F6A coil on plug conversion?

[Brad Austin]

Searched and didnt see anything. Wanting to convert from distributor to coil on plug for the ea11r/f6a motor. Has it been done or can it be done?

[Ian Linden]

Since the timing is totally ECU controlled, I don't see why it would not work, but I've never heard of it done.

[Murray Betts]

My first reaction is that it would be a very involved job on the Capp.
The standard ignition is with one coil and a distributor/rotor arm to send the sparks to each cylinder in turn. The timing trigger is inside the distributor, you set the timing by moving the distributor body on the cylinder head. The ECU will have only one coil driver with no cylinder identification associated with it, that is done by the distributor physically. The ignition map will be within the ECU, speed/load related with a spark timing referenced to the distributor trigger signal.

In order to make a coil-on-plug system work it would need in principle 3 coil driver circuits and each one identified relative to engine cycle (e.g. no.1 cylinder compression stroke etc). The cylinder ident is usually done with a camshaft sensor, the crank angle for the ignition timing map usually with a separate crank position sensor. I can't imagine adapting an ECU from a different engine would be an easy job, there are plenty of 3cyl engines around now including turbo units which use on-plug-coils, but you'd need to be ble to adapt and re-map it to suit the Capp engine.

There have been aftermarket 3cyl electronic ignition systems which use 3 coils and fire them all together 3 times every engine cycle (I have an old Triumph Trident which has such a system), but this introduces waste sparks. You get the proper spark somewhere just before TDC compression, let's say typically 10-40deg BTDC or thereabouts, then another one 240deg later so a little way up exhaust stroke, then another one 240deg later so roughly half way down the induction stroke. With a naturally aspirated engine this waste spark on the induction will work without setting the mixture off because there is always some residual exhaust gas and the relatively small amount of incoming charge is largely diluted by it and outside the range of combustibility although I was always rather suspicious of it, however with a turbo engine it would be highly risky as it may well be high enough pressure/temp and enough fresh charge to ignite, including back into the intake manifold. I would not consider such a system.

When all is considered, just getting the std system into top condition would be my suggested route. Obviously a distributor cap and rotor arm with HT leads is always going to be prone to issues (that's why modern engines went away from it, the majority of faults with older engines were ignition related), but if components are in good condition it can work fine.
I use one grade colder than standard plugs because I run the ignition advanced a couple of degrees (feels much livelier and with 95RON fuel there is little risk, it was calibrated for 91RON and was probably significantly knock limited at lower speeds). Extra advance increases plug temp, something like 10-15degC per degree of ignition advance at higher engine speeds, so a couple of deg advance justifies one grade colder plug. NGK and Denso do suitable items, NGK stock item is a DCP7EVX, I use an DCPR8EIX (resistor, iridium vs platinum), the Denso equivalents are 22 stock and 24 colder, for example Denso VXU24 (check for yourself if choosing something non-standard).
The only potential issue is cold fouling but if you do a cold start and allow the engine to idle without touching the throttle for about 30sec you'll be through the crank/afterstart enrichment so little risk of fouling. I did once measure the injector on-time for a start and most of the enrichment ramps off in the first 10sec or so. Don't blip the throttle when cold, it will provoke fouling.

Let us know i you find an answer.

[Ian Linden]

Oops, I take back my previous post. I didn't realise that the wasted sparks would give rise to problems with a turbo.

[Brad Austin]

Oops, I take back my previous post. I didn't realise that the wasted sparks would give rise to problems with a turbo.

Well thats the thing, I'm running the keisports stand alone ecu, totally programmable. Basically get rid of distributor and put a cam/cas sensor in to tell ecu when to fire. Maybe use a ford crank sensor setupike megasquirt does? Dosnt the newer 95+ k6a cappuccino use coil on pmug ignition? Maybe its adaptable?

[Ian Linden]

.... Dosnt the newer 95+ k6a cappuccino use coil on pmug ignition? Maybe its adaptable?

I think the answer is no, but I don't know as much about these things as I would like. Take a look at Fig 50 in the EA21R Parts Catalog in the Manuals section. What do you make of it?