Using Megajolt with a distributor

MG David · Post by **MG David** » Tue Jun 02, 2009 3:49 pm

Firstly I should explain why I want to do this. The car involved is a 4 cylinder MGB. I want a budget price user mapped ingnition system and self assembly does not put me off, hence Megajolt. However, I sometimes compete in a class that alows electronic ignition but requires the distributor and carbs to be retained.

So I want to lock up the advance in the distributor and use MJ to control the timing.

Now MJ works with the Ford Edis system and it drives a wasted spark coil pack. In 4 cylinder form that is a wire for each coil plus a common live. I assume the live is always live and the individual wires switch on and off causing the coils to fire.

2 options come to mind and I want to know if they would work.

1) Could I fit only one HT wire to each coil pack, splice them together and take them to the distributor as if they were the HT from a conventional coil.

2) Could I leave the wasted spark coil pack out, splice the 2 individual wires together and take them plus the 12v+ to a conventional coil to get to fire the single coil 4 times per 2 rev cycle.

I realise you can fire a single coil from MegaSquirt but it would be a significant step up in cost with much wasted functionality.

NITROPIXIE · Post by **NITROPIXIE** » Tue Jun 02, 2009 9:09 pm

Hi just to be clear about what you want to do here, basically your trying to keep the look stock and wonder the best way of doing it using this system.

I haven't heard of this being done but it could be worth a try/experimentation if you are willing, unless someone else has achieved this. I've seen other people using the old distributor position to run the VR sensor and trigger wheel. You will still require a VR sensor and trigger wheel somewhere on the bottom end of the engine.

What the EDIS unit does, amongst other things, is set the dwell angle. Ths is the time that a coil/pack is connected to ground. Now every different coil/pack normally requires a different amount dwell, so whether you use the original coil to the dizzy or not could be a case of trial and error. Brent might be able to give you a little enlightenment than myself. But just like the points in an old dizzy, the EDIS unit does also pull the coils to zero, whilst the other side of the coil is always connected to +12v so you are correct in that aspect.

As for splicing the two wires together, it may be best to have two protection diodes in before splicing them together to prevent the two wies of the EDIS unit from shorting out against each other. The circuitry inside the EDIS unit might already protect it from this and if you have a couple spare units, again some experimentation maybe required. It depends whether the EDIS unit operates by pulling the coil to ground and then floats (connects to nothing) or pulls to groung and then +12V. If the latter then diode protection would be required obviously.

You could test this fairly cheaply by getting parts from a scrapyard, ie EDIS, VR sensor and plug leads Most expensive bit probably being the trigger wheel. You don't require the megajolt unit to try this as the EDIS unit will operate at a fixed advance angle only. And if successful then you could obtain megajolt at a later date or if it doesn't work then you haven't lost that much and could probably sell some of the parts off to cover the cost.

If you did test this setup you dont put the spark plugs in the engine, you can setup the engine so that it just turns over on the starter motor (maybe disconnect your fuel pump) and have spark plugs touching the block so sparks can be seen from the plugs to see if it works. If it works correctly like this then move to try to start the engine.

I hope this helps a little but as i don't think its been done before your kind of going into unmapped territory. If you were willing to try this method of keeping the car a little more original then i'm sure you will get a lot of help off this site in doing so and think you would have a lil project on your hands.

Ryan

MG David · Post by **MG David** » Wed Jun 03, 2009 7:06 am

Thanks Ryan, I was concerned that in putting the LT side together the single coil might never spark as one of the 2 wires would always have a connection. Thats why I put the option of joining the HT side together as my first option.

While I new that Edis had a limp home mode I had not thought of using it in the way you say to test the idea before buying the MJ kit. Thats a great idea.

Do the latest 4 cylinder Fords still use Edis or is there a cut off date I need to watch out for?

NITROPIXIE · Post by **NITROPIXIE** » Wed Jun 03, 2009 12:01 pm

I've always found mine on fiesta's mk2's i believe, but there is a wiki page with some info on i have found helpful.

http://en.wikipedia.org/wiki/Ford_EDIS

Most scrap yards don't know what these items do and you should be able to get one at a decent price, they do cost alot new. Normally they will charge more for the coil pack ironically. All my parts are scrapyard parts except the ignition leads, but even scrap ignition leads would be ok to see if you can get everything running right initially.

As for the VR sensor i got a scrap one off a Ford which didn't use EDIS, other people have used other makes of VR sensors i believe, so sourcing one of these shouldn't be a problem.

Another thing to think about is that the distributor may still need to be adjusted so that the rotor arm passes the correct point on the dizzy cap at the correct time. By adjusting the timing on the megajolt, the rotor arm may not be wiping against the correct point on the dizzy at that point in time so no spark will be achieved. Some trial and error here will also be required to achieve the best results.

Post by **brentp** » Wed Jun 03, 2009 6:26 pm

A tough challenge. The wasted spark design requires firing two plugs simultaneously- on in the compression stroke and the other in the exhaust stroke. The high voltage electrical path is this:

cylinder head-> spark plug -> HT lead-> first HV coil pack terminal -> coil pack secondary winding -> second HV coil pack terminal -> HT lead -> spark plug -> cylinder head

So, you cannot leave one of the coil pack terminals connected.

Having the coil drive outputs share a single coil has it's challenges too, as one coil may be 'charging' while the other is firing. This would cause contention for sure.

Can you post a link or paste the text for the rules regarding retaining the distributor? To what degree does the distributor need to be an active participant in the ignition system?

I wonder if you can eliminate the rotor, and jumper the distributor cap internally so the coil pack HV goes through the distributor in a 'do nothing' fashion. A perverse interpretation of the rules, but I've seen far more extreme!

Also note our Megajolt2 roadmap - we do have plans for an inexpensive, distributor-only ignition solution:
http://www.autosportlabs.org/viewtopic.php?t=2294

MG David · Post by **MG David** » Thu Jun 04, 2009 8:11 am

I can see now why I can't just join the HT output together and put it into the dizzy as if it were a single coil.

The reg is below. I have always interpreted it as meaning a functioning distributor by virtue of the first sentence with the second and third sentences providing exceptions. I was looking to get MJLJ in under electronic ignition. Your idea may be worth a try.

3.2.11 Electrical System - The standard electrical system and circuitry must be retained
and be fully functioning as per original vehicle specification. Electronic ignition
systems and sports coils are allowed. Distributor cap and leads are free. An
alternator may replace a dynamo.

NITROPIXIE · Post by **NITROPIXIE** » Thu Jun 04, 2009 11:58 am

hmm tough one that.

Megajolt uses an Electronic Distributorless Ignition System (EDIS), so it is an electronic ignition system. If you can manage to incorporate a dizzy in there then i guess in a roundabout sort of way it isn't distributorless, so is in all intense(? brain fart is that right???) and purposes is an electronic ignition system.
As the second sentence says an electronic ignition system can be used, then hey presto???

Could a coil pack be constrained as a sports coil?? I think not and the original coil or equivalent sports coil would have to be retained.

Megajolt 2 could fit into the Electronic ignition system catergory much easier as it would utilise the distributor more than just asthetics as this would be doing.

MG David · Post by **MG David** » Thu Jun 04, 2009 1:00 pm

Can you tell me what Megajolt 2 is. I guess it is an old version? Is it still available?

A sports coil is one with a gold paint job!

I think if I take 4 HT leads into the cap and then 4 out the scrutineers might complian. Although if the dizzy cap is free perhaps I could use one from a V8 with some reengineering inside!

Thanks

David

Post by **brentp** » Thu Jun 04, 2009 4:19 pm

3.2.11 Electrical System - The standard electrical system and circuitry must be retained
and be fully functioning as per original vehicle specification. Electronic ignition
systems and sports coils are allowed. Distributor cap and leads are free. An
alternator may replace a dynamo.

It does appear the rules are formatted in such a way that it lists a number of exceptions to the 1st sentence.

MJLJ + EDIS *is* an electronic ignition system. Therefore, you are allowed to use it.

Not sure what you can do with the distributor- at best you can remove it and plug the hole; at worst, you leave it there and put a dummy cap over it, since the caps are 'free'.

You should be able to switch over to MJLJ, and not worry about these machinations.

Megajolt2 - see the link I provided above. However, for performance, you *really* want to move away from distributor based ignition.

paulc · Post by **paulc** » Mon Jun 08, 2009 7:33 pm

i took my stock distributor and cut off the top part and created a platform to mount the coilpack. at first glace it looks OEM.

Midas · Post by **Midas** » Sat Jun 20, 2009 5:25 pm

It sounds like the sort of workaround that would result in a seasons running before a 'clarification' of the technical rules, or the source of protest after protest if you finish in the points.

Rich

2002john · Post by **2002john** » Sun Jun 21, 2009 5:32 pm

I was wondering same thing, could you use diode config for tach output as signal to distributer? EDIS output joined for signle output to distributer for trigger.

MG David · Post by **MG David** » Mon Jun 22, 2009 9:31 am

Midas, historically I have not done well enough for the scrutineers or other competitors to take an interest!!!
So I may be safe.