Need Help with timing/tune-up on 84 Cadillac Deville HT4100
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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; ...
  1. #1
    henrydean40 is offline Cadillac Owners Member
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    Need Help with timing/tune-up on 84 Cadillac Deville HT4100

    This baby has been driving like a dream...until recently. The minor issues have started to pile up.
    The concern right now: there is a pretty severe "hesitation" when I push on the gas pedal (I guess the issue could also be described as a lack of power or slow throttle response). It happens when starting from a stopped position, but also when cruising down the road and then trying to accelerate. I've replaced the fuel filter, air filter, checked/changed spark plugs/wires, changed all the fluids...and the list goes on.

    After doing quite a bit of research through some of the postings, it seems to me that I should advance the timing a bit to fix this problem. If you have any other possible suggestions, I'd LOVE to hear them. The timing currently sits at the factory setting of 10° BTDC (measured with the green connector by the distributor unhooked and the ALD jumper connected from A to B).
    The only problem is: I CAN'T FIND THE DARN DISTRIBUTOR CLAMP BOLT!!!! I've been searching and feeling my way around for days and I'm starting to lose my mind. I went and purchased a distributor wrench from NAPA for $26.50 (and that's with the discount). However, I still cannot find the bolt. There are several wires and tubes and even a bracket that are right next to distributor and in the way.

    Can anyone tell me where to find the distributor clamp bolt for this engine so that I can adjust the timing?? I can upload a picture if that will help.

    1984 Cadillac Sedan Deville HT4100.

    Thanks,
    JH

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  3. #2
    henrydean40 is offline Cadillac Owners Member
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    Re: Need Help with timing/tune-up on 84 Cadillac Deville HT4100

    I found the bolt, but there were tubes and wires and framing in the way. I was forced to purchase the exact distributor clamp wrench that was shown in the haynes manual after searching at several different places and trying several different wrenches. I ended up finding the wrench i needed at a pawn shop while looking for cheap wrenches to bend into shape....it was a lifesaver and made the job a breeze.

  4. #3
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Need Help with timing/tune-up on 84 Cadillac Deville HT4100

    Changing the timing is a band aid. Have you checked the cap contacts for excessive spark erosion. Pulled the DTC's?

  5. #4
    henrydean40 is offline Cadillac Owners Member
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    Re: Need Help with timing/tune-up on 84 Cadillac Deville HT4100

    Actually I just replaced the distributor cap and rotor with a hi performance set from Schucks (there was definitely evidence of spark erosion on the old set). This made a HUGE difference! The throttle response is much, much better, but there is still the hesitation when I push on the pedal and put the engine under load. By DTC's do you mean the error codes? If so, I have checked them... but right now everything is clear.

    Next, I plan to replace the catalytic converter with a magnaflow version, and replace the plugs with Denso Iridium plugs to see if that will help.

    I just took it to Mieneke the other day, and the tech noted that "the vehicle may have a misfire, and it exhibits low vacuum". But they need to investigat more, which means more $$$$$$....

    Could it maybe be the low vacuum??

  6. #5
    Ranger's Avatar
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    Re: Need Help with timing/tune-up on 84 Cadillac Deville HT4100

    I suppose you could have a partially clogged CAT. Especially on a car that old, but any muffler shop should be able to do a back pressure test prior to installing a new CAT to see if it is needed.

    I don't know about the vacuum claim, but you could easily put a vacuum gauge on it and check it as well as check all the vacuum connections.

  7. #6
    henrydean40 is offline Cadillac Owners Member
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    Re: Need Help with timing/tune-up on 84 Cadillac Deville HT4100

    They said that the CAT was okay, not perfect but fuctional. However, I already had the new one order so we'll see how that goes.

    I was just reaching with the vacuum comment, I'm just not sure what else would cause the car to hesitate so drastically when I push on the gas pedal. Another thought I had was to replace the throttle position sensor, but again, just reaching.

  8. #7
    Ranger's Avatar
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    Re: Need Help with timing/tune-up on 84 Cadillac Deville HT4100

    I recall our old Guru (a GM powertrain engineer) saying that a bad TPS would cause symptoms similar to a bad accelerator pump on a carbureted engine. That's what you are experiencing. That said, the TPS should set a DTC if it was bad, but then who knows. Just something to consider.

  9. #8
    ehall's Avatar
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    Re: Need Help with timing/tune-up on 84 Cadillac Deville HT4100

    A common problem on the older GMs is for the shaft on the throttle body to wear out and develop a sporadic vacuum leak at different points in the acceleration. This was the source of the unsolvable hesitation problems on my 85 a few years ago (in conjunction with sporadic service soon telltale and a couple of other problems), and I see it mentioned a lot in my current research. Ask the shop to check for vacuum leak around the shaft to diagnose.

  10. #9
    henrydean40 is offline Cadillac Owners Member
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    Re: Need Help with timing/tune-up on 84 Cadillac Deville HT4100

    Thanks for the suggestion. I located a throttle body repair kit on rockauto.com, and I was just curious if you think that might fix the problem? Or, would I likely need to replace the shaft and get a repair kit? I'm very mechanically inclined, so I'd like to get in there and check it out, but do you think this is something I should attempt myself??
    I prefer to do most all the work myself, which can be a headache sometimes , but I love to learn how it works and how to fix it....and also to save some dough.

    Thanks again for your help.


    Quote Originally Posted by ehall View Post
    A common problem on the older GMs is for the shaft on the throttle body to wear out and develop a sporadic vacuum leak at different points in the acceleration. This was the source of the unsolvable hesitation problems on my 85 a few years ago (in conjunction with sporadic service soon telltale and a couple of other problems), and I see it mentioned a lot in my current research. Ask the shop to check for vacuum leak around the shaft to diagnose.

  11. #10
    ehall's Avatar
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    Re: Need Help with timing/tune-up on 84 Cadillac Deville HT4100

    I don't know any rebuild kits that include a seal. There are some good ideas for SBC throttle bodies on the thirdgen.org forums. You should check to see if it's drawing vacuum before you try to engineer a solution.

  12. #11
    henrydean40 is offline Cadillac Owners Member
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    Re: Need Help with timing/tune-up on 84 Cadillac Deville HT4100

    The engine performance analysis stated that it exhibits low vacuum, so that means it is indeed drawing vacuum, correct? Or is there a different vacuum check that I need to do?

  13. #12
    ehall's Avatar
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    Re: Need Help with timing/tune-up on 84 Cadillac Deville HT4100

    LIGHTLY spray some carb cleaner around the part of the throttle body where the shaft comes through the side and see if the engine revs. Get a feel for it by spraying down a vacuum line first. The stuff is flammable so don't let it puddle up.

    Generally speaking hesitation happens when there is not enough fuel or spark to form full combustion. Could be low fuel, or too much air, or weak spark. I'd check fuel pressure and spark color too.

  14. #13
    raiderromo is offline Cadillac Owners Member
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    Re: Need Help with timing/tune-up on 84 Cadillac Deville HT4100

    i have an 81 cadillac eldorado barritz, that we replaced the motor with one of a 84 eldorado the ht4100. car ran great, then one day it just turned off while driving. it was hard to get it started just to make it home. since then i have been pulling my hair to figure out whats wrong with it. i replaced cap, rotor, wires, plugs, fuel pump, fuel filter, air filter, valve cover gaskets, coolant temp. sensor, one of the two map sensors that has a hose attached to it. other on only has a wiring harness attached to it. i have been to the junk yard to replace some parts & hoses that were just old. car turns on and stays on..runs better, but when i accelerate the car runs really rough, like its missing. i didnt replace the coil inside distributor, because a mechanic buddy told me the car would not start if that was bad. i also replace a sensor that mounts to the side of the throttle body..i think the throttle position sensor, it didnt have any type of adjustment. when i accelerate you can see it move. we had a carb. shop clean out the injectors inside the throttle body. he said they were a bit dirty. but car still runs very rough at acceleration, wants to shut off if i put it in gear, have to keep pumping gas to keep it on. any suggestions??? i want to take it to a mechanic, but cant keep it on. i found out through these forums, that these are a pain in the behind cars. only thing i could think about replacing would be egr valve, pcv valve, 02 sensor, and thermostat. have someone check the timing, and gear inside distributor....anyone have similar issues

  15. #14
    henrydean40 is offline Cadillac Owners Member
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    Re: Need Help with timing/tune-up on 84 Cadillac Deville HT4100

    I sprayed the throttle body shaft lightly with carb cleaner, and it seemed that the engine very slighly revved up when spraying on one of the sides. It was barely noticeable though. Should it be revving up when spraying??

    Also, When I checked the spark plugs, I compared the color to the chart in the haynes manual, and the plugs appeared to have been sparking okay. I'll be checking the fuel pressure tomorrow.

    Quote Originally Posted by ehall View Post
    LIGHTLY spray some carb cleaner around the part of the throttle body where the shaft comes through the side and see if the engine revs. Get a feel for it by spraying down a vacuum line first. The stuff is flammable so don't let it puddle up.

    Generally speaking hesitation happens when there is not enough fuel or spark to form full combustion. Could be low fuel, or too much air, or weak spark. I'd check fuel pressure and spark color too.

  16. #15
    68cadu is offline Cadillac Owners Member
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    Re: Need Help with timing/tune-up on 84 Cadillac Deville HT4100

    Hey just wondering if you ever solved the problem. I have a 84 coupe that's doing the same exact thing and it's really dangerous when merging into traffic. I did a full tune up but still doing it. Please let me know if you have figured the problem. Thank you!
    nebulosity likes this.

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