guess that means the emmissions system is working and somehow the problem is back in the coil and ignition module. spark plugs are great and wires are brand new. the fuses and relays and maxi fuses are okay fuel pump pressure is at the correct psi. Is it possible to wire the 2 modules so that the engine is poss working 180 degrees off? is it poss to hook the coil up backwards.

when I took the old ones in to be tested i didn't know it was two seperate modules bolted together as gasket compound had been used to glue the 2 together and I never saw the old wiring connected. I downloaded a diagram to reconnect but I am not sure it is right as it says to check the old wiring and note how it is connected as there could be differences. What do I do now?

thanks in advance for your reply.


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PostPosted: Wed Jul 11, 2012 1:01 pm 
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Joined: Tue Aug 25, 2009 8:32 pm
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Location: Dearborn, MI
Year and Trim: 1993 SSEi
1986 LeSabre Limited
1984 GMC K2500
Don't set too much store by the OBD-1's ability to recognize and set a SES light, unless you left a sensor unplugged.

I always recommend removing the type-1 ICM (single large coil package on the ICM) and installing the type-2 ICM (3 separate coil packs on the ICM) from a junkyard. I can never remember which year to take the ICM from though...

How was it running that prompted you to replace the ICM? The tester for the ICM module has been known to be inaccurate at best. It might be that the ICM was never a problem, or that the new one is broken out of the box.

Is it misfiring, or just idling high? What do you mean by "pre and retarded ignition"? Tell us how it idles/runs from a cold start until it's warmed up, then how it drives.

For the 3.8 (and many other engines):
The engine has 3 pairs of cylinders. Each pair (1/4, 2/5, 3/6) are always on the same stroke (up or down) in the same position, but on opposite side of the cycle; ie one on the compression stroke and one on exhaust stroke but both in the same position and same direction of travel reletive to the head. Each pair of cylinders has a single coil, and both plugs fire at the same time, but the one on the exhaust stroke is wasted - hence waste spark distribution. It's impossible to hook the wires up backwards on a single coil. Even the type one coil pack is really three seperate coils but they are molded into a single 'package' and are not individually servicable.
If you hooked up wires incorrectly to the wrong coil you would have a misfire, not high/inconsistant idle, and the engine would shake. If you hooked them up really backwards, the starter nose could break off and the engine wouldn't run...

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PostPosted: Wed Jul 11, 2012 5:28 pm 
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Year and Trim: 1991 Bonneville LE
When i say pre and retarded ignition I mean that the gas try to detonate in Cylinder before compression stroke is done and in the exhaust pipe. I replaced the icm because there was a loud pop then I couldnt start the car anymore it would turn over but that was it fuel was not even being pumped out of the tank to the injectors. when I had the components tested one of the wires on the icm had burned through the car would crank but no fuel or spark before that the car ran like a top except fuel economy was 10 mpg in town and 18 on highway now I seem to be getting 15 in town and 30 freeway.

It idles smooth at about 1500 -2000 then drops to 750 and 400 stalls and when it is started when cold it starts right up idles okay and the tach needle bounces between 750 and 2500 occassionally. when it warms up it can idle rough and then stall repeatedly before it finally runs for a period with no probs. when the rpms vary the timing is affected and is advanced and delayed & that causes the backfires . When you say shake do you mean vibration or like the spin cycle is unbalanced in a washing machine?


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PostPosted: Wed Jul 11, 2012 6:36 pm 
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Joined: Tue Aug 25, 2009 8:32 pm
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Location: Dearborn, MI
Year and Trim: 1993 SSEi
1986 LeSabre Limited
1984 GMC K2500
I think we can rule out misfire. And it would be a vibration almost exactly like an unbalanced washing machine.

First things to check, is for a plugged/partially plugged catalytic convertor or collapsed exhaust pipe.

Next check the mass airflow sensor by unplugging it and starting it cold to see if it makes the problem go away (it won't run very smooth, but won't die either). It's a pain to remove, but it should be cleaned. It is best removed with an impact driver and a properly sized phillips bit. I replaced mine with internal hex machine screws (I think they were 4mm x 1.25) to prevent further stripping of the heads. Use mass airflow sensor cleaner on it and brush softly with a small soft horsehair acid brush.

Inspect the crank sensor and the wiring harness between the crank sensor and ICM. Look for broken wires, the vanes on the harmonic balancer hitting the sensor, etc.

Check the coolant temp sensor. If you have an ohm meter, you could hook it up and put in boiling water (2.5K @ 80 degrees, 200 @ 212 degrees)

Also check for vacuum leaks (deteriorated hoses, broken lines, etc.)

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WeeEE-ROAAAAR-PSHhht! Ba-dub-badubbadub-badub-ba-dub
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'86 Buick LeSabre Limited - dead-ish Pics, accident
'93 Pontiac Bonneville SSEi - Custom engineered performance! Build thread
'89 Buick LeSabre Limited
'87 Buick LeSabre T-type
'93 Bonneville SE
'97 Buick LeSabre
'84 GMC Sierra Classic


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