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Thread: Engine Stutters when A/C is turned on.

  1. #1
    Member Oliver Holler's Avatar
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    Location:  South Carolina

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    Engine Stutters when A/C is turned on.

    More specifically, engine bucks and sputters when the A/C is turned on -and I try to accelerate.
    Turn A/C off, and all is fine.
    Now that warm weather is upon us, this crazy phenomenon rears it's ugly head...
    Who's got the answer? (or at least some company for this misery.)
    Thanks!
    Oliver

  2. #2
    Senior Member Bitsyncmaster's Avatar
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    Does your voltage drop when you run the AC? Do you still run stock ignition?
    Dave M vin 03572
    http://dm-eng.weebly.com/

  3. #3
    Administrator Ron's Avatar
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    Ignition first came to mind for me too...

    Next would be a vacuum leak. You might plug the source and see if it goes away. Diagram HERE.

    The AC works OK and the engine is strong otherwise?

  4. #4
    Owner since 2007 Farrar's Avatar
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    Compressor clutch beginning to fail?
    DeLorean status: It's complicated.

  5. #5
    Senior Member Rich's Avatar
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    Quote Originally Posted by Bitsyncmaster View Post
    Does your voltage drop when you run the AC?
    First guess is same as Dave’s. See if the fuel pump +/- voltage stays high when the AC/rad fans kick in. I’d run a pair of small test wires fm the pos/neg sides of the pump up to a good voltmeter in the cabin, then go for a test drive. See if the stumbling goes with an intermittent low voltage condition at the pump.

    Small wires are easily snaked out past the hood and past a door seal.

    Shouldn’t take long to rule this in or out. Better would be testing fuel pressure but that’s harder to do.
    March '81, 5-speed, black interior

  6. #6
    Senior Member mr_maxime's Avatar
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    While not specific to the delorean, I just had this problem with my protege. One of the ignition coils went bad and was shorting to the engine under the excess load from the AC. Listen for zaps and check your spark plug wires to see if they're shorting to the engine.

  7. #7
    Senior Member
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    if its voltage drop to the pump then that would be from the cooling fans pulling power. what about unplugging the fans to test if the issue goes away. not saying the fans are bad but that would remove considerable system voltage draw. if the problem goes away then you will know more about what's going on.

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  8. #8
    Member Oliver Holler's Avatar
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    Thank you for all the suggestions!
    Haven't found the problem yet, but the symptoms have changed. A/C on or off, it doesn't matter. Still sputtering and almost won't move forward sometimes.
    Grrr.
    O.

  9. #9
    Member
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    Quote Originally Posted by Oliver Holler View Post
    More specifically, engine bucks and sputters when the A/C is turned on -and I try to accelerate.
    Turn A/C off, and all is fine.
    Now that warm weather is upon us, this crazy phenomenon rears it's ugly head...
    Who's got the answer? (or at least some company for this misery.)
    Thanks!
    Oliver
    I had a similar issue with my engine bucking and sputtering under load late last year after cleaning my VOD. I replaced vacuum lines and a good bit of the ignition system before a friend suggested I try different plugs. I was certain that wouldn't solve anything b/c I had just replaced them the month before. Sure enough the problem went away and upon inspection I found a hairline crack in the ceramic of one plug. I'm not sure if it had been dropped or over-torqued, but apparently even the tiniest crack will cause a plug to fire erratically under load. My A/C has always caused a significant voltage drop when the fans kick in, but this happened in the fall when I wouldn't have been using the A/C so I'm not sure whether that would have made the problem more apparent. I have a new set of fans that I've been putting off installing which will hopefully resolve the voltage drops - I'll let you know if that improves things.

  10. #10
    Senior Member DMC5180's Avatar
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    Engine Stutters when A/C is turned on.

    Oliver,

    When was the last time the the ignition system was overhauled?

    Do you have the New Fuel pump module setup?

    What is your current fuel level?




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