Lound thump when shutting off engine, then no restart
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HT4100 4.1, 4.5, 4.9 Discussion, Lound thump when shutting off engine, then no restart in Cadillac Engine Technical Discussion; Hi, My 93 Deville is giving me some issues, It has a 4.9L When i shut it off i hear ...
  1. #1
    behind-bars is offline Cadillac Owners Connoisseur
    Automobile(s): 93 Sedan Deville 4.9L
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    Lound thump when shutting off engine, then no restart

    Hi, My 93 Deville is giving me some issues, It has a 4.9L

    When i shut it off i hear a sound like someone pounding on the door, It sounds like the speaker popping, but it happens with the radio off so I know thats not it. When i go to restart it within a few mins it makes a quiter, yet repetitive thumping sound and doesnt start right away, after several tries it finally starts up.

    After the noise on shutdown I quickly jumped out and popped the hood, I see a bit of smoke coming from around the radiator, so I may have to investigate a leak.

    But the leak doesnt seem like it would cause the noises I hear.


    Any Ideas?

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    HUF's Avatar
    HUF
    HUF is offline Cadillac Owners Connoisseur
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    Re: Lound thump when shutting off engine, then no restart

    Backfire through the intake. Start the car with open hood , have someone watching.

  4. #3
    behind-bars is offline Cadillac Owners Connoisseur
    Automobile(s): 93 Sedan Deville 4.9L
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    Re: Lound thump when shutting off engine, then no restart

    What is the best way to attack this issue? Should I try changing fluids like oil and coolant out and maybe trying to clean up the inside of the engine some. Or am i looking at replacing parts and tearing into the engine? I am looking at web posts trying to get an idea of what all could be at fault, but would appreciate any further tips from anyone. I think ill park it till its resolved.


    Unfortunately today my other 93 blew the T joint at the heater core a few miles from home, in the rain, with temps at 40. What a long walk home lol, only to have this 93 start backfiring and refusing to start as i left the parts store with the new T and some coolant. I ended up using jumper cables to loosen the hose clamps since I had no tools with me initially, dont ask me how i thought to do that, but it worked untill i got a pair of channel locks to install the new joint. Unfortunately by then it was 30 something degrees and raining. I changed it out in the middle of a dark; wet parking lot with headlights as my only source of light, only to forget the antifreeze at home. lol.

  5. #4
    HUF's Avatar
    HUF
    HUF is offline Cadillac Owners Connoisseur
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    Re: Lound thump when shutting off engine, then no restart

    Quote Originally Posted by behind-bars View Post
    What is the best way to attack this issue? Should I try changing fluids like oil and coolant out and maybe trying to clean up the inside of the engine some. Or am i looking at replacing parts and tearing into the engine? I am looking at web posts trying to get an idea of what all could be at fault, but would appreciate any further tips from anyone. I think ill park it till its resolved.

    Unfortunately today my other 93 blew the T joint at the heater core a few miles from home, in the rain, with temps at 40. What a long walk home lol, only to have this 93 start backfiring and refusing to start as i left the parts store with the new T and some coolant. I ended up using jumper cables to loosen the hose clamps since I had no tools with me initially, dont ask me how i thought to do that, but it worked untill i got a pair of channel locks to install the new joint. Unfortunately by then it was 30 something degrees and raining. I changed it out in the middle of a dark; wet parking lot with headlights as my only source of light, only to forget the antifreeze at home. lol.
    When it rains it pours... Had a heater core leaking on the toes of my female passanger in the middle of nowhere with only Swiss Army knife available toolwise. Well, it was enought to rerout the heater hoses in the egine bay to bypass the heater core. I have been keeping a nice set of tools in my trunk since...
    Back, to the thump. Could it be mechanical? Say, a bad motor mount/mounts. Do not tear down the engine before you actually know what is going on. I believe a bad FPR or leaking injectors could cause that type of backfire. Probably someone with similar experience will chime in. Again, have someone looking at the engine when it happens. A trusted girl friend is just fine. LOL

  6. #5
    behind-bars is offline Cadillac Owners Connoisseur
    Automobile(s): 93 Sedan Deville 4.9L
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    Thread Starter

    Re: Lound thump when shutting off engine, then no restart

    I dont think it would be motor mounts, could be something mechanical though. It has lived in Texas its whole life so we dont have the rust issues some places have, but I suppose they could still go bad. Ill look into FPR, etc before tearing into it. Ill also have someone looking when i start it to see if they see the source.

    I started changing the coolant out in it today since its leaking somewhere. When I popped the hood after the backfire I saw smoke near the radiator and I left a puddle in the driveway so I know its leaking external the engine. Ill try to identify the coolant leak and clean that up, and will check fpr while im at it. I will run codes to sine i forgot before. Also will check the oil to make sure it looks normal

    Thanks for the help.

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