'94 Buick Regal - Intermittent cut out while driving

Folks,

My 1994 Buick Regal has developed a problem that is driving me
crazy!

First, details on car: 133K miles, 3800 V-6 (Code "L"), 4T65E
transaxle, California emissions (has dual O2 sensors). Has that weird
1994/95 ECM system that is OBD1 electrical interface (12-pin ALDL
connector) but puts out OBDII DTCs. Recent maintenance includes new
battery and smog test for license plate renewal (no stored DTC codes
in ECM per the smog tech).

What is happening is that the engine will just quit while running.
Happens when throttle not depressed (decelleration) with or without
brake pedal pressed, during both straight ahead running and turns.
Never has happened when car is standing still at idle. When this
happens the Check Engine light comes on (but not before stall, just
afterwards) AND the Air Bag light also comes on and flashes (does the
same power-on self test routine as when the car is first turned on).

Whole routine is highly intermittent - car can go for 3 weeks or
more between episodes or do it 6 times in one trip home from the
office (as happened yesterday). Also, engine does not hesitate or buck
before shutoff (the action one would expect if it where a fuel
starvation problem) - acts just like you turned off the ignition
switch. All other electrical devices such as the radio and HVAC blower
do not quit working at any time. Once you put the car in neutral the
engine will restart immediately without hesitation.

I'm thinking intermittent loss of electrical power to the Ignition
Module and ECM - traced schematic and the ignition module, ECM and SIR
controller are fed from same path through ignition switch (fuses for
ignition and ECM fed from common line from ign. switch to Underhood
Center #1 and air bag feed from same contact on ign. switch via feed
to fuse box in glove box). Checked the fuses, connectors etc. on this
path but could find no obvious problems. I've also checked the ECM &
ignition grounds under the ignition module bracket - they are solid
(I've had problems with those on my old Olds 9. I've discounted (for
now) crank sensor, ignition module and such because of air bag light
coming on.

Any tips from the group would be appreciated. I'm real leary of
taking the Regal to the dealer's service dept. - I've worked on cars
and electronics long enough (40+ years) to understand that
troubleshooting intermittent electrical problems can be a real bitch
and also that too many mechanics will just shotgun it (throw parts at
the problem) until the problem goes away. Cannot afford to do that.

Ian, I would especially value your evaluation of the problem. From
your postings you seem to have an excellent grasp on some of the
weirder problems that afflict GM cars.

Thanks in advance for any help the newgroups can provide.

Regards,
Bill Bowen
Sacramento, CA

"William H. Bowen" wrote in message
> Any tips from the group would be appreciated. I'm real leary of
> taking the Regal to the dealer's service dept. - I've worked on cars
> and electronics long enough (40+ years) to understand that
> troubleshooting intermittent electrical problems can be a real bitch
> and also that too many mechanics will just shotgun it (throw parts at
> the problem) until the problem goes away. Cannot afford to do that.
>
> Ian, I would especially value your evaluation of the problem. From
> your postings you seem to have an excellent grasp on some of the
> weirder problems that afflict GM cars.
>
> Thanks in advance for any help the newgroups can provide.

Very true, Bill. I had an 89 Regal that did just the same, and multiple
trips
to the dealership availed nothing ("We cant fix it if it isnt acting up").
Warranty
is worth nothing if they cant fix it, right?

I have know some people to trade their cars they got so frustrated with
this sort of problem.

Ian is an excellent source of reliable information.

In my case, the Buick zone representative recognized my problem as
being an ECM which was constructed during a run using bad semiconductors.
He ordered it replaced with no further haggling, and the problem was solved.
Yours is probably something different, but I can appreciate your quandary