HT4100 stalling after startup, then running fine, no bad idle
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RWD 19xx-1984 DeVille and Fleetwood,
1985-1996 Fleetwood and Brougham Forum Discussion, HT4100 stalling after startup, then running fine, no bad idle in Past Cadillac Vehicle Discussion; When I start up my 84' Brougham, it cranks over just fine, idles normally, and fires up, but then sometimes ...
  1. #1
    mad_caddy's Avatar
    mad_caddy is offline Cadillac Owners Member
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    Question HT4100 stalling after startup, then running fine, no bad idle

    When I start up my 84' Brougham, it cranks over just fine, idles normally, and fires up, but then sometimes sputters out. It really scares me.. I have to turn the key to the off position, wait a few seconds, try again. Sometimes after that it will run just fine, sometimes it will sound like its going to run fine and sputter out again.
    I replaced my battery, alternator, and alternator belt, my AC is disconnected, and I am replacing the water pump tomorrow because I believe the bearing is bad and causes a high pitched squeal.

    This is beginning to turn into a head ache. Anyone have any ideas of what this could be? I hear about the head gaskets going bad in the HT4100s often, could that be it? Or do you think it's the distributor? Rotor? Fuel pump/filter/relay/accumulator? Bad idle air controller? Ignition coil?

    If I had the know how, the room or the tools and equipment.. I would replace the motor all together, and one day may just have this done.. I was going to say "if I had the money", but I have a feeling pretty soon here with all the money I might be dumping into this motor that I could have bought a new one :-p She is so clean, I just want to get her running smooth. One less beautiful Brougham in the junk yard parted out ya know..

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  3. #2
    j2rossit is offline Cadillac Owners Enthusiast
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    Re: HT4100 stalling after startup, then running fine, no bad idle

    I would think trying to get a fuel pressure reading would be very informative.

  4. #3
    The Ape Man's Avatar
    The Ape Man is offline Cadillac Owners Connoisseur
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    Re: HT4100 stalling after startup, then running fine, no bad idle

    Only guessing but idle speed motor or TPS could be the problem. I do not recommend throwing parts at this though. That's a one way trip to Palookaville.

    Obtain a shop manual. It has trouble trees for exactly these types of problems.

  5. #4
    carnut is offline Cadillac Owners Master
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    Re: HT4100 stalling after startup, then running fine, no bad idle

    I agree with the "Ape Man" best money spent is on the shop manual. When this car shuts off, a shaft extends out of the idle control motor anticipating a restart. Have someone shut off the car while you watch this idle motor with the air cleaner partially off. If it doesn't extend then you need to verify voltage to it and then via the service manual adjust it and the TPS to spec. Its a very simple system, 2 injectors, an idle speed motor to pivot the throttle blades and a TPS to meter the pulse width injector on time. A normal running 4100 of this era should race a little upon restart then quickly settle down to about 700 RPM in park. This shaft once extended, delays retraction if the engine is cold and waits to read coolant temp and closed loop. Once it sees either, it slowly retracts as if it were a choke on a carb'd car. That water pump change is not simple on this car!! 3 different types of fasteners, pulley puller and O rings sealing the by-pass pipe. These bolts thread into aluminum so you have great potential for problems! Not the best engine to learn auto repair on!

  6. #5
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    jayoldschool is offline GM RWD V8 addict
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    Re: HT4100 stalling after startup, then running fine, no bad idle

    A malfunctioning TPS will set the CEL.

  7. #6
    carnut is offline Cadillac Owners Master
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    Re: HT4100 stalling after startup, then running fine, no bad idle

    I agree! In my experience TPS adjustments are rare except when replaced. On the other hand, idle speed control motors are misadjusted quite often from mechanics, owners and other unfamiliar people. They think its simply a set screw type of adjustment. Also after 20 some years of it operating, they do fail.

  8. #7
    mad_caddy's Avatar
    mad_caddy is offline Cadillac Owners Member
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    Re: HT4100 stalling after startup, then running fine, no bad idle

    As always, huge thanks for the informative posts. Hopefully I can keep this car on the road another 30 years.

  9. #8
    The Ape Man's Avatar
    The Ape Man is offline Cadillac Owners Connoisseur
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    Re: HT4100 stalling after startup, then running fine, no bad idle

    Quote Originally Posted by jayoldschool View Post
    A malfunctioning TPS will set the CEL.
    Good point. In this case it probably would. Sometimes they have a dirty spot like an old analog volume control and they don't malfunction long enough to throw a code.

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