4.9 Distributor / Timing question
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HT4100 4.1, 4.5, 4.9 Discussion, 4.9 Distributor / Timing question in Cadillac Engine Technical Discussion; Alright I've been tinkering with the timing on my 4.9. I don't have a timing light and am kinda doing ...
  1. #1
    Cream_Devil_91's Avatar
    Cream_Devil_91 is offline Cadillac Owners Member
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    4.9 Distributor / Timing question

    Alright I've been tinkering with the timing on my 4.9. I don't have a timing light and am kinda doing it the "old-school" way supposedly. I've advanced it to the point where it doesn't want to turn over easily when starting, and have backed it back a little bit from there.

    My question I can't seem to find an answer to is just how much of a turn on the distributor corresponds to a degree or two in the timing? I think I've been moving it from one extreme to the other with turns of about 1/2 to 1 inch. Can someone give me some sort of idea how much I should be moving the distributor for a 1 or 2 degree change? I ran out of daylight and am going to work on it tomorrow evening.

    Symptoms have been when too retarded: Louder, droning exhaust, loss of power, hot exhaust temps

    Symptoms when too advanced: Starter kickback, acts like it doesn't wanna turn over, pinging

    Can't seem to find a happy medium Really don't wanna buy a 50 dollar timing light for a one time adjustment, hoping I can get it close enough by trial and error. Tomorrow I will try adjusting in smaller increments, but would like an idea of how small we're talking here.

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    Sevillian273's Avatar
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    Re: 4.9 Distributor / Timing question

    1/2" sounds like alot but I've never actually measured.... Each degree is a very small turn of the distributor. I find it hard to move it one degree at a time and usually have to go back and forth a few times to get it where I want so that's how small of a turn each degree is. I would turn it counter clockwise(retarding) in increments until you hear zero ping at every operating condition. I'm guessing that should be around 14 degrees if you run 93. I've noticed that the most sensitive operating condition to ping is at light cruise in 4th with the VCC engaged.

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    Angry Matt's Avatar
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    Do you have any flea markets near you? Last timing light I picked up was a gently used old craftsman for $2. They're good to have around.

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    Re: 4.9 Distributor / Timing question

    One degree of timing for a distributor is about the width of a toothpick, maybe less: the distributor rotates at exactly one half engine speed.

    Get a good timing light and set the initial timing to specs by the Factory Service Manual before you hole a piston.


    "Old school" always set timing and did checks with proper lights and equipment: You cannot set timing, ever, nohow, for any reason, by guess or "feel". Do it correctly or break something, big time.

    Don't forget that you're not only adjusting initial timing (vacuum disconnected), but you're also adjusting every other part of the curve from off-idle to max rpm.

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    Re: 4.9 Distributor / Timing question

    These HEI's are not vacuum advance. I paid $30 for my 'actron' brand light at autozone. Flea market is a great idea. You could also put a want an up on craigslist.

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    drewsdeville is offline Cadillac Owners Master
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    Re: 4.9 Distributor / Timing question

    Timing lights may even be available through the "loan-a-tool" programs out there like at Autozone or Advance. Then it's free.

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    the recluse is offline Cadillac Owners Connoisseur
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    Re: 4.9 Distributor / Timing question

    Quote Originally Posted by submariner409 View Post
    "Old school" always set timing and did checks with proper lights and equipment: You cannot set timing, ever, nohow, for any reason, by guess or "feel". Do it correctly or break something, big time.
    Really? I set all my timing "by ear" and am usually only a degree off at most (no kidding). I used to do it the garage I worked at for "tips". Made good money....

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    Re: 4.9 Distributor / Timing question

    Chris - it's one thing to have shop experience with a lot of engines and setups - it's another to use "turns of 1/2 to 1 inch"...............

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    the recluse is offline Cadillac Owners Connoisseur
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    Re: 4.9 Distributor / Timing question

    ^^^ Touche'

    Yeah, you start moving a distributor that far and your bound to have trouble....

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    Re: 4.9 Distributor / Timing question

    i got a timing light at harbor freight for like $13

  12. #11
    carnut is offline Cadillac Owners Master
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    Re: 4.9 Distributor / Timing question

    This distributor has a lead from the ECM that advances the timing, without that wire disconnected even with a timing light you have no way of setting static (base) timing. On my 84 it was a wire with a green connector. Once disconnected the timing can be read of the timing marks. Spec I believe is 10 degrees BTDC.

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    Sevillian273's Avatar
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    Re: 4.9 Distributor / Timing question

    ^^That's outdated for the 91. You have to jump terminals A and B of the ALDL connector under the dash to get the computer to stop adjusting the timing. The DIC will display 'SET TIMING MODE' and then you can get a reading off the crank.

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    carnut is offline Cadillac Owners Master
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    Re: 4.9 Distributor / Timing question

    Thanks for the correction!! That is the proper step to see the base timing.

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    iamjerry7 is offline Cadillac Owners Member
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    Re: 4.9 Distributor / Timing question

    Quote Originally Posted by the recluse View Post
    ^^^ Touche'

    Yeah, you start moving a distributor that far and your bound to have trouble....
    Yep, if you don't have a clue, you can damage somthin. But if you do a mindmeld with your engine, you can tune it just right. The engine will purr and It will feel right. You'll have to let go of your fear and the left brain, may the force be with you.

  16. #15
    amunderdog is offline Cadillac Owners Connoisseur
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    Re: 4.9 Distributor / Timing question

    Quote Originally Posted by Sevillian273 View Post
    ^^That's outdated for the 91. You have to jump terminals A and B of the ALDL connector under the dash to get the computer to stop adjusting the timing. The DIC will display 'SET TIMING MODE' and then you can get a reading off the crank.
    The 4.9 seems very particular about the base timing.
    As others said.
    Get a timing light.
    Put the system into 'set timing mode' per above.
    Set with the light to exactly what the book calls for.

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