4.9 running rough after spark plug change Help!
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HT4100 4.1, 4.5, 4.9 Discussion, 4.9 running rough after spark plug change Help! in Cadillac Engine Technical Discussion; To start with I changed my spark plugs and wires today with Ac Delco Parts, Now my car idles and ...
  1. #1
    Keilyn STS is offline Cadillac Owners Member
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    4.9 running rough after spark plug change Help!

    To start with I changed my spark plugs and wires today with Ac Delco Parts, Now my car idles and accelerates rough but when im at a steady rpm it is smooth.

    I also noticed that there is a loud sound like a large vacuum leak near the back driver side of my engine.

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    drewsdeville's Avatar
    drewsdeville is offline Cadillac Owners Master
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    Re: 4.9 running rough after spark plug change Help!

    There are a number of vacuum lines back there, including the vacuum supply to the brake booster which could create quite a large leak. Track down the sound and repair the leak.

  4. #3
    the recluse is offline Cadillac Owners Connoisseur
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    Re: 4.9 running rough after spark plug change Help!

    Quote Originally Posted by drewsdeville View Post
    There are a number of vacuum lines back there, including the vacuum supply to the brake booster which could create quite a large leak. Track down the sound and repair the leak.
    Agreed. Start there. May have removed the main vacuum line in reaching the rear plugs.

  5. #4
    Keilyn STS is offline Cadillac Owners Member
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    Re: 4.9 running rough after spark plug change Help!

    ok found and fixed the vacuum leak. My car is still running rough and I dont know what to do.

  6. #5
    the recluse is offline Cadillac Owners Connoisseur
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    Re: 4.9 running rough after spark plug change Help!

    Did you pull any codes?

    The other thing you might want to do is check and make sure that all the boots are pressed firmly on the plugs and/or the plugs are tightened to the heads, just a thought...

    If it ran good before the plug change, than it is more than likely something you did/didn't do...

  7. #6
    Keilyn STS is offline Cadillac Owners Member
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    Re: 4.9 running rough after spark plug change Help!

    I have no codes, Ill double check over everything tomorrow when I get out of school

  8. #7
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    Re: 4.9 running rough after spark plug change Help!

    I had this problem when I did the plugs and wires on the neighbors Caprice. I decided to pull them all and redo the job (reset gap, reroute wires, everything), and it worked great on second try.

    In my case I am pretty sure that I had too much silicon grease on a couple of the plug tips.

  9. #8
    daniel58 is offline Cadillac Owners Fanatic
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    Re: 4.9 running rough after spark plug change Help!

    If you still have problems after checking the above, distrubutor cap, rotor, module would be good places to look/replace.

  10. #9
    Keilyn STS is offline Cadillac Owners Member
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    Re: 4.9 running rough after spark plug change Help!

    UPDATE!!!!!!!

    Car will not start now
    I went over the spark plugs and wires multiple times. and nothing
    I noticed when enine was cool it would run good but when it got to operating temp it would start running ban and begin to feel like it had no power.

    the only code im getting is a p052(history)

  11. #10
    the recluse is offline Cadillac Owners Connoisseur
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    Re: 4.9 running rough after spark plug change Help!

    Look into your ignition control module and the coil; both can be tested at your local parts house. A failing ICM will give the previous symptoms mentioned...

  12. #11
    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: 4.9 running rough after spark plug change Help!

    You need to check for spark at the plugs. You will need a friend to help with this. If there is spark then you need to check the fuel pressure. You will have to buy or borrow a gauge. Another way to check the fuel would be to dump a shot of gas down the throttle body and see if it fires. since this is the easiest i would probably try this first.

  13. #12
    Keilyn STS is offline Cadillac Owners Member
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    Re: 4.9 running rough after spark plug change Help!

    everything fixed now, needed new cap and rotor, runs like a brand new car

  14. #13
    the recluse is offline Cadillac Owners Connoisseur
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    Re: 4.9 running rough after spark plug change Help!

    Quote Originally Posted by Keilyn STS View Post
    everything fixed now, needed new cap and rotor, runs like a brand new car
    Good show....

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