Tach reads 0 after VST filter cleanout

[corpiscator]

I just had the VST filter cleaned on my 2002 F115 (295 hours). I was having problems with RPM loss. 5800 down to 3200, approximately 30 sec after going WOT. I would lose just enough speed to maintain the boat on plane. The technician believed it was a clogged VST filter.

The engine now appears to have improved throttle response but the TACH reads 0 RPM no matter what I do. I also noticed that the trim meter on the gauge was frozen at 2 bars no matter how I trimmed the motor.

At first I thought the gauge was bad, being the common denominator for both problems, so I installed a new and exactly the same gauge (Standard Yamaha Digital Tach - no command link). The connections were identical and I made sure that the switches on back of the gauge were the same as before and compatible for this motor. Lo and behold the new gauge did the exact same thing.

I now connected the old gauge to a separate power source. It turned on, read 0 RPM, and the trim meter went full bars. I take this to mean that the gauge is working. I now connected this set up with separate power source (12v) directly to the motor at the 2 separate white harness connectors on the starboard side of the motor and cranked the engine. Again, same thing happened as when it was connected to the dash, 0 RPM and 2 bars on trim meter.

Finally I noticed that the trim cam (64E-43139-01-00) was cracked and the trim sensor is frozen. This explains the trim meter failure on the gauge. (Ran out of daylight and was assaulted by too many mosquitos to finish testing the trim sensor for today).

I still cannot figure out why the TACH reads 0 RPM when running the engine. Is there an electronic RPM sender from the motor? What could have possibly been disrupted when work was done to the VST?

Any suggestions appreciated.

 

[Casco Bay Outrage]

Re: Tach reads 0 after VST filter cleanout

To service the VST, one must remove the air intake and manifold. This includes disconnecting several wire harnesses.

Rather that focus on the gauge, focus on the engine. Remove the cowl, and look at each of the harness connections. Unplug and replug the connectors you can reach.

 

[corpiscator]

Re: Tach reads 0 after VST filter cleanout

Great picture, thanks.

After comparing it to my motor I decided take down the intake manifold today and all the wiring appears correctly connected. No corrosion in the connections.

I ran the YDS today and all sensors were registering normal on the software.

The diagnosis record had the following:

Code 28, shift position switch, occurred 0.2
Code 13, pulser coil, occurred 33.7
Code 15, Water temp sensor, occurred 60.4
Code 49, Over cooling, occurred 196.5

I take this to mean that I need to change the water temp sensor at least but I am still at a loss to explain the RPM 0 issue.

I wonder if there might be something wrong with the starboard wiring harness? The YDS reads the RPM's coming from the ECM during testing without any problem.