924Board.org

[Martijnus]

damn. I thought I understood it with the picture you've drawn, but then I realized both plugs fire at the same time.

I think I get the idea.. in a sense, the induction of the coil draws a spark from one end to create a spark at the other end, thus one of two is reversed in polarity.

I would solve this with a diode or something, but apparently that isn't the solution. Any ideas why not? (diode can't handle the frequencies or voltages?)
_________________
"Rule: Turbo's make torque, and torque makes fun." (C. Bell)

924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment

[Min]

Any particular reason your responding to threads posted in 2007?

Min
_________________
Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting.

[Mr Bitey]

[RC]

That`s not my drawing Martijnus, I pinched it from a Ford site.

Actually an EHT diode string could handle the voltage but there is no way it could be successfully applied to rectify the problem. It is inherently the design of the coil and the way it is utilized. Of course Ford`s engineers aren`t fools but that is the compromise they arrived at under pressure from the accountants.

Two individual coils or two parallel earthed windings (per twin lead coil pack) is the answer to this particular problem, however that would also likely necessitate a higher current driver transistor(s), better heat sinking, etc. Economics here again.

Obviously the condition of the plug leads and plugs themselves are more critical than in other systems, since an open circuit here will cause two plugs to stop firing, or a high resistance lead breaking down to either plug will result in misfire on both cylinders.
_________________
World`s quickest 924 2L slushbox

[Raceboy]

And again, twin-plugging the head leads solves the problem by using two coil-packs which means that each cylinder has one coil with correct polarity and the other with reversed polarity meaning all cylinders are equal
_________________
'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold
'84 924, turbocharged, sold.
http://www.facebook.com/vemsporsche

[Martijnus]

I always disliked COP but this is an issue which could change my mind. I haven't had any problems with edis but I can imagine one wants to minimize wear.

I'm glad RC revived this thread because it's interesting stuff
_________________
"Rule: Turbo's make torque, and torque makes fun." (C. Bell)

924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment

[fiat22turbo]

I've had the issue with one bad plug lead taking out two cylinders.

Magnecore wires on the had bad ends and failed. One at a time. Replaced them with OEM wires and ignition problems went away.
_________________
Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

[Horizonblue]

This is very interesting, I never knew that the sparks plugs were series connected on the EDIS system, causing one spark plug per coil pack to wear out faster than the other.

Until now, I was quite interested in using the EDIS on my 924 EFI winter project, but since this "fault" has come to my attension, I will use a conventional distributor.

There is just one thing I wonder about this EDIS system, some electrical guys can probably answer that.

Why are the two plugs per coil not parallel connected in the circuit?

(One side on the coil to ground, the other side to each sparkplug)
_________________
Euro 924, 1976

"If you can't fix it, don't break it"

/P.G. Andersen

[Mr Bitey]

[Horizonblue]

[Min]

[Horizonblue]

[Raceboy]

[Min]

[Horizonblue]