1990 cutlass supreme SL keeps dying

my uncle got our 16 yo this car w 176K miles for 200$. It was parked for a few years at his neighbors and didn’t run. He had a rebuilt transmission put in, new fuel pump, new battery and my husband and son tuned it up w/ new plugs, changed oil fuel filter and recently put a new crank shaft sensor on it. The car still dies after 5 minutes and then restarts for only a few seconds.

They are about ready to throw in the towel, but it such a great project, and actually such a sweet ride and it will be a great 1st car for our son, who has spent much of his own $ for fix up. We welcome any, many thoughts and ideas.

You don’t mention whether this is a L4 or a V6 so I will assume you have the L4. This engine uses a Integrated Distributorless Ignition System. It is going to be hard to determine if loss of spark at the plugs is the cause of the engine dying. I suspect that the IDIS unit, which is not repairable, is going to be too expensive the throw a part at but you might be able to find a salvage unit for trial.

At idle the IDIS requires a ‘sync’ pulse as well as the Crank Position Sensor signel to run. At higher rpm the PCM sends an Electronic Spark Timing pulse to the IDIS to control ignition timing. I have not found where the ‘sync’ pulse is derived but it should be from the camshaft somewhere.

Hope this helps.

thank you so much for your feedback.
the car happens to be a V6.
Not sure if that changes things or you might have different ideas?

Yes with the V6 you should be able to connect a test spark plug to see if spark is missing when the engine quits. The V6 also uses a DIS but it is not integrated into the engine cover. With the V6 there are 3 coils to fire the 6 spark plugs. The igniter is a single unit that drives the coils. Once the engine rpm gets above 400 rpm, the ECM switches the igniter to accept processed spark signel from the ECM.

There is a device that connects inline with the spark plug that indicates if there is high voltage current. So connect one up and watch it while the engine quits. So get back to us about the existence or absence of spark when the engine quits.

Thank you SO much again.
They will try again tomorrow with renewed hope!
I will let you know the outcome.I do so appreciate your help.
Have a nice evening and
Fond Regards again-

Hi there-
We checked the spark and all three coils are providing spark. No messages when checking the CEL. Car will start, but misfires and produces black exhaust.

Thank you for getting us on the right track-
They tried the coils as you reccomended and then realized they were getting no signals form the computer. They replaced the “ECM”- for 85$- and it drove until they turned it off 20 minutes later! Yay! We are dancing a jig!
Thank you again!