1991 lesabre chugging and stalling when run hot

Please help. 1991 Lesabre 3800 with 320,000 miles stalls and won't run good after driving 12 miles on freeway. Used scan tool due to CEL coming on after symtoms arise. Received Problem ID 2504 Trouble code 42 and coses 56 55 54 53. Replaced Fuel pump relay. Drained and flushed coolant and installed a new thermostat. Unhooked ground cable each time I did repair and symptoms still reappear along with the same codes. Searched posts and saw something like EDR and PCM could be related to codes. My scanner reads codes as follows 56= Corrositivty add col 55= ECM ADV Error. 54= Fuel pump relay. 53= Over voltage.Any ideas as sesors and controls are still expensive and I am baffled why it will run good on road test. Then performance will again decline. Scan tool is a Matco 4000. Are codes related to one thing being wrong . Thanks in advance for any help.

run it by autozone have them hook it up it's free. sounds to me like coils are getting hot. check the spark if blue there good coil if yellow not good may be coil pack problem. those 3.8 or 3800 is same thing and good engines.

Code 42 indicates that the Electronic Spark Timing (EST) signal did not change when the ECM applied bypass voltage to the ignition module. Check for faulty connections, or a faulty ignition module.

I agree with scrapper,

Check or replace the coil packs. I had similar symptoms and the coil packs check out fine when cold and ohm checked out also within specifications. After the engine was warmed up I rechecked the coil packs and found one to be defective on one side. $28 at Autozone and good as new.

Relaced the coil the ignition control module underneath it. The spark plugs and wiress. Same codes reappear as before. Could this be it need a brain box or what most call a computer (ECM)? The car will run after short disconnection of battery but will stall and have CEL flicker and tick repeatedly along with other red idiot light on the dash. Are these symptoms of a bad computer is there a test for the computer to prove that it is the problem?

Relaced the coil the ignition control module underneath it. The spark plugs and wiress. Same codes reappear as before. Could this be it need a brain box or what most call a computer (ECM)? The car will run after short disconnection of battery but will stall and have CEL flicker and tick repeatedly along with other red idiot light on the dash. Are these symptoms of a bad computer is there a test for the computer to prove that it is the problem?

you might try a new pigtail that go's to you alt. there not very much if that's not it i would say computer.

I did order a computer and will install tomorrow as I saw in other posts that it will show faulty fuel relay and is a common problem. Will post if it solves issue. Love this forumn. Couldn't do it without you guys. Thanks

Has run well since replacement of computer. Solved all issues. After installing computer you have to run it with a/c on for five minutes then for five minutes while in drive with wheels blocked then five minutes driving. Has worked thus far. Thanks

Hey i have a 91 LeSabre custom and its used to stall a bit at start idle and when acceleration, it seems a bit better now, but its still not very good, my coils arent good i think. the blue stuff leaked within it but not on the outside. but i have benn told its the fuel pump?