Yamaha 6Y5 Fuel Management Gauge not recording GPH

[Mike LaCroix]

I have twin 2004 Yamaha 225's with 6Y5 gauges. the gallons per hour stopped working. upon start up the display works properly. When I start the engines the GPH will read from the port engine only and count down readings from about 8gph to 5gph to 3ghp to 0ghp then a dash line. and it will repeat this several times. The "P" and "S" (port and starboard) indicator's stay off.
I have replaced the three 10amp fuses and checked the connections behind the gauges. I also rang out the wires from the fuel flow sensors to the gauge- OK. Any Ideas?

 

[seasick]

Check all connections at the flow sensors. Hopefully its just a bad connector. If that doesn't help, I would suspect bad sensors. Perhaps someone has the diagnostic test procedures
Did both port and starboard displays die at the same time? If so, I am less inclined to suspect the sensors. There is I believe a 5V reference signal sent to the sensor from the motor. There probably is a fuse on the motor for that 5 volts, I am not sure.

The sensor itself can be opened and checked for an obstruction. The only moving part is the paddle wheel. Be careful, the gasket is not available for sale and if you tear it, you will have to make a new one.

 

[Mike LaCroix]

Thanks for your reply.
The fuel flow sensor is inline with the gas hose. There are three wires coming from each sensor (orange, purple, black). I have checked for continuity between all three wires- NO continuity between all three, on either sensor. The starboard sensor is intermittent and the port is not working at all. I think having a diagnostic plan would be helpful. thanks for the suggestion

 

[seasick]

The three wires will be 5 Volts supply, battery ground , and sensor output ( which is pulses , as the fuel spins the paddle wheel.)
Check at the flow sensor with a volt meter, all three pins relative to ground. One should be 5 volts. I would assume the black is the ground.

 

[Mike LaCroix]

The three wires will be 5 Volts supply, battery ground , and sensor output ( which is pulses , as the fuel spins the paddle wheel.)
Check at the flow sensor with a volt meter, all three pins relative to ground. One should be 5 volts. I would assume the black is the ground.

I have taken voltage readings at the sensors. With the engines running at idle, no voltage coming from sensors (any combinations of the three wires). From the gauge- 5.2v and 2.9v to ground, coming from the dashboard to each of the sensors. Gauge is not registering any fuel flow. Thanks for discussing this with me. I’m lost. I can’t imagine both sensors dying at the same time.

 

[seasick]

The output of the flow sensor is a string of pulses. You need an oscilloscope to view the output. The 5v I mentioned is the power to the sensor. It will read on a multimeter

 

[Mike LaCroix]

The output of the flow sensor is a string of pulses. You need an oscilloscope to view the output. The 5v I mentioned is the power to the sensor. It will read on a multimeter

Thank you for replying. Would it be safe to say that the sensor(s) are faulty or clogged if I'm getting the 5v at the sensors from the gauge? Next chance I get, I was going to remove the sensor(s) and check to see if the impeller is not turning. What do you think?

 

[seasick]

Thank you for replying. Would it be safe to say that the sensor(s) are faulty or clogged if I'm getting the 5v at the sensors from the gauge? Next chance I get, I was going to remove the sensor(s) and check to see if the impeller is not turning. What do you think?

NO.. The data a s mentioned are pulses and you will not see them using a multimeter.

 

[Mike LaCroix]

Thank you for replying. Would it be safe to say that the sensor(s) are faulty or clogged if I'm getting the 5v at the sensors from the gauge? Next chance I get, I was going to remove the sensor(s) and check to see if the impeller is not turning. What do you think?

I removed one of the sensors and it appeared to be spinning freely, I cannot check the output voltage because I don't have an oscilloscope. Would electronic interference efect the gauge from working properly?

 

[seasick]

probably not. Did you check to see if you had a good ground as well as 5 volts on one of the three leads? The motor ignition has to be on but the motor does not have to be running