hesitation and backfire 4100
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HT4100 4.1, 4.5, 4.9 Discussion, hesitation and backfire 4100 in Cadillac Engine Technical Discussion; I took the car to local mechanic for car had slight miss and hesitation during acceleration but at higher speed ...
  1. #1
    grantjr's Avatar
    grantjr is offline Cadillac Owners Member
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    hesitation and backfire 4100

    I took the car to local mechanic for car had slight miss and hesitation during acceleration but at higher speed cant feel hesitation or miss.he told me it seems to be valves or something internal. he also stated the plugs and wires were perfect.Drove her today and as i was pulling off or hesitating off the was a slight backfire.I love this car the body and interior is mint.So before i invest in refurb engine i need advice on what to do. The mechanic is reputable but he could be wrong,boy i hope so.....WHAT DO I DO NEXT????????

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    carnut is offline Cadillac Owners Master
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    Re: hesitation and backfire 4100

    You could be lucky and have a weak fuel pump. Verify fuel pump pressure. Usually they backfire from worn out camshafts and the reason they wear out is coolant leaks internally and washes off the oil from the cam lobe. Sometimes you can see evidence under the oil filler cap. If its milky light tan I would suspect failed intake gaskets and failed camshaft.

  4. #3
    The Ape Man's Avatar
    The Ape Man is offline Cadillac Owners Connoisseur
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    Re: hesitation and backfire 4100

    What he said.

  5. #4
    Bigblacktruck is offline Cadillac Owners Member
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    Re: hesitation and backfire 4100

    My '83 Coupe Deville is doing the same thing. The oil and antifreeze look fine. Is there ANYTHING else to try before writing it off as a bad cam?

  6. #5
    aeronca36606 is offline Cadillac Owners Enthusiast
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    Re: hesitation and backfire 4100

    Pull the valve covers and look at the valve lift on each rocker assembly. If any look bad, Remove the intake manifold and any bad lobes will be evident. (Usually associated with a build up of sludge by the bad lobe) When Antifreeze mixes with engine oil it causes the oil to break down and form sludge. This can cause distributor drive gear failure (been there done that) to the point of completely stripping the gear. It can also block off the oil flow to a camshaft lobe. (usually on the front or rear lobes under the intake manifold water passages) and in extreme cases it can block the flow of oil back into the block from the heads. This can starve the engine of oil causing burnt main and rod bearings. It can also cause the main bearing saddles to crack and brake. It can also cause enough carbon build up to form on the valve stems to cause them to stick. (Been there too) There is actually a TSB bulletin covering this that recommends the valves be replaced with a new designed valve with an under cut stem to allow build up without causing valve sticking. I managed to clean a couple of sticking intake valves in one of my engines by removing the intake manifold and cleaning the stems working through the intake ports.
    This engine had also stripped the distributor gear and had a few weak cam lobes. I was able to correct most of the problems and did drive the car for a while but finally found it best to replace the engine.
    BTW if your 4100 is a FWD version, I know where there are a couple of old stock rebuilt units available cheap. Got mine for $300 plus shipping.

  7. #6
    VEGASELDO91 is offline Cadillac Owners Fanatic
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    How is your ignition cap?

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    Bigblacktruck is offline Cadillac Owners Member
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    Re: hesitation and backfire 4100

    Thanks aeronca. I'm going to print that and keep it with me when I tear into this thing.

    I just bought this car on the 24th of this month. Thought for sure it would just be a timing issue. You'd think I'd have learned by now, but I'm a sucker.


    Quote Originally Posted by VEGASELDO91 View Post
    How is your ignition cap?
    I replaced the cap, rotor, and coil. They were the originals from '83. The pickup coil tested fine, as did the Ignition Control Module. I'm sure the plugs and wires could stand to be replaced, but I hesitate to blame all of these issues on bad plugs/wires. As deep in denial as I am, it sure fails all the tests for bad cam lobes. I just really didn't want another project right now! LOL

  9. #8
    carnut is offline Cadillac Owners Master
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    Re: hesitation and backfire 4100

    When the cam fails, it will backfire thru the throttle body underhood. Back in the day, I would power brake the engine just above idle and if it had a series of backfires evenly spaced from the throttle body, 90% of the time the cam was gone.

  10. #9
    jzchen is offline Cadillac Owners Fanatic
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    Re: hesitation and backfire 4100

    Quote Originally Posted by Bigblacktruck View Post
    Thanks aeronca. I'm going to print that and keep it with me when I tear into this thing.

    I just bought this car on the 24th of this month. Thought for sure it would just be a timing issue. You'd think I'd have learned by now, but I'm a sucker.




    I replaced the cap, rotor, and coil. They were the originals from '83. The pickup coil tested fine, as did the Ignition Control Module. I'm sure the plugs and wires could stand to be replaced, but I hesitate to blame all of these issues on bad plugs/wires. As deep in denial as I am, it sure fails all the tests for bad cam lobes. I just really didn't want another project right now! LOL
    Plugs and wires did wonders for my car. Why not try before this other nightmarish stuff!

  11. #10
    carnut is offline Cadillac Owners Master
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    Re: hesitation and backfire 4100

    I disagree. Pulling the driver side valve cover is quicker than plug wire replacement and should verify flat cam or not. Once the cover is off, start the car and watch every rocker arm, they should all pivot at the same angle. In most cases the underside of the cover will have a light brown milky oil/coolant residue as well.

  12. #11
    cadillac_al is online now Cadillac Owners Connoisseur
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    Re: hesitation and backfire 4100

    I guess some of us have different meaning of backfire in different parts of the country. Around here backfire is usually a loud bang like a gunshot out the tailpipe. We call bad cam noises "popping" through the carb or tb. Is your backfire out the tailpipe or through the tb? If it's out the tailpipe then it probably is an ignition problem. My 92 Deville went 196k miles on the original plug wires but I never recommend anyone keeping their wires for life; only if it is running perfectly, and yours is not so the obvious stuff should be ruled out..

  13. #12
    83CADMAN's Avatar
    83CADMAN is offline Cadillac Owners Fanatic
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    Re: hesitation and backfire 4100

    It was flat cam lobe for my 83 Eldo, front, #1 cyl. Could hardly FEEL, much less see any lift at #1 when I pulled the valve cover.
    Already started tearing in to it. Parts gona run bout 300 bucks, thatís for cam, lifters, timing gears with chain and gaskets.
    While the radiator is removed I think Iíll send it out to be checked over.

  14. #13
    carnut is offline Cadillac Owners Master
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    Re: hesitation and backfire 4100

    When I did the intake gaskets on my 1st 84 Eldo, I replaced the tin valve covers with the cast aluminum ones from an 85. The O ring gasket in the cover provided a better permanent seal.

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