4.9 and spark knock
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HT4100 4.1, 4.5, 4.9 Discussion, 4.9 and spark knock in Cadillac Engine Technical Discussion; does anyone know much about spark knock on the 4.9? ive had it for the longest time now.......
  1. #1
    Brizzal's Avatar
    Brizzal is offline Cadillac Owners Enthusiast
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    4.9 and spark knock

    does anyone know much about spark knock on the 4.9? ive had it for the longest time now....

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    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: 4.9 and spark knock

    Is the EGR system clean? Do you think it could be running hot? I run regular fuel in mine and it never knocks. Maybe I'm losing power and the computer is retarding the timeing but she never knocks and has plenty of pep.

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    awadecki is offline Cadillac Owners Enthusiast
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    Re: 4.9 and spark knock

    The computer won't retard the timing on 4.9s, there is no knock sensor. Cadillac al, your timing is probably conservatively set.

    Brizzal, your EGR valve is probably sticking closed. Push up on the underside of the diaphram and see if it moves. If it doesn't, you'll need to replace the valve.

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    Re: 4.9 and spark knock

    any pics on what the egr looks like or where it is? ive never worked on it before. thanks

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    HUF
    HUF is offline Cadillac Owners Connoisseur
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    Re: 4.9 and spark knock

    Quote Originally Posted by Brizzal View Post
    any pics on what the egr looks like or where it is? ive never worked on it before. thanks
    Behind Throttle Body , looks like 3" diameter mushroom with a vacuum line attached to it. Please search the archives for EGR , knock, etc. Tons of info. May be a lot of things besodes the EGR valve. Look for vacuul leaks as well clogged EGR tubes inside the trottle body, under the plates.

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