1983 Cadillac Seville HT-4100 Vacuum Leak?
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HT4100 4.1, 4.5, 4.9 Discussion, 1983 Cadillac Seville HT-4100 Vacuum Leak? in Cadillac Engine Technical Discussion; Hi everyone i was researching some about my Cadillac Seville i have and came across your site and thought some ...
  1. #1
    hellya2011 is offline Cadillac Owners Member
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    Unhappy 1983 Cadillac Seville HT-4100 Vacuum Leak?

    Hi everyone i was researching some about my Cadillac Seville i have and came across your site and thought some of you on here with more knowledge on the engine than me could help me out. I have been a proud owner of a 1983 Cadillac Seville for a couple months now, but i have ran into a problem which i believe to be a vacuum leak.

    I have the standard gas engine ht-4100 4.1L engine. Sometimes whenever i start the car up, it will run smooth, but then it will start to run rough. It will act like the engine is reving up, then act like the engine is about to stall or die, then rev back up, the act like it's dieing, you get the picture. Then whenever i try to drive up a hill, i will start to climb the hill at 45 mph, then it will drop down to 25 mph before i reach the top with the petal to the floor. Also sometimes on normal flat roads, i'm lucky to get it up past 45 mph sometimes not even that, more like 40 mph.

    there has also been a few times where i park the car, then get out for maybe an hour or so, get pack in, the engine starts, rev up, rev down, like before, then die. Then i have to pump the petal some and hope it starts back up for me. I have also had it where i reverse out of a parking space then the engine die in the middle of the lane. I'm assuming it is a vacuum leak somewhere. Most of the hoses don't seem to be in terrible condition but you can tell there is some age on it.

    I opened the hood of the car, trying to find a hose that was rotted, i took the cover of the air breather, and got down the the trotter body. One of the hoses toward the back (looking from the front of the car, had a split in the end. The hose goes from the left silver cover on the engine to the air breather. Could this be my vacuum leak? and how in the heck do you get it off, i tried but couldn't get it to budge :/ Also when idle, if i put the petal to the floor, the engine almost dies instead of the rpm going up.

    Then as i took the metal cylinder shape tube off the throttle body, i found dry rotted remains of a gasket which is completely done for. Could this play a part in the leak, and if so what is the name for it? Any help is much appreciated.

    P.S. on a side note... i have a belt that is whining pretty bad. I've noticed that the heater goes cold when it whines and doesn't blow as hard... any idea which belt it is? ;/

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  3. #2
    84 Eldo TC is offline Cadillac Owners Member
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    Re: 1983 Cadillac Seville HT-4100 Vacuum Leak?

    A couple of things to check out/replace as necessary:

    1. Your vacuum leak sounds like the hose that connects the pcv valve to the air cleaner. I would replace that hose and the pcv valve too.(The hose should be available at your auto parts store in a dorman catalog)
    2. You didn't state how many miles your car has but if it still has the orignal catalytic converter, and some decent miles, 80k or higher, it is probably plugged up and would make acceleration very difficult and also cause stalling.
    3. EGR valve could be sluggish or non functioning and operation should be checked.

    Hope that helps, let us know what you find out.

  4. #3
    Duane Hayes is offline Cadillac Owners Member
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    Re: 1983 Cadillac Seville HT-4100 Vacuum Leak?

    There is a idle control device that could be bad. A vacuum leak large enough to cause the problems you describe would have to be huge. To remove any rubber hose that's stuck firm, cut it off with a razor blade and install a new one. You could have a bad throttle body gasket, somethings come apart there. If you don't have a factory shop manual, you should have one to go through the trouble codes, I suspect you'll have a bunch of them.. Is your Service Soon and or Service Now light's on? If you have a noisy belt you need to adjust it, or replace it, or find out where the noise is coming from, if not a belt. The heater changing output with a whine would suggest a bad alternator, or seriously loose belt, the heater shouldn't go cold though. There's a lot of things to check with your problems, but this might be a start, good luck. Duane

  5. #4
    hellya2011 is offline Cadillac Owners Member
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    Re: 1983 Cadillac Seville HT-4100 Vacuum Leak?

    thanks for the replies, i'll start to check out some of the problems that you mentioned. The cars has 78,000+ original miles on it. Yes the service soon light is on sometimes, and when the car fails to start the service now light comes on. I tried to check the codes from the air control thing, but all it gave me was a -1.8.8, then 22, then 52, then 7.0 or something which means its finished i think

  6. #5
    carnut is offline Cadillac Owners Master
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    Re: 1983 Cadillac Seville HT-4100 Vacuum Leak?

    You need to replace the fuel filter 1st then perform a fuel pressure test. A vacuum leak on a fuel injected car will cause a higher idle, not a rough idle. The gasket on the throttle body around the air cleaner base is simply a dust shield, many are missing with no ill affects. This engine tends to develop a loose smog pump belt which will cause the alternator belt to slip and eventually weaken the battery. The belt is tightened from underneath the car! Any muffler/ exhaust shop can verify a plugged cat. converter. If the fuel pressure is weak, an idle surge can occur. The almost dying can be the idle speed motor working to raise the engine speed back up which is a normal function if the fuel pressure is weak or the converter's plugged.

  7. #6
    hellya2011 is offline Cadillac Owners Member
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    Re: 1983 Cadillac Seville HT-4100 Vacuum Leak?

    Ok so i finally got the hose off, and i REALLY NEED HELP NOW.... WHERE DO I BUY A REPLACEMENT?

    None of the GM delearships around me sell anything for my car anymore... if anyone knows an online website that has it and is trustworthy i'll buy it online, or if anyone else knows how to get a replacement hose let me know.... the part that goes around the inside of the engine cover thing snapped and no longer will sit in there snug so im basically with out a hose . here are some pics of what i mean

    img0351bl.jpg
    img0354ag.jpg

    I spayed some WD40 around that hose to see if that was the leak for sure, and the engine started to rev up when i did that, so im almost 100% positive that is my leak
    and here is that gasket i was talking about earlier

    img0349zo.jpg

    EDIT:
    ok so i bought i PCV Valve Gommet & PCV elbow and it seemed to fit like a glove where the old hose went so tomorrow i'll add a hose and see how it works

  8. #7
    carnut is offline Cadillac Owners Master
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    Re: 1983 Cadillac Seville HT-4100 Vacuum Leak?

    That hose is the fresh air breather hose. It being off or loose will not affect engine idle or drive ability. I've driven mine a whole day with that hose off the air filter by accident with no drive ability issues. It simply allows the engine to exhale into the air cleaner assembly. As long as you get a hose that is oil resistant from the valve cover to the air cleaner it will work. Heater hose will not. The gasket on the throttle body to the spacer is simply a dust shield. You might try a carb gasket of the correct diameter. It being off or torn will not affect how the car runs. When you sprayed WD 40 it entered the valve cover hole which would account for the idle rising. That hose is not a source of a vacuum leak. I dont believe you have a vacuum leak at all. I think you have either weak fuel pressure, plugged fuel filter or a plugged cat. converter.

  9. #8
    hellya2011 is offline Cadillac Owners Member
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    Re: 1983 Cadillac Seville HT-4100 Vacuum Leak?

    well as far as the vacuum leak is concerned... i added a new hose on the "fresh air breather hose" and now im hearing a loud hiss i know wasn't there before it is around the thing the second hose goes to (not sure what is called though)

    also does anyone know how to get a pre-formed fresh air breather hose? i can seem to find one, i have a hose on it right now, but i'd like to have the proper hose on it

  10. #9
    carnut is offline Cadillac Owners Master
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    Re: 1983 Cadillac Seville HT-4100 Vacuum Leak?

    The second hose on that side funnels air from the smog pump diverter valve back into the air cleaner once the engine reaches temperature or on deceleration. That breather hose was used on any 4100 engine that was used on a 82 thru 85 Seville, Eldo Coupe or Sedan DeVille or Fleetwood rear wheel drive. Because you've never listed the area where you live, I wouldn't know where to send it after I pull it off a wreck. Have you tested the fuel pressure or had the cat. converter checked yet?

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    hellya2011 is offline Cadillac Owners Member
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    Re: 1983 Cadillac Seville HT-4100 Vacuum Leak?

    this is what i currently have as an replacement for the s-shape hose... just a temp fix though

    img0360cf.jpg

    this is a smaller hose/ line that came off after i started my car after putting the temp fix (above) on my car. I put it back on pretty quickly but when i did i noticed it is falling apart also i guess im needing to get it fixed soon. When i put it back on the engine made a fluttering sound, but after driving it some today that sound stopped so im not sure why it did that.

    44367311.jpg

    and this is where i am hearing a loud hiss sound from (as far as i can tell it is coming from here

    34658829.jpg

    i could give you the area where i live through an email or personal message or something but how much would you charge to send that hose?
    And no, i haven't checked the Cat. Converted, fuel filter, or fuel pressure yet. I dont know off hand where to take it around me to get it checked, i know a lot of places will run a generic diagnostics on the car for $100

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    creeker is offline Cadillac Owners Connoisseur
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    Re: 1983 Cadillac Seville HT-4100 Vacuum Leak?

    Put rockauto.com on your favorites list, it's a good reference for parts.

  13. #12
    carnut is offline Cadillac Owners Master
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    Re: 1983 Cadillac Seville HT-4100 Vacuum Leak?

    The "hiss sound" is probably the diverter valve on the smog pump directing air into the air cleaner. The temp. hose for the breather looks OK for now. List your location in your profile, not your address but at least the State in which you live! I say again, neither of these hoses will affect how your car runs. Any established auto repair shop can do a fuel pressure test in about a half hour. Most muffler shops can check your cat. converter for free.

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    hellya2011 is offline Cadillac Owners Member
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    Re: 1983 Cadillac Seville HT-4100 Vacuum Leak?

    Quote Originally Posted by creeker View Post
    Put rockauto.com on your favorites list, it's a good reference for parts.
    thank you so much for the website... i have found so many parts on there they i eventually need to get! thanks very much! ;D

  15. #14
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    83CADMAN is offline Cadillac Owners Fanatic
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    Re: 1983 Cadillac Seville HT-4100 Vacuum Leak?

    Quote Originally Posted by Duane Hayes View Post
    There is a idle control device that could be bad. A vacuum leak large enough to cause the problems you describe would have to be huge. To remove any rubber hose that's stuck firm, cut it off with a razor blade and install a new one. You could have a bad throttle body gasket, somethings come apart there. If you don't have a factory shop manual, you should have one to go through the trouble codes, I suspect you'll have a bunch of them.. Is your Service Soon and or Service Now light's on? If you have a noisy belt you need to adjust it, or replace it, or find out where the noise is coming from, if not a belt. The heater changing output with a whine would suggest a bad alternator, or seriously loose belt, the heater shouldn't go cold though. There's a lot of things to check with your problems, but this might be a start, good luck. Duane
    Idle speed adjustment is my bet.
    hellya2011 did you fix it?
    Duane and carnut are giving you solid advise, listen to them or you could be chaseing your tail and spend a lot of cash on parts you dont need.
    Man that hose, cutting it off the valve cover in hindsight was a mistake. Its a breather hose and dosn't use a PCV. A little black silicon at the cracks would have fixed the problem.
    These cars have an AIR PUMP and a VACUME PUMP so the engine surgeing you discribe is caused by something else. Like...pluged fuel filter, Idle speed adjustment. The operation of the engine is controled by computer not vacume like cars of old.
    carnut has posted several times the procedure for adjusting the idle speed.
    Also before spending any cash I would recomend doing a power brake test to see if any back firing occurs. If so you got cam and lifter problems. Then you gota make some hard decisions.
    I had to replace the cam and lifters in my own 83 Eldo HT4100 last winter.
    Good luck.

  16. #15
    cadillac_al is online now Cadillac Owners Connoisseur
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    Re: 1983 Cadillac Seville HT-4100 Vacuum Leak?

    It sounds like a clogged catalytic to me since it only goes 25 up hill and 45 on level ground. You should check the fuel pressure first though.

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