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1991 Cadillac Deville Runs Rough Weak Spark HELP

8558 Views 11 Replies 7 Participants Last post by  steelybill
Hi, I have a 91 Caddie Coupe with 102K miles. It was running real rough when I got it. We did plus, wires, cap. and rotor. A little better but still stumbling. I also replace the coil and ignition module. Still no difference. What am I missing. All I do know is the spark coming out of the disturbutor is real weak
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Apparently it wasn't the distributer. Any codes?
There are no codes to be found
With a meter you could check for full 12 volts coming into the distributor at the connector. Low voltage there could make for a weak spark. Just a suggestion......
the control unit in the Distributor. maybe that is on it's last legs and hasn't yet failed completely. The unit is fairly easy to remove and most auto parts stores will check it for you for free. The unit is notorious for heat related failure. If it dies completely, you will get no spark at all.
As steelybill noted, check the supply voltage to the distributor. After that you might look for a vacuum leak.
He mentioned that he replaced the module. I assumed he meant the one in the distributor.
If you feel like gambling, a bad MAP sensor can make it run pretty bad and sometimes takes a while to set a code. They are $25-50.
He mentioned that he replaced the module. I assumed he meant the one in the distributor.
if that's the case, then I don't see how the spark can be the cause of the problem. All those new parts for the ignition circuit should have eliminated that. "Weak" spark?
would be defined as not enough to start the car, but the car starts and runs so apparently it is getting plenty enough "spark". I vote for the MAP like Al says. Gotta be fuel related.
I went through 2 sets of plug wires before I found a set that really worked. First set was the cheap Advance ones (big mistake). Then I got AC Delcos. Those only lasted about 4 months before they started to fail (arcing to metal).

I then got the large diameter Accel wires and they have been fine so far. My local repair shop said he has had the best experience with the high end NAPA wires (Belden I think) and the large Accels.
Yeah, it could be the wires. We tend to look for complicated things sometimes, when it's something simple.:shhh:

The connectors on late model stuff don't seem to have corroded pins and/or spades like the old stuff, but it still could be a culprit.
I fixed the cruise on mine by cleaning all the connectors related to it. Under-hood fuses can be a problem also.
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