DIY EDIS Installation

Many thanks to Andrew for compiling this article



For anyone who doesn’t know, wasted spark is where 2 cylinders on opposite strokes are fired at the same time. The main advantage of wasted spark over COP is it means you only need a crank trigger wheel. To use COP you need both a crank trigger and an additional trigger to tell the engine which cycle it's on. Wasted spark has a few advantages; it doesn’t have any moving parts like a dizzy (apart from the trigger wheel), the coils usually fire with a much ‘stronger’ spark that allows plug gaps to be increased, and it also allows higher revving. Not such an issue in a 4 cylinder, more so in a V8, but there comes a point where the dwell time required exceeds what’s available and it won’t fire.

Ford used wasted spark on a load of engines in the 90s (the Zetec was one). They called their system EDIS. EDIS uses a module separate to the ecu. This module decodes the trigger wheel and fires the coils. During cranking it locks the timing at 10* until the car starts and the ecu takes over. The system is very robust and very easy to install as it only requires 2 wires to be hooked into the ecu.

It does have its limits - because of the way it works the most retarded it can go is 10* BTDC. This limits the effectiveness of things such as rev limiters. It also has an upper limit of about 8600 rpm. Loads of ecus (including megasquirt) now have on board ignition drivers to allow wasted spark or COP without the need for external modules.

Anyway enough background, here's my install:

All the EDIS parts were ordered from the UK, except for the coilpack which is off a Falcon (which ran EDIS but without an external module) as postage from the UK was a killer on a coil. The disadvantage of this is there are 6 terminals on the coil, so it does look a little stupid (although there is a spare!!). Maybe I’ll buy a proper 4 cyl pack sometime. The gear cost just under $90 all up (2nd hand, mostly off eBay).

After much searching I decided to make a trigger wheel myself. I got some 6mm steel plate and drilled a 13.5mm centre hole. I then turned up a mandrel that the plate press fitted onto. I then was able to accurately index and drill the 36 holes round the outside. Once that was done I angle ground, turned and filed (all in the lathe) the excess away until I was left with a trigger wheel, all that was left was to grind off the missing tooth.

Next I turned up another mandrel with different diameters to fit the pulley, the washer and the 36-1 wheel. The spindle lined them all up accurately and allowed me to drill 2 holes through for small roll pins. The roll pin only goes about 4mm into the pulley, as I didn’t want to drill too deep. It worked well but next time I'll just have a few laser cut - will be much faster.

Next I welded up a bracket to hold the sensor. The slot milled into it allows the base timing to be adjusted. The sensor gap is set with shims. It is a bit of overkill but I’d heard stories of the sensors vibrating and causing grief. Mine ain’t going anywhere.

Then it was just a matter of bolting everything onto the engine and wiring it all up. Amazingly it started up 1st go. The ignition map I have in is quite conservative but already is a massive improvement over the dizzy. There’s more low range power and a smoother idle. The old dizzy was standard (Sierra) and didn’t match the engine very well.

I had more pics of building and testing it in the lathe but I can’t find them. Here are some of it dummy fitted to a spare block and on the car. The plug leads I’m using don’t fit the coilpack so yes that is electrical tape, not a rubber boot. I’ll have to get the correct ones for it. I also need to tidy the wiring a bit and start thinking about what to do with the dizzy. Still need something there to drive the oil pump and auxiliary pulley.








So there you go, give it a shot. Wasted spark for less than the cost of a Sierra dizzy!! Took me a while of collecting parts and designing how to fit it, but I enjoyed the challenge and now I have an Escort with no dizzy.