Shift Interrupter Switch Bypassed - 4.3 MPI

ajmoore88

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Aug 19, 2018
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1
Hey All,

New user here and thanks to the help from this forum I was able to diagnose my engine cut out issues. Turns out, my 4.3 MPI has the engine cutout issues that plague some older MPI engines. More details on the following posts if interested:

http://www.marinemechanic.com/merc/distributors/mercurymarine/sterndrive/gmefi-nostart.PDF

https://forums.iboats.com/forum/eng...l-mpi-2002-merc-engine-cuts-out-for-no-reason

My question is, I have bypassed my shift interrupter switch in order to solve the problem. According to the above bulletin, the proposed fix by Mercury is to shell out over $2000 for a new ECM.

Since my boat is running fine using the bypass, I thought I'd ask the forum what could happen if I continue to run it with the shift interrupter switch bypassed? Any possibility for damage to the shift cable or gears?

If there is a compelling reason not to keep this fix long term, are there any alternatives to getting a new ECM? Could I get it reflashed with new software instead?
 

Bt Doctur

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Aug 29, 2004
Messages
19,481
You wiring supplies a voltage signal to the ecm, it does not ground the coil on earlier systems. Its a simple switch that closes on contact. The switch helps coming out of gear in the water and should never move on land
 

alldodge

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Mar 8, 2009
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If there is a compelling reason not to keep this fix long term, are there any alternatives to getting a new ECM? Could I get it reflashed with new software instead?

I'm assuming since you have the switch you also have an Alpha drive, because the Bravo does not use the switch.
Did read in the other thread that the other guy bypassed and had no issues. Since your able to go from Neutral to Forward or Reverse while in the water without issue, then your not going to damage anything.

The switch is used to unload the dog clutch in the drive by making the motor stumble. Only caution I would mention, is be aware of this issue, because you may be docking at some point and not be able to get the drive back to neutral

The ECM can be tested/repaired for less depending on which one it has
 

Bt Doctur

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But then again we`re all just guessing without the drive info or engine serial number
 

harringtondav

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May 26, 2018
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This switch momentarily kills the engine allowing the dog clutch to disengage
The increased shifting effort could shorten the life of your lower shift cable.

I don't know anything about the ECM interface. My '96 simply grounds the coil B+ primary. It may be possible for you to bypass the ECM and directly ground your coil thru the switch.
 

alldodge

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The MPI motor switch disconnects power when activated, no grounding.
 

Bt Doctur

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Aug 29, 2004
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