More Tach Issues (Update)

[Red Diamond]

Does anyone know where the electronic signal for the tach (Standard/Tourer) comes from. My tach is still not getting the right impulse and won't move until the engine is revved up. It starts when I ride the bike and then it will drop down. I was wondering if the signal comes from the "Pulse Generators" at the timing belts or even the ICM. Any ideas or info will be appreciated.

[valky1500]

You get the tach signal at the negative side of the #1-2 coil meaning the signal wire that comes from the ICM. That's because the dual fire coils are grounded by the very same connection at the ICM. The other side of that wire also feeds up through the wire harness and into the headlight bucket to connect to the tach. 

[Red Diamond]

Thanks Valky, I'll concentrate on that loop, see what I can find. Much appreciated.

[RP#62]

The tach drive signal comes directly from the ICM.  Its the yellow wire with the green trace.  The ICM determines RPM from the pulse generators - it looks at the pulses from one pulse generator and determines RPM, i.e. pulses over a given time (ignoring the missing pulse) and it looks for the missing pulse from the other pulse generator to determine crank position.  Once it knows RPM and crank position, it compares that to a predetermined look up table that tells it which coil to fire and at what crank position, i.e. how much advance to apply based on RPM and crank position.   The ICM also feeds pulses to the tach to give RPM indication

If your engine is running fine, but your tach is not working right, I'd suspect that the ICM is determining RPM ok, the signal is just not getting to the tach, or there's something wrong with the tach.  Check the connector at the ICM and make sure there's no corrosion on the terminals.  Check the bullet connector in the headlight shell on the yellow/green wire feeding the tach.

One other thing to consider.  The ICM is very voltage sensitive.  One of the signs of a failing alternator is screwy tach indications or the tach is inop.  Check your voltage at idle.

-RP

[Ricky-D]

From RP

One other thing to consider.  The ICM is very voltage sensitive.  One of the signs of a failing alternator is screwy tach indications or the tach is inop.  Check your voltage at idle.

There ya go!  That's the best advice you can get.

RP, and a lot of other riders realize how a poorly performing charging system including the battery play in the electronics on the bike.

Simply put, you cannot discount the battery even though it still starts the bike and the alternator sure should be a candidate for a through examination.

***

[Red Diamond]

Thanks all for the helpful information. I followed everyone lead to get a thorough check on everything. The battery is Ok, the alternator is putting out the proper voltage, all the wires are good and connected properly. The problem was the ICM, I installed the ICM from the Tourer and the Tach worked perfectly, all this without the tank installed, running only on fumes. Even at the lowest idle speed the Tach worked. Thank for your help.

[RP#62]

Glad you got it fixed and thanks for following up.  It helps the next guy.
-RP

[Red Diamond]

Another thing I noticed RP, the ICM on this bike was installed with the wires visible from the top side. On my Tourer it was installed with the wires coming out from the bottom. It could have been getting water inside the contacts and caused it to malfunction. (Just a guess), When I get another one, I'll install it with the wire out of the bottom, just as they are on the Tourer. Thanks, RD