Kinda OT: Ford tach in my 914, What the hell am I up to Options

[DNHunt]

Follow me on this you guys.

My ignition is a Ford EDIS system off of an Escort. (Don't laugh it works) Wasted spark, no dizzy and a 2 coil 4 tower coil pack. The problem is that the 914 tach is triggered off of the negative side of the stock coil and it won't work with the EDIS system.

So, I snagged an Escort tach at a pick and pull and I'm going to swap the guts into an extra 914 tach. I just want to verify the connections. It has 3 connectors. Ground and signal in are self explanatory. The 3rd one is labelled B. This has to be switched 12V, right?

Thanks

Dave

[lapuwali]

QUOTE (scott thacher @ Mar 24 2005, 10:04 AM)

i dont know why this is being a problem my tach works fine off of the suby wasted spark, but it is connected to the brain, and that might do the conversion for you. it would be easy enought to make an amp circuit or even a seperate optical trigger to run the tach off the fan hub or flywheel, you could even do a hall sensor with a magnet. i would think the tach signal from the edis should work the stock tach same kind of signal, its just a grounded pulse. just like a temp sensor just pulsed.

As I said, there appears to be a difference between the early and late 914 tachs. You may have a late tach.

This is all hearsay, and I can't find the relevant posts where I picked this up from, btw.

I don't think it's so much the noise as the high voltage that's required. Simply amplifying the square wave from the wasted spark system's tach out should be enough if I'm remembering at all correctly. If you tried to produce a second signal from another sensor, you'd end up with pretty much the same problem, only you're using even more hardware to get there. A simple op-amp or transistor drive shouldn't cost more than a couple of dollars to put together, so if I'm completely wrong, not much loss.

As for the MSD, I've heard tell some people can't get a stock tach to work with that in any scenario, so I suspect the MSD adapter is putting out a clean 12v square wave. It's there, I believe, to filter out the extra pulses from multi-spark setups.

I wish Dave luck, but calibrating the setup is going to be the real bitch on that project. I've got a handful of 914 tachs on the shelf I've considered producing stepper drives for, so you could have a modern drive with a square wave in, and easily switch to six or eight cylinders, all while keeping the stock look. Given how I operate, it will be years before I get around to that project. (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)