Engine surging - no DTC's
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RWD 19xx-1984 DeVille and Fleetwood,
1985-1996 Fleetwood and Brougham Forum Discussion, Engine surging - no DTC's in Past Cadillac Vehicle Discussion; Hey all. I've been taking the kiddos around for Spring Break to different places (first time I've taken the Brougham ...
  1. #1
    TopherS is offline Cadillac Owners Fanatic
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    Engine surging - no DTC's

    Hey all. I've been taking the kiddos around for Spring Break to different places (first time I've taken the Brougham out of town since I bought it in September). We've had some car trouble that I'm hoping to get some help with.

    The problem is with engine power and surging. Monday, while going through the mountains to the coast, we did not have a problem with it...I was able to keep 55-65mph uphill to keep up with traffic, no problem. But coming back that afternoon, things started off fine, but then, going up hill, the Brougham started surging...very rhythmically...sort of a VROOM, vroom, vroom, vroom, VROOM, vroom, vroom, vroom, ...etc. The whole car would speed up/slow down in this "rhythm" about once per second or two...rocked the car forward and back as it did it (as in front-to-back...not side-to-side). The car stayed right near 50mph the whole time with the pedal floored and would slow down very significantly if I let up on the pedal at all (letting up on the gas pedal would be like completely taking my foot off the pedal...no power at all). Once I was either on a relatively flat road or going downhill, it would clear up.

    Then yesterday, out on a different highway, I noticed the same thing...except that it would act up even on slight hills or under steady, brisk acceleration (even on flat roads). It appears that if I don't accelerate too briskly, it won't act up under acceleration, but if I am brisk in my acceleration, it will surge.

    All of this seems to happen around 50mph.

    This morning, I went to the garage and pulled the trouble codes...nothing but a '12'.

    I did a tune up about 2 months ago...new wires, plugs, distributor cap/rotor, fuel filter, air filter, had the car timed, etc. After that tune up, the car has run beautifully...still does...except when this surging sets in. My MPG did not seem improved much by the tune up. Before my tune up, my MPG (mostly, about 80% or so, city driving) was at 11mpg. Now it's 12mpg since the tune up. I'm not sure what other info would help.

    I am due to drive this car to/in/around Colorado/Utah and back home in June, so this is something that will need to be fixed by then. With my mostly city driving, I don't have to live with this problem too much on a day-to-day basis...but there's a lot of hills/mountains between Portland and Colorado Springs.

    Your help is greatly appreciated. Thanks in advance.


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  3. #2
    sven914 is offline Cadillac Owners Connoisseur
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    Re: Engine surging - no DTC's

    I would check the vacuum lines, to make sure there aren't any that have started to dry rot. Check to make sure the THERMAC (the round thing on the end of the air cleaner) is opening and closing; it should be closed with the engine cold and open as it warms up. Also, check the connector on the distributor, to see if it's plugged in all the way.

  4. #3
    SafariOne is offline Cadillac Owners Fanatic
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    Re: Engine surging - no DTC's

    Thermac will rarely cause surge, you are most likely looking at the EFE valve being faulty or the MAP sensor or map sensor circuit.

  5. #4
    TopherS is offline Cadillac Owners Fanatic
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    Re: Engine surging - no DTC's

    Today, the problem became significantly worse. I now can't go over 35 mph without problems and even have some problems below 35 mph...including stalling.

    I have already checked the EFE Valve and it appears to be functioning. I was able to move the lever back/forth and when cold, it is in one position and I observed it move to the other position after the car was idling for about 2 minutes.

    I still need to check for worn vacuum hoses...but I can say that the car idles smoothly and when not stumbling/stalling, accelerates smoothly without any apparent misses. I was under the impression that a vacuum leak would cause problems at all times...therefore, I hadn't initially considered a vacuum leak as the cause.

    I'm not sure how to check the MAP sensor/circuit.

    I also noticed a small puddle of antifreeze on the garage floor on the center/driver's side (new symptom).

    I'm afraid that this problem is going to turn my car into a 4,000 lb paperweight.

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