I aquired a 1980 Grand Marquis with 113,000 miles. The engine is the 351. The car suddenly stalls while driving, after 15-20 minutes. It will idle all day. After stalling, it will start immediately back up and stall within 30 seconds. I can repeat this procedure and each time it stalls 5 seconds sooner. If left to cool, it will stall depending upon how long it cooled off. I suspect cats are old. The previous muffler was rotten but the shop said the cats looked usable. Before changing the muffler, the car stalled but after a longer driving period. I have changed the fuel pump as well. Leaving the gas cap on or off for vacuum has no effect. I also only slightly suspect hat the new fuel pump is bad. Coil? Ignition? Oh, I bought the special fluid and rented the tester for a cracked block as well and all is well. I hate to spend $700 on cats for no reason. When idling, there is exhaust coming from the tail pipe. Oh yea, changed the o2 sensor as well. 1 cat each side feed the single exhaust. Helllllp?- mark

 

If 80's have the spark control module that's what it sounds like to me. I pressure washed my '76 Granada engine compartment and had the same problem. Had to replace the module.

 

Began having this problem on my '79 Marquis, 302 engine. Bought a HEI distributor on ebay for 50 bucks. It replaces the module and coil. All you need is a 12V wire to it. Runs perfect now.