Question about 1990 Cadillac Deville

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Deville running rough

A used car lot put in an alternator, and changrd the pcm fuse, so i bought it. i had driven it only in the daytime. when i started driving at night, turning on the headlights, the engine would surge up and down and come close to stalling out, but never does. it also runs like this when i turn on the heater or a/c.the check engine soon light has come on. i jumpered the a & b terminals of the aldl connector, and the light does not flash a it runs rough day or night.

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Have you checked the ECM codes, take it to an AutoZone or similar place and have them check, they just need to plug in a device to your computer.

you should also check the MAP sensor, the ISC, and also the connectors for both. also check EGR and EVR valves. Let me know what you find.

Also since you seem to be having power problems, you should have the timing checked.

Posted on May 22, 2008

  • Benjamin Patri
    Benjamin Patri May 27, 2008

    Were you able to fix this, if so then please give me some feedback by
    rating my solution. If you need any more help, I would be glad to
    assist you, just ask.

    thanks and Have a Great Day!


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How old is your battery?
It might not be charging properly or the other alternator might not be charging functioning properly.
I would suggest to check the alternator to see if it works by starting the car and unplug the positive side of the battery; if the engine stops, it means the alternator is not working. If the engine continues running it could be your battery not taking the charge or something else in the electrical or fuel system.

Posted on May 22, 2008

  • Jaime Hernandez May 22, 2008

    I would also suggest to check your spark plug cables for proper working conditions.


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