How to get a tach signal from 3 coils ?

ad francois · Post by **ad francois** » Thu Jun 29, 2006 9:50 pm

I have a Goldwing 1500 6 cylinder (boxer) for which I want to use the negative coil wire as tach signal. I am using the megasquirt V2.2 and have 2 throttle bodies, each with one injector.
The engine has 3 coils (1 for each pair of cylinders) and is firing one coil each 120 degrees.
I did attach the tach signal to one coil on which I could start and run the engine. My fear is that 2 squirts per engine cycle is too little. Therefor I tried to hook up the other coils to the tach signal, but here I get stuck.
I am not that familiar with electronics, but I know this has to be done by using diodes. I tried a wiring diagram I found in the MSN-extra description to hook up multiple coils for the tachometer. This diagram is using one zener diode (3.3 v) and for each coil a normal diode (1N4004). I tried this, but without positive result. Is there anyone out there who can help me with a schematic how to derive the tach signal from 3 coils?

jsmcortina · Post by **jsmcortina** » Fri Jun 30, 2006 3:13 am

I would try using one coil and pretend you have a 2 cylinder engine. Provided the rpm is displayed correctly it doesn't really matter seeing as you are fuel only.

James

ad francois · Post by **ad francois** » Fri Jun 30, 2006 10:08 am

This is exactly the condition I'm running on now, but as it's a 2*3 cylinder I want to have at least 3 squirts in a cycle, and if possible 6.
I'm worried about running some cylinders too reach and some too lean.
Do you have any experience with TBI and do you think it really matters ?