4.9L '92 Knocking...or missing, help!
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HT4100 4.1, 4.5, 4.9 Discussion, 4.9L '92 Knocking...or missing, help! in Cadillac Engine Technical Discussion; http://www.cadillacforums.com/forums...ad.php?t=31714 I have a thread up in the Deville forum, but you guys here seem to know most about the ...
  1. #1
    Mahalaleel is offline Cadillac Owners Fanatic
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    4.9L '92 Knocking...or missing, help!

    http://www.cadillacforums.com/forums...ad.php?t=31714

    I have a thread up in the Deville forum, but you guys here seem to know most about the engine, will someone please try to help me?

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    91TexasSeville's Avatar
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    Re: 4.9L '92 Knocking...or missing, help!

    Quote Originally Posted by Mahalaleel
    http://www.cadillacforums.com/forums...ad.php?t=31714

    I have a thread up in the Deville forum, but you guys here seem to know most about the engine, will someone please try to help me?
    I have read your prior posts and the many replies.
    Let us forget for a moment about the knocking issue and focus on the misfire.

    Do this first!

    Remove the air cleaner assembly and snorkel. Look down inside the throttle body with the blades fully opened. If there is any, I mean any, carbon build-up on the bottom side of the throttle blades or inside the two tubes sticking up from the bottom of the intake manifold, thoroughly clean these items first. Take care not to scratch the walls of the throttle body or the blades. Use of carb cleaner and a spent toothbrush is normally sufficient for cleaning the throttle body and underside of blades. A coathanger is sufficient to clean the EGR tubes sticking up from the manifold. After the cleaning process, replace the snorkel and aircleaner assembly. Disconnect the battery negative cable for approximately 30 seconds. This will tell the idle speed control to relearn and correct for the cleaning process.

    If the cleaning process does not help, repost here!

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    Mahalaleel is offline Cadillac Owners Fanatic
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    Re: 4.9L '92 Knocking...or missing, help!

    I didn't see this post earlier, just to revive this, I'll be re-looking, and maybe trying this tomorrow, but I may need more help, because I have never taken anything but oil out of an engine.

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    Mahalaleel is offline Cadillac Owners Fanatic
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    Re: 4.9L '92 Knocking...or missing, help!

    I was going to do this tonight, but I got home too late, so now I'll just ask some questions for when I do do it. How do I get the throttle blades to stay all the way open, safely? And what are the "EGR tubes"... Like I said, I've never done anything but change my own oil, add oil, check tranny fluid, change that, and add coolant and wiper fluid. Stuff anybody can do if they have half a brain.

    Also, is there anything I could use in the place of carb cleaner, because I don't have any :drinker:disappoin. That I know of...

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    Re: 4.9L '92 Knocking...or missing, help!

    I had my son sit in the car and just hold his foot on the accelerator. Go to Wal Mart, O' Reilley's, AutoZone wherever and tell them you need a can of carb cleaner and they will fix you up and is less than $5. Also, I used a brush from a .410 gun cleaning kit to clean the tubes.

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    Mahalaleel is offline Cadillac Owners Fanatic
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    Re: 4.9L '92 Knocking...or missing, help!

    Well, I went in there, and it is VERY dirty. But I don't have any carb cleaner. Is there something I could use instead? I have a toothbrush currently VERY covered in black stuff...what should I rinse it in? Household things? Rubbing alcohol...? Water?

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    Mahalaleel is offline Cadillac Owners Fanatic
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    Re: 4.9L '92 Knocking...or missing, help!

    I found some carb cleaner, and got a lot out of there, but I'm sure there's more. Any simple way to remove the whole thing?

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    Mahalaleel is offline Cadillac Owners Fanatic
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    Re: 4.9L '92 Knocking...or missing, help!

    Well, I cleaned them out as much as I could given the time I had, and drove around. My mileage seemed to improve, but it's too soon to tell. It was also much more responsive... If there IS a way to get the whole carb/throttle body setup off, I could clean it much more thoroughly, and I'm sure it would help a lot.

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    Re: 4.9L '92 Knocking...or missing, help!

    Quote Originally Posted by Mahalaleel
    Well, I cleaned them out as much as I could given the time I had, and drove around. My mileage seemed to improve, but it's too soon to tell. It was also much more responsive... If there IS a way to get the whole carb/throttle body setup off, I could clean it much more thoroughly, and I'm sure it would help a lot.
    Yes, the throttle body does come off, but it is really not necessary to remove it. If you insist on removing the throttle body, you will need to replace the gasket between the throttle body and intake. Be sure to disconnect the negative battery cable BEFORE the cleaning. The cleaning can be done with the throttle body still on the car (recommended). After the cleaning process of both the throttle body and EGR tubes (those two little pipes sticking up from the base of the intake), ensure that the throttle blade bottom is clean and does not bind or stick when closed or fully open. Reconnect the negative battery cable. You will be amazed at the improvement! Plan on doing this once a year, more often if it was really dirty to begin with.

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    Mahalaleel is offline Cadillac Owners Fanatic
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    Re: 4.9L '92 Knocking...or missing, help!

    Rhanks a bunch. and by rhanks...i mean thanks :PThe main problem is that I can't reach into the EGR tubes, so I can't get all the carbon out. Is there a simple way to remove the throttle body? or any more ideas?

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    Re: 4.9L '92 Knocking...or missing, help!

    Quote Originally Posted by Mahalaleel
    ....The main problem is that I can't reach into the EGR tubes, so I can't get all the carbon out.............any more ideas?
    Do as tulsadeville stated.
    Quote Originally Posted by tulsadeville
    ......I used a brush from a .410 gun cleaning kit to clean the tubes.
    Have been using a gun barell cleaner kit myself for quite a while. Get the one with the different size brushes. Can find them almost anywhere. Comes with an extended handle and the brushes are the perfect size.

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    Mahalaleel is offline Cadillac Owners Fanatic
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    Re: 4.9L '92 Knocking...or missing, help!

    How stiff of brush should I use?I don't think anything soft would get it out. I couldn't get some of it out with the hanger, it was so solid.

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    Re: 4.9L '92 Knocking...or missing, help!

    Quote Originally Posted by Mahalaleel
    How stiff of brush should I use?I don't think anything soft would get it out. I couldn't get some of it out with the hanger, it was so solid.
    Wow Man.
    Check out the gun barrell cleaners.
    Brushes are perfect size.
    If the crap is crusty then use the carb cleaner as sugested as well. Spray it in and spray it on the brush. Maybe let it sit for abit and soak. It will dissolve and eventually break down.

    Dont think your gonna get much more info than already posted.
    Dont know myself personally, but if that dont work then maybe there's something else going on?
    No idea what it could be?
    But far as it goes it should clean off?

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    Mahalaleel is offline Cadillac Owners Fanatic
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    Re: 4.9L '92 Knocking...or missing, help!

    Alrighty, so I successfully cleaned the tb's and the egr tubes, and now i'm getting 16 mpg instead of 12 oh joy! But, the knocking/missing still occurs at 50-60 on low throttle. Also, the misfire when rev'ed still occurs. Big WHUMP every little bit.

    Any other ideas?

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    Murphyg's Avatar
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    Re: 4.9L '92 Knocking...or missing, help!

    Should start with all the plugs instead of just 2. Should also change the wires if they havent been done in a while. A new cap and rotor wouldnt hurt either.

    And if some of your injectors are shot like you were told, then that sure isnt going to help.
    Could try some injector cleaner.

    Know its hard to do, but you should be searching for someone who is reliable and can give you an honest diagnosis. You could have a hand full of different problems; or maybe just one or 2 that are sending bad signals elsewhere that is making it difficult to pinpoint.

    Something here might help
    http://www.cadillacforums.com/forums...ight=injectors

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