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  1. #1
    Cadet
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    Default Mercruiser Thunderbolt V ignition problem?

    Boat ran perfectly last fall. Purchased it, brought it home, winterized and stored it. This spring, it won't run. Starts easily, engine accelerates smoothly and quickly, like it's off to the races, but it craps out in less than a second. Like the ignition was shut off. Every time. I siphoned out all fuel, replaced with new, pumped new to carb. Tore down and cleaned the carb (looked clean already). No change. Lined up all the plugs in a grounded row in firing order and watched them spark 1-6-5-4-3-2 each in turn.

    I grounded out the purple/white (to go into base timing mode), but it makes no difference, does exactly the same. So do I have a problem with the T5 ignition module? Is there any way to take the module offline and run the engine without it? (For testing only).

    The previous owner told me he had the same problem last spring and he just boosted and cranked until it started, then he ran at half-throttle for "a while", then it was good for the summer.

    Is there enough info here to confirm I should just go purchase the Delco Voyager EST system?

    Or is there some drop-dead test I should do to prove beyond any doubt that the T5 module is toast?

    Thanks for any guidance.

  2. #2
    Captain AllDodge's Avatar
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    Default Re: Mercruiser Thunderbolt V ignition problem?

    I would run through this and it will let you know which direction to take.

    http://www.boatfix.com/merc/Bullet/83/83_24.pdf
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  3. #3
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: Mercruiser Thunderbolt V ignition problem?

    That bulletin is for a TB4 ignition, the OP has a TB5

    Here is the chart for the Thunderbolt V

    Don S.


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  4. #4
    Fleet Admiral HT32BSX115's Avatar
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    Default Re: Mercruiser Thunderbolt V ignition problem?

    Quote Originally Posted by fixxupp View Post
    Boat ran perfectly last fall. Purchased it, brought it home, winterized and stored it.

    This spring, it won't run.

    Starts easily, engine accelerates smoothly and quickly, like it's off to the races, but it craps out in less than a second. Like the ignition was shut off. Every time.
    So it DOES start EVERY TIME?

    Sounds like you have a working ignition system, that quits after you do something.............. after you do WHAT? Move the throttle?


    Is this an Alpha? Maybe it's a maladjusted cable/ shift interrupt? Or the WHT/GRN wire from the shift interrupt to the ICM chafing/grounding out on something etc......
    73 de Rick
    ----------------------------------------------------------------------------------
    I use xxx oil and have never had a problem........
    1987 FourWinns 211 Liberator, 7.4L- Bravo III installed by ME,
    Formerly OMG 460 King Kobra powered
    1947 Stinson 108-2 Station Wagon
    , Franklin 6A-335B. Hartzell CS 2-blade prop
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  5. #5
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: Mercruiser Thunderbolt V ignition problem?

    What is the engine serial number?
    We only know it's a 6 cylinder, and that only by the firing order.
    Year, carbed or EFI,

    You could have nothing more wrong than a bad ignition switch. Turn the key to run and see if you have battery voltage on the + terminal of the coil.
    Don S.


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  6. #6
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    Default Re: Mercruiser Thunderbolt V ignition problem?

    Yep, starts every time. Don S. nailed it, no coil volts with key in Run position.

    Admiral, you nailed it too "...quits after you do something..." Yep, it quits after I let the key return from start to run position.

    Not yet sure how to zero in closer, but you fellows have been a great help getting this far.

    Thank you very much!!

  7. #7
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: Mercruiser Thunderbolt V ignition problem?

    Check the voltage at the ignition switch on the purple wire. If no power there, replace the switch.

    Still need to know what engine ya got.
    Don S.


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  8. #8
    Fleet Admiral HT32BSX115's Avatar
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    Default Re: Mercruiser Thunderbolt V ignition problem?

    Quote Originally Posted by fixxupp View Post
    it quits after I let the key return from start to run position.

    Not yet sure how to zero in closer,
    You just "zero'd it in right there!!
    73 de Rick
    ----------------------------------------------------------------------------------
    I use xxx oil and have never had a problem........
    1987 FourWinns 211 Liberator, 7.4L- Bravo III installed by ME,
    Formerly OMG 460 King Kobra powered
    1947 Stinson 108-2 Station Wagon
    , Franklin 6A-335B. Hartzell CS 2-blade prop
    -
    All PM's cheerfully answered! Please ask tech questions in the appropriate forum so everyone's included

  9. #9
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    Default Re: Mercruiser Thunderbolt V ignition problem?

    Don,

    Sorry, the boat is a 2001 Mariah, 4.3 Mercruiser (GM) V6, carburetted 2-bbl, Alpha outdrive. Too hot & humid to stand on my head in the engine compartment searching for the serial number, but ifya insist, I will do your bidding in the relative cool at the crack-o-dawn.

    I removed the switch, it seems good, in run position there is continuity between B(attery) and I(gnition) terminals. So does this mean I need to chase the purple ignition wire through the harness, looking for an open or a ground?

  10. #10
    Fleet Admiral HT32BSX115's Avatar
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    Default Re: Mercruiser Thunderbolt V ignition problem?

    Instead of checking for "continuity", check for full battery voltage at the ICM/dist when you release the key.

    And while you're at it, check the battery terminals, and all fuse, switch and ground connections for corrosion and looseness.
    73 de Rick
    ----------------------------------------------------------------------------------
    I use xxx oil and have never had a problem........
    1987 FourWinns 211 Liberator, 7.4L- Bravo III installed by ME,
    Formerly OMG 460 King Kobra powered
    1947 Stinson 108-2 Station Wagon
    , Franklin 6A-335B. Hartzell CS 2-blade prop
    -
    All PM's cheerfully answered! Please ask tech questions in the appropriate forum so everyone's included

  11. #11
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    Default Re: Mercruiser Thunderbolt V ignition problem?

    OMG!! This boat is REALLY new to me, I didn't even do the buying checkout myself (and my son didn't mention it). While I was lying on the floor reinstalling the ignition switch, I noticed an on/off switch on a bottom left corner of the little panel where the shifter mounts. I had never noticed it before, I have never seen it on any other boat (even though I have bought/repaired/sold Mercruisers of vintage '87 to '96 in my golden retirement years). I have no clue as to its purpose, but I switched it ON and fired up the engine. It stays running!

    I 'fess up cuz the embarrassment helps motivate me to be smarter in the future.

    Sorry for wasting time, mine and yours. For me, another lesson learned.

    And thanks again. This is an excellent resource!

  12. #12
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: Mercruiser Thunderbolt V ignition problem?

    It's the lanyard kill switch. Glad it cured your problem. The odd thing, is that shouldn't have been the problem. There isn't anything that bypasses the kill switch in the wiring.
    Don S.


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  13. #13
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    Default Re: Mercruiser Thunderbolt V ignition problem?

    It's curiouser and curiouser, cuz it's a labelled toggle switch, not lanyard style. Looks OEM, not an afterthought modification. I can see rationale in a "secret location" security switch, but I cannot understand why the builder would have wired in a plainly visible switch that does half the job, ie, lets it fire up, but not run. (Could it be the builder was out of lanyard-style stock and just threw in whatever would fill the hole?)

  14. #14
    Petty Officer 1st Class mr300z87's Avatar
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    Default Re: Mercruiser Thunderbolt V ignition problem?

    It is possible the starter switch is bad and the toggle is the quick fix to hotwire it. I had to do this to a car I owned long ago while I waited for the new switch to come from Japan.
    1989 Invader V210 Cuddy Cabin
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  15. #15
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: Mercruiser Thunderbolt V ignition problem?

    Here are a couple pictures from a 2001 owners manual.

    control.jpg lanyard.jpg
    Don S.


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