Bike Died? Phase Sensor Failure by Bill Doll

First the problem: You're diving along and all at once you have a complete loss of power. You notice that the tach drops right to zero even though the engine is still turning. You rotate the throttle only to hear backfiring which gets worse the more throttle you give it. You pull over with the bike dead and restart it. It idles OK but if the RPM's go over 2k the bike backfires and dies. You mess around with the electrical system for about thirty minutes, relays, key switch... then try again. It starts and runs fine. You take off down the road and all is well or maybe not. If you make it home or not, you have just experienced the Phase Sensor going bad. This is the sensor that is inserted in the upper front left side of the engine near the oil-sending unit.

Trouble shooting: I knew it was an electrical problem and that I was losing ignition or fuel, or both. So I built a small panel with three lights on it to monitor power. One to the power supply for the computer, one the coils/injectors/fuel pump, and one the signal side of the power relay. This way when the intermitted problem would show up I could look and see if I had lost power to any of these items. I already had a voltmeter under the seat attached to the TPS for adjustment, so I could check there for 5 volts power out of the computer. I called my brother who has a truck and trailer because I knew that if the problem showed up, I would need a ride home. It was getting dark and I didn't want to try and get home if the problem showed itself again. It didn't take long and luckily this time, it died at a intersection were I could push it off onto the sidewalk. All the lights on the panel were still on, so I pulled off the passenger seat then checked again with the voltmeter, it still had power. This meant it was not a power problem and the only thing left was the phase sensor.

The solution: Well since no one had ever seen one go bad, it was no surprise my dealer didn't have one in stock. A few days later when it arrived, I replaced it. My brother and I went on the test ride. 150 miles later that day I declared the problem solved. This was good because I was headed to the Nationals in South Dakota that week.

So the main thing that made me think it was the phase sensor before I did the trouble shooting, though I had to prove it to myself before spending money on a new part, was the tach dropping off and the back firing that changed with the throttle. This is because the tach gets its signal and the computer counts the pulses from the phase sensor to fire the injectors and spark plugs at the correct time. The backfiring was a sign that this was not happening at the correct time but it was getting fuel.

By the way this is not a Hales effect sensor. Those use a magnet behind a slotted disk that allows the sensor to see the magnet thought the holes. This is a proximity sensor which notes the high and low teeth on the spinning target it's aimed at and has a few things inside it to go bad.

I now this will help those who encounter this fix the problem sooner than I did. Good Luck!
Bill Doll