Yamaha 6Y5 Tachs going Haywire

[eelpoint]

Hello All,

I’ve had a few of the smartest Yamaha techs try and figure this one out. We are all perplexed.

quick summary:
2002 Yamaha HPDI twins connected to Yamaha 6Y5 (2YC) series Tachs, speed and fuel management. Prior to going in the paint shop in Florida and then a long haul (on a trailer) from Florida to Mass the gauges worked as they should.

All bullet connectors are hooked up properly and display correctly, however as soon as the orange, gray, pink, black 4 pin connector is connected to the back of the gauge all indicators light up like it is in a self test mode, to be specific not the backlight display for night running I’m talking about all the digits and the warning bars… the tach reads “88”. It stays in this mode until you turn the key off, and then when you turn the key back on whether you start the engine Or just leave the key in the “on position” This will continue to display. I’ve checked the dip settings inside the tach and they are set as they should be with the first one up and the second two down.

I have even replaced a key switch to rule out possible black module in the key switch being faulty. Was met with same results as original key switch.

Does anyone have any ideas or what could be the problem both tachs are behaving the same way. Not just one.

[99yam40]

what all was done to the boat and motors at the paint shop.
could they have damaged the ecus or gauges themselves?
lightning strike while sitting in storage or on the road maybe.

pull the gauges and see if they work properly on a different motor/boat

or try a known good gauge on your setup.
you need to figure if you have gauge or ECU problems

[eelpoint]

99YAM40 - thank you. Good idea. Follow up question are the four pin ivory colored connectors that run from the gauge into the rigging tube then back out to the outboard? Is that a one piece wire bundle or are they connected like the bullet style connectors so when rigging a boat you’re not destroying the ivory plastic pieces like you would in a very tight tube. I’m asking because when I updated the fitting from the bracket rigging tube to the fitting on the engine itself, I gave the wires fuel and oil cables, a pretty good tug and could have dislodged the bullet connectors.

[99yam40]

sorry, but I have no idea.
hope someone else can answer your question

[boscoe99]

The control box, and the ten pin harness from the motor, have nothing whatsoever to do with the trim/oil warnings (over temperature warning as well) that is displayed on the 6Y5 tachometer.

[eelpoint]

Why is it if I plug these 4 pin connectors in do the 6Y5 tachs show 88 rpm 8888 hours and every warning signal u illuminated with either key on or engine started when I disconnect that four pin wire tachs behavior they should. This happens on both outboards and their corresponding TACHS

[99yam40]

is there a chance the wrong plug was hooked in

[boscoe99]

How old/new are the tachometers?

[eelpoint]

I recently acquired the boat in March. To the best of my knowledge the tachs are 2002, same year as boat and motors. I brought the boat from Key Largo to Fort Lauderdale on its own bottom after purchase and the tachs worked as you would expect them to. I then had it hauled on a trailer from Florida to Mass, did some overdue maintenance on the engines, fired them up on a hose in the driveway and all was working as it should. I dumped boat in the water a week or two later and that is when the tachs started going haywire. I could understand one harness misbehaving, but two? Could it be a grounding issue?

[boscoe99]

Why is it if I plug these 4 pin connectors in do the 6Y5 tachs show 88 rpm 8888 hours and every warning signal u illuminated with either key on or engine started when I disconnect that four pin wire tachs behavior they should. This happens on both outboards and their corresponding TACHS

Have you tried disconnecting one of the four pin connectors at a time to see what happens?

[boscoe99]

Grounding issue? Could be anything. But both at the same time is strange.

Maybe connect and disconnect the bullet connectors to the tachometer (power, ground and tachometer signal) to see what, if anything, happens.

[boscoe99]

What maintenance was performed?

[eelpoint]

I've done similar with Eric from GaugeSaver. We started with one connection (yellow) to one tach, then tested by turning key switch to corresponding motor on. If we were successful we then went to green then test, black then test, blue then test, We then connected the Fuel Management and Speed gauge (similar procedure) Yellow then test , Black then test, Blue then test, Red then test, Green then test, Green/white then test. We then moved onto the Port Tach and connected that separate from Starboard Tach, Fuel Management and Speed Gauge... all tested good. Then we moved to the 4-pin connectors and as soon as we connected the Orange, Black, Grey 4 pin connector (not the Pink wire according to the label) gauges went into cardiac arrest. I can try this test in the reverse method as you suggest, would expect same results No?

[boscoe99]

I am still confused by everything working fine on day X and then on a later day it does not. On two different systems.

[eelpoint]

Fuel - VST, Fuel water seps, primary fuel filter, spark plugs, med pressure fuel filter, OS sensor cleaning (I used MAP fuel, which I found out later is too hot for the O2 sensor... I didn't loiter on it, but I def used MAP)

Other: Lower unit service, water pumps, T stats, new fuel pipes on med pressure filter. All odikar clamps.

Only Yamaha OEM parts