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  1. #1

    Default Strobe can't find timing marks for #1 cylinder

    I went out to check the timing on my 454 this afternoon, and the strobe light could not find the mark on the harmonic balancer even after I verified the strobe was connected to cylinder number one's spark plug wire.

    The only work done up until this point was to pull & clean the rotor and check the cap for cracks. Both the rotor and distributor cap only go on one way, so I don't think I screwed up anything there. The truck fired right up afterwards.

    Out of curiosity, the strobe's inductive pickup was moved from wire to wire until the timing mark was finally visible after connecting to cylinder seven's wire. This cylinder is six cylinders away in the CW firing order (1 8 4 3 6 5 7 2).

    Everything was fine two years ago when the timing was last checked.

    The harmonic balancer looks okay and does not appear loose in its mounting.

    If I were to trust what is lighting up while connected to plug #7, the timing is off two degrees.

    Would anyone care to offer insight into what has happened?

    Thanks,
    Tom
    __________________

  2. #2

    Default

    What year truck? The OBD I units need to disconnect the computer b/4 checking the base timing...My '88 S-10 had a wire under the glovebox at the top of the carpet that had to be unplugged to stop the computer from adjusting the timing. Plugging it in w/ the timing light connected cause the mark to disapear...

    I'd bet this is also required for the newer units w/ OBD II computer since the computer still adjusts the timing.
    Still Loyal to GM after all these years...:shocked:
    2006 Impala LT 3.5L
    2005 Silverado WT small cab/longbed 4x4 4.3L V6
    1999 Grand Am 3.4L in TX w/ our youngest
    1993 GMC Jimmy 4.3L 4 door 4x4 'Ole Rusty' - 'SOLD'
    1988 S-10 small cab/longbed HT3.4L Crate Engine
    1970 Nova 250 I-6, factory 3 sp floor shifter.
    1968 Chevelle 'Nomad' Wagon 250 I-6 w/ 3 on da' tree.

  3. #3

    Default

    1984 Chevrolet C-20 Suburban.

    No computer. The air filter housing instructed me to disconnect & plug the vacuum advance, which I did.

    Tom

  4. #4

    Default

    Quote Originally Posted by TomW View Post
    1984 Chevrolet C-20 Suburban.

    No computer. The air filter housing instructed me to disconnect & plug the vacuum advance, which I did.

    Tom
    That will do it...after checking and locking the dist, we used to hook it back up to test the advance...sounds like you already did that.

  5. #5

    Default

    Out of curiosity why ya checking the timing?
    Is there a miss or some other issue?

  6. #6

    Default

    Quote Originally Posted by wis bang View Post
    That will do it...after checking and locking the dist, we used to hook it back up to test the advance...sounds like you already did that.
    Yep. The whole thing is odd, though. I'm hoping I'm chasing a problem that's due to bad gas. But even though the Mighty Burb is my primary tow vehicle, it does have lotsa miles on it, and I'm trying to rule out a burned valve.

    Checking the timing was supposed to be the easy check.

    Tom

  7. #7

    Default

    Quote Originally Posted by tbplus10 View Post
    Out of curiosity why ya checking the timing?
    Is there a miss or some other issue?
    The truck occasionally flutters or backfires through the carb when the secondaries open while towing a travel trailer.

    I'm guilty of buying cheap gas, though (a practice I am about to stop with this vintage vehicle) but I want to rule out a burnt valve.

    Tom
    Last edited by TomW; 06-05-2010 at 01:23 PM.

  8. #8
    Sr. Mechanic trapperdon's Avatar
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    Default

    on the balancer, are you using a piece of chalk to ensure you're seeing what you think is right?

    did you try dialling it in anyways on the #1 plug until it was visable?
    you sometimes gotta do the stutter & rev method just to get feel for the min/ max...

    when you checked cap, did you take an emery board and sand down the contacts to clean them?

    try pulling the #1 plug (put back into wire) & hold to ground on block to see if you're getting spark..

    something aint done right on plugging your vacuum advance if it doesnt show at all...


    FUEL additive.... stp, gummout, LUCASOIL .....
    :fighting0037:
    when in doubt, doubletap !

    - buying a new truck, one part at a time :grrrrrr:
    94 Blazer 4x4 k1500 5.7 L - aftermarket cold air intake
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    MB Racing rims & Hankook ATm off road tires

  9. #9

    Default

    Quote Originally Posted by trapperdon View Post
    on the balancer, are you using a piece of chalk to ensure you're seeing what you think is right?

    did you try dialling it in anyways on the #1 plug until it was visable?
    you sometimes gotta do the stutter & rev method just to get feel for the min/ max...

    when you checked cap, did you take an emery board and sand down the contacts to clean them?

    try pulling the #1 plug (put back into wire) & hold to ground on block to see if you're getting spark..

    something aint done right on plugging your vacuum advance if it doesnt show at all...


    FUEL additive.... stp, gummout, LUCASOIL .....
    Yes.

    No.

    No.

    HEI is there.

    I hear you, brother. Like I said, checking the timing was supposed to be the easy part.

    LucasOil? get outta here... STP sounds good though.

    Tom

  10. #10
    Legend

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    River Ridge Louisiana-4 miles W of New Orleans-didn't flood-water stopped 800 yards away.
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    Default

    Boy,I should probably just butt out, since I haven't had to use a timing light in 30 years or so.

    However, any chance number 1 and number 7 actually fire at the same time, or more likely fire exactly 360 degrees apart? Waaaay back when some electronic ignitions fired on every cylinder every rotation despite the spark only being needed every 720 degrees.

    If this was so, of course you should still see a firing-and your inductive gun should fire-on plug one. So is it possible that plug one-the spark plug wire- is BAD?? And the plug 7 wire fires the same time as one, so it reads the same as number one would, if one was working right??

    I'm really just guessing here, but if 7 is right, it must fire the same as one?? Maybe??
    Maybe just bad wire bad plug on number one?? This would make it run like crap of course??

    Charlie
    1998 suburban-
    1/2 ton

    199500 miles
    River
    Ridge,LA

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