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Default Mercury SmartCraft - Another "Engine Lost Com" - but different?

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micaheli

New member
Hey everybody. I've read through dozens of SmartCraft issue posts about the "Engine Lost Com" error.

My motor: 2007 Mercury Optimax 175 (SN: 1B480255). Everything has been great up to the last ride. Suddenly, the tach went dead, nothing on it. Not responsive to buttons. The speed gauge showed "Engine Lost Com" and no data on it other than air temp (which is a line-local sensor in the helm). The three smaller gauges/analog ones reacted differently. Water pressure gauge went dead/off position but the oil level (remote 2-stroke reservoir) and fuel level both showed correct (as far as I can tell). The engine still starts and runs perfectly.

Things I've tried:
* Removed/Sprayed CRC Electronics cleaner in and cleaned out all connections in the engine harness - then re-seated them all.
* Tried bypassing the junction box and plugging the gauge harness directly into both gauges. Same behavior - blank on the tach, no coms on the speedo
* Made sure both batteries were charged fully from onboard charger.
* Inspected connections at the engine side, everything looked fairly clean. No corrosion to speak of, on the electrical connectors anyways.

What am I missing?

Here are my main questions:
* Would the tacho be entirely blank if it was a smartcraft bus issue?
* Could the ECM be bad, but the engine still run? Could the PCM be bad and have the engine still run?

Where should I go next? My nearest mercury shop (the third biggest mercury dealer in the world) is the shop that okayed this motor and I've had nothing but "meh" experiences from them regarding motors. I'd rather not have to drive this boat hundreds of miles to the next decent shop.

Thanks in advance,
Micah
 
I've tested the terminating resistors according to another post and they all read 120ohms for a total of 60ohm circuit load. I've verified power and grounds. Boat was somewhat recently rewired so all of that is basically new. (and yes, this has all worked since the wiring job).

I am going to order a used 14 pin engine harness to start narrowing down the issue. Since the engine runs great, I am having doubts that it's the PCM - which leaves wiring. Does this seem like the correct troubleshooting path for this issue?
 
There's a small chance I have installed the gauges backward. ie, tacho on the speedo cable and speedo on the tacho cable. Would this destroy the gauges or other components? Perhaps it's just the gauges?
 
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