Need Help with timing/tune-up on 84 Cadillac Deville HT4100 - Page 2
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HT4100 4.1, 4.5, 4.9 Discussion, Need Help with timing/tune-up on 84 Cadillac Deville HT4100 in Cadillac Engine Technical Discussion; This must be a common problem. I have changed practically everything on my 83 Fleetwood coupe with only 40 thousand ...
  1. #16
    David Biarritz is offline Cadillac Owners Member
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    Re: Need Help with timing/tune-up on 84 Cadillac Deville HT4100

    This must be a common problem. I have changed practically everything on my 83 Fleetwood coupe with only 40 thousand miles on the clock. But I can't drive it.
    I haven't herd of anyone solving this problem but I will change the ECM next. Hope this will fix it.

    ----------

    This must be a common problem. I have changed practically everything on my 83 Fleetwood coupe with only 40 thousand miles on the clock. But I can't drive it.
    I haven't herd of anyone solving this problem but I will change the ECM next. Hope this will fix it.

  2. #17
    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: Need Help with timing/tune-up on 84 Cadillac Deville HT4100

    The OP had low vacuum and unknown mileage. No engine is going to run good with low vacuum. Stalling at red lights is pretty much undriveable and reminds me of my failed MAP sensor.

  3. #18
    83CADMAN's Avatar
    83CADMAN is offline Cadillac Owners Fanatic
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    Re: Need Help with timing/tune-up on 84 Cadillac Deville HT4100

    I would recommend you pull the left valve cover and check valve movement at #1. cylinder.

    The early HT4100’s because of the dissimilar metal expansion and contraction properties tend to loose their intake gasket. There is so much movement due to temp changes in the cast iron heads / manifold and the aluminum block that the stock intake gasket fails. Coolant seeps into the lifter valley causing sludge to form gumming up #1cylinder’s lifters resulting in oil starvation to the lifters. The cam lobes and lifters then become very prone to excessive wear and premature failure.
    Flat cam lobes, (very common), will have you chasing your tail and throwing bucks at everything but tring to get it to run right.

    This problem was so common GM offered thru their dealers a reseal kit, consisting of a thicker gasket and a set of special intake manifold bolts. The bolts have Bellville washers (a stack of 3 per) and a lower torque spec of 12 lbs. A lot of cars had this reseal kit installed so check your intake manifold bolts for what looks like stacked or thick washers. If your engine was retro fitted you can reuse the bolts, just remember the low torque spec.

    Believe me I feel your pain. I spent a lot of time and cash only to find a flat cam at the end of the day.
    Of course, I love my 83 Caddy, so I fixed it. New cam and lifters + a reseal kit.

  4. #19
    ELDO GUY's Avatar
    ELDO GUY is offline Cadillac Owners Fanatic
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    Re: Need Help with timing/tune-up on 84 Cadillac Deville HT4100

    Check your cat especially if is the orginal I had a 82 and 85 and both the cats eventually plugged up . car Wouldnt go over 45 to fifty on hwy and it took forever to get there . Put your hand over the rear pipe and check it at idle and see is any thing is comming ou . I bet very little.

  5. #20
    ardisorn is offline Cadillac Owners Member
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    Re: Need Help with timing/tune-up on 84 Cadillac Deville HT4100

    Yours is similar to my case. My car is a 1983 Fleetwood brougham HT4100.
    The car has been in THAILAND since new. It was an american ambassador's car here.
    Anyway, It had pritty bad hesitation. I used timing light to see how the timing change when i pull the throttle quickly. (Green connector was connected) I found something funny. The ignition timing was suddenly retarded and the engine nearly stall before the RPM increase and the timing advanced increase. It suppose to increase the timing advanced while the RPM increased.
    Anyway I pull the faulty code by press WARM and OFF buttons on Electronic climate control and hold for a few second. Then it will blink the faulty code stored in the ECM. IT came up faulty Throttle position sensor (TPS) or open circuit.
    I check the wiring harness is OK then check the TPS. and it was bad. So I replaced it and it has been running great since then.

    Hope this might help.

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