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Old 07-08-2007, 02:42 AM   #1
Scooby Newbie
Member#: 129818
Join Date: Oct 2006
Location: Auckland, New Zealand
1997 GF8 Impreza R6
2004 JDM BE5 Legacy B4

Default Electrical Question, COP -> Wasted Spark conversion

I have here a coil-on-pack equipped 1990 JDM BC5 GT, which is misfiring like a dog (dud ignitor), so rather than replace bits over and over again as one seems doomed to do with a coil-on-pack setup, I'd like to make use of the 2ch 95 impreza wasted spark gear i have here. What I need to know is this. can I combine, pre ignitor, the ECU ignition trigger outputs into pairs directly to drive a 2 channel ignitor? I would say yes from my knowledge (would expect them to be standard transistor driven signal outputs), but would like confirmation from someone with a little more. Otherwise, building an OR gate type setup to drive the ignitor is an option.

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Old 07-08-2007, 08:33 AM   #2
Scooby Guru
Member#: 32792
Join Date: Feb 2003
Chapter/Region: NESIC
Location: lincoln, ri
2003 GGA MBP
12.9 / 105+


well simple form would just be two rectifying diodes to "sum" the two ecu coil driver outputs, but you'd have the voltage drop across the diode (typically ~0.7v) taking some of your spark energy.

it would probably be fine despite that fact.

other than that probably inconsequential issue, i can't see any reason why it would not work. however, i have never done it myself.


edit: if you try this out, consider using schottky diodes instead of normal PN diodes... the lower voltage drop (around half that of PN diodes, or ~0.3v) means higher efficiency and less waste and they are generally much "faster" than PN diodes. the only thing with schottkys is the fact that they are not available in high reverse voltages, and i don't know what kind of flyback you'll be seeing from the coil primaries.
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Old 07-08-2007, 05:44 PM   #3
Scooby Newbie
Member#: 129818
Join Date: Oct 2006
Location: Auckland, New Zealand
1997 GF8 Impreza R6
2004 JDM BE5 Legacy B4


*points out that the mod would be pre-ignitor, not post*

I could probably get away with using a pair of transistor-based OR gates? given the signal is a 5v low current pulse. My main concern is the lag time of the components, and the fact the pack may not get enough dwell time (ive heard that subaru COPs usually use 3 or 5ms, but wasted spark packs prefer 7 or 9)
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