Radio capacitor on EDIS circuit

[David_S]

I am finally getting round to complete my efi conversion by going EDIS-6. A couple of clarifications please.

1) The megamanual shows a 25uF capacitor between the 12 V supply to the coil pack and earth. I presume this is for radio interference suppression purposes. My question is whether this value of 25uF is correct? My local auto electrical parts supplier thought it high but I don't think he knew any more about the subject than me. Any particular type of capacitor recommended?

2) The second concerns the firing order of the Ford coil pack (6 cyl). The Megamanual states that the usual firing order is ACB. I assumed A was the leftmost pair when viewed from the terminal side with the connector at the bottom. I wired it up this way and then checked the firing order by running the engine on the distributor and with the EDIS coil "dry firing" to a second set of grounded plugs . I put timing marks at TDC, 120 deg and 240 deg. This indicated that the firing order for the coil was CAB and when I swapped the two outer pairs of plug leads all was fine. I am just wondering whether some coils fire this way or whether I could have reversed or handed the trigger wheel installation somehow. ( I had considerable trouble with transferring the handing off my sensor bracket as viewed on my back under the truck, to looking down on it at the bench so may have done something similar with the trigger wheel). It all seems OK now in "limp home" mode and I just have to modify the Megasquirt before testing it fully.

Cheers

David

[David_S]

Surely someone has fitted this capacitor? And surely there must be someone out there who knows more about radio interference suppression than I do seeing that I know virtually nothing on the subject.

David

[Heribert]

Any good quality cap in the range 0,1 to 25µF is useful on the +supply to the EDIS ignition coil.
Many V8 had a cap of 0,2 µf at each coil pack, whereas European 4 cyl often used a 20µf electrolytic.
The function is to offer a low impedance circuit for +wire transients to earth, thereby reducing
electrical disturbances from quite a lot.
The cap shall sit as close( ie less than 20 mm) to where the +feed enters the coil pack as is possible and be connected to a solid earth
point with an equally short wire.

The european EDIS 4 as found on Escorts have a nice packaged cap, grey plastic , size of a matchbox, bolts straight
onto ground .
Another option is to take a points style capacitor as found on any car with traditional ignition. Reasonable value and
certainly up to the rigors of under-hood life .
Using a "radio-style" cap is not so good, will probably struggle with humidity, temp and vibration in the engine bay.
But you can of course try, and then get hold of a more sturdy cap.

Heribert

[David_S]

hej där, Heribert (That's almost the extent of my Swedish, I am afraid)

Your information is just what I required. I was going to use an old points capacitor when I noticed that it was 0.22uF compared to the 25uF shown on the EDIS wiring diagram and wondered whether the diagram should have been 0.25uF, especially as the auto electrician only had ones around 0.2uF.

What effect would fitting the smaller one have?

Not sure whether I can get it as close as 20mm to the coil pack though, more like 100mm, but that will be better than nothing.

Tack själv

David

[Heribert]

Hi
A general statement as to the size/effectivenss of the capacitor will only be given by the foolhardy.
It is quite a bit more involved than calculatin Xc and state that the lower the Xc, the better
the function.
If you have a scope , a comparative test valid for your intall is easy enough to make.
The fact that many V8s used appr 0,22µ and European Ford Escorts appr 20 µ is a good
indication that the 0,2µ is probabably quite effective enough.

Best regards

Heribert

[David_S]

Thanks again Heribert for that comment and thanks for your assistance generally through this forum. It is the help provided by guys like you which make Megasquirt so attractive.

I will probably be coming back to this forum shortly with another problem - the perennial "no tach signal with EDIS-6" - but first I must carry out some routine checks along the lines of a recent post of yours.

David

[David_S]

[

.... will probably be coming back to this forum shortly with another problem - the perennial "no tach signal with EDIS-6" - but first I must carry out some routine checks along the lines of a recent post of yours.

Managed to sort out the problem. No voltage at the PIP terminal at the relay board. Found I had reversed the PIP and SAW wires when wiring an in-line plug ...and I am certain I had checked that plug at least twice.

David

[fiftytakedowns]

What is the voltage needed for the capacitor?

[David_S]

What is the voltage needed for the capacitor?

Not sure what you are asking here. The capacitor fits between the 12V supply to the coil and earth (ground) and so the voltage across the capacitor is 12V.

I have been using a 0.2 µf capacitor off the old distributor and it seems to be doing the trick as my radio sounds a lot less crackly, but that could just be because EDIS is inherently quieter than a dizzy system.

David

[fiftytakedowns]

does it matter where the capacitor is grounded in relationship to the megasquirt grounds?

[David_S]

does it matter where the capacitor is grounded in relationship to the megasquirt grounds?

I am not an expert in this field but no, it should not matter. The capacitor is to suppress interference from the ignition to your radio not to the Megasquirt so any good earth close at hand should do. (see Heribert's comments above). I earthed mine to the same point as the original installation as it was handy.

David

[fiftytakedowns]

Okay, thanks!

is there a way to test if the grounding point I have it attached to Is conductive enough...?
ohm reading between block and that point on chassis?

[David_S]

Okay, thanks!

is there a way to test if the grounding point I have it attached to Is conductive enough...?
ohm reading between block and that point on chassis?

Simplest way is to test with an ohmmeter. If in any doubt run a ground cable to the engine block or to your central MS ground point.

As I said before this capacitor is primarily to suppress radio interference and whether it has a beneficial effect on the Megasquirt I really don't know but it certainly won't do any harm to use a common earth.

David