Tach signal

[camfromchilla]

Hi all,

I very recently picked up a 96 Valkyrie here in Perth that has had an EFI conversion done to it. The trouble is that the tach doesn't read correctly and there is no adjustment in the ECU for its tach output.

I was hoping that someone on here might know what signal the stock igniter sends to drive the tach. The only info I can find on it is that it is some sort of 12v signal.

The ECU is putting out a 12v square wave but this seems to make the tach read too high. Anyone have any experiences here?

Tomorrow I will try getting a signal from the neg side of an injector and possibly try some resistance in the line.

[indybobm]

I am sure that many people would like more information, pictures on the EFI conversion.
You said that the tach does not read properly, does it read too high, too low, erratic?
Does the Valkyrie still have the factory ICM or has it been replaced as part of the EFI conversion?
Stock Valkyrie has the tach driven directly from pin 16 of the ICM which is driven by the Ignition Pulse Generators.

[camfromchilla]

The tach reads too high but is stable.

The conversion was done long ago by PO and either they didn't know our didn't care that it reads too high.

I plan on getting a lot of pictures and details to share as I get more idea of what's happening with the conversion.

The new ECU replaced the ICM and I believe that it directly reads from the original pulse generators. I will know more when I take the timing cover off for belt replacement.

The ECU drives the coils using this module
https://www.bosch-motorsport-shop.com.au/3-channel-ignition-module-bim203

[Bagger John - #3785]

All a tach is, is a simple linear frequency counter.

Per the factory service manual or other accumulated data: How many pulses occur during each revolution of the crankshaft? Divide by that number to get an accurate RPM signal for the tach. One can design their own tachometer-driver circuit, and I believe some companies (Dakota Digital, etc.) offer conversion modules to do same.

[indybobm]

From the data sheet, it looks like it is for 3 channels than can handle a maxium of four coils. since the Valkyre sparkplugs fire on each revolution of the crankshaft, I would think that the module should see it as a three cylinder motor. It read high by what per centage?

[John Schmidt]

I mounted a tach off a VTX 1800 on a friends Valk some years ago. I just remembered how we used to hook up an old dwell tachometer back in the days of distributors with points. Did the same on his conversion and worked fine. Might look into that.