I have a 1993 Buick Century 3300 wagon. It belongs to my sister in law, who after my brother dying 2 years ago has left me with a "Single Woman and her Car", the mechanics dread of dreads, lol. 6 weeks ago it started stalling once a week, usually upon climbing to the top of a grade like a freeway on ramp. Hence I changed the fuel filter. As time went on, it would stall for no reason. It went to once a day, then to several times a day. I've changed the injectors, wires, plugs. Bought a fuel tester and checked out the pressures for the pump and the rail vacuum thingy. All is perfect.

I switched from fuel to electrical in my quest...

I have run the tests according to the article at: https://www.gmforum.com/trouble-shooting-test-procedures-141/icm-test-299761/

I have a new crank sensor, fuel pump relay, TPS as well. The MAF checks out on the voltage and tap tests.

My ICM plug has some wires that are not used and have rubber nipples sticking out to mark that the terminal is not in use. (Marked by blue font)

P-N-M-L-K-J-H (screw) G-F-E-D-C-B-A

I'm not seeing a Cam Pos. sensor, the car has no tach, etc. Having less wires does not throw me because I know a 3.3 is not a V8 Bonneville engine.

The only difference in the color code is the G position, what would be a yellow wire is really a dark blue with white stripe. But it goes to the same pin on the crank sensor. Just for fun, I did a continuity test on all 4 CPS wires and got a beep.

The 3rd & 4th tests check the pulse voltage from the CPS.

The third test is wire G. I did get the 6.5v to zero volt alternating signal. So the 18X CKP test checked out.
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Here'* where I'm stuck...

One thing I noticed is the instructions seem to have a contradictory element. On the 4th test, 3X CPK signal test on the H wire, it says you should see 5 or 6 volt to zero volt alternating signal pulse as you rotate the crank. I do; 6.5v also.

But if the answer was yes it says the ICM is bad and to replace it. That is confusing to me. It says that I SHOULD see 5-6V'* then says it means the ICM is bad. You can only have yes or no and both answers require changing a "bad" thing. So after you change the "bad" thing, wouldn't you still get a yes or no answer?

My question is, do I change the ICM if I am seeing the pulse signal? I would think the test should result exactly as the 18X test.

Me thinks there is a typo. I'm in a quandary over it. I need this car out of my driveway. lol
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The car still starts, runs for 3-30 seconds and shuts down. I can't get it to the end of the driveway :/

Oh, and I went to a DIY junk yard and bought a used ECU with exact numbers and letters on the paper label. I mean there was not one letter or number difference. It was from the identical year car w/3300 V6, save it was a sedan not a wagon. When I cranked the motor, the engine stalled the moment I let go of the key like an old ballast resistor gone bad. I reinstalled the old computer and we're back to ground zero with my stalling symptoms of 3-30 seconds running, then kaput! I would love to get the car to a mechanic to have it tested. I would like to finish all the tests I can do myself before forking out money I really don't have to have a shop scan it. I've already got $400 into this problem.

Thank you for your help

Chet

I have a write up on the ICM test here, https://www.gmforum.com/showthread.php?t=299761 Just to make sure, check the battery cables to make sure they are tight and clean. A loose connection will cause the car to stall.

Yes, that'* the article I pasted the URL to in my post. In paragraph 3 I cite thread 299761. Can you please advise as to the question I asked regarding the conflict in the 3x CPK test, step 5? I need to know which is correct, is the ICM bad, or is the CPS bad?

Side post'* are known for trouble, however I have removed the plastic collar and I clean the terminals and spray with Napa Red Batt Protector. The terminals are nice and tight & corrosion free.

If you have a single, then the sensor is good and the ICM is bad. If you have no single, the sensor is bad.

Please forgive my over analyzing mind. lol I'm just thinking okay, I have a pulse, so I change the ICM and then what? I do the test again to check everything out and the pulse is not there, so that means the CPS is bad?

If yes means part 1 is bad and no means part 2 is bad... at what point is both parts 1 & 2 okay??

Now you know why my teachers went to happy hour after right after school.

I will change the ICM and get back to you... like in a couple hours.

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If the car runs without any problems, both parts are OK.

It wasn't a couple hours... It took 2 days because I had to wait for a check to clear.

So tonight I put on a new, out of the box, BWD ICM. Start the engine and it stalls in 3 seconds. Restart the engine and it stalls in 15 seconds. We're back to square one. :/

I'm taking it to get it scanned. Mom popped loose a credit card with a little room on it.

To be continued...

Well okay. What can I test next? I think all that'* left is the main computer; ECM? How do I test a computer?

It'* driving me to drink

Have you tested the fuel pressure?

When the car stalls, will it start right back up?

At the most basic level, an engine needs air, spark, fuel and compression in order to run. You said you tested for fuel pressure, but did you test when the engine won't start? Put a noid light (you can make one with a 12 V bulb) on each injector to see if they are firing or not. If none of the injectors are firing, the problem could very well be the ECM. This might sound silly, but smell the ECM. Does it smell like burning electronics? Check for spark on each plug when the engine won't start.

Try to determine if this is a fuel or spark issue. I know you tested fuel pressure, but as stated above, test it when the engine won't start.

Are we sure this is not a security system issue? Different cars have different reactions to a VATS error. Check the internet to see what you car does when VATS detects a problem. The symptoms may very well match what you are experiencing.

Have you scanned for DTC'*?

VATS = vehicle anti theft system
DTC = diagnostic trouble codes read from the OBD port