[s-cars] Is cyclinder 4 just plain bad!

[JC]

Yep count me in that 'problem ECU' list at this point.  I thought the LS2's
were great at first but then realized I still had mild high RPM/Boost
stumble misfires.

Marc was awesome in quadruple checking and trying every possible route
including multiple coil sets (we tried 3-4 by the time it was all over I
think), using known wiring harnesses, setting up a secondary chassis/engine
ground strap, new plugs... Finally I reluctantly had to abandon it and go
back to OEM for the moment.  My ECU wasn't TOO bad, I just got a light
stumble but swapping another "known bad" ECU in my car caused real bucking
dropouts even worse.

Doesn't seem any predictability factor for what ECU's/cars have the problem.
I'm guessing it's some kind of peak current thing and maybe some ECU's
outputs can't supply the current necessary to trigger the LS2 igniters at
high dwell? If it's related to beta on some output transistor being just
below some threshold then there might be no way to predict which ECU's will
or won't work... also could be an aging factor if some output transistor
degrades over time due to heat reducing their gain...  I tend to think the
comparison between the two "Bad" ECU's in my car tends to support this
theory of current supply - one is just below the threshold, the other is
worse.

If spare ECU's weren't so pricey I'd maybe try to explore this theory and
see if there are ways to upgrade the output devices on the board. Slapping a
PC-oscilloscope on the ECU output and logging during road-testing misfires
would be a great step in the right direction. (BTW - is the schematic for
our ECU available on the web by the way? not sure I've ever seen it...)

Anyway - not to focus on the negative - I strongly recommend trying the LS2
sets though as it's the best price/performance as long as you don't have the
problem... and Marc gets full marks so to speak for support...

>
> Before anyone goes this route check with Mr. Swanson of TTV8
> coupe fame as there are some ECU/chipsets that evidently do
> not like the LS2 coils, I think he is working on a fix.
>
>
> Chris
> quite happy with my LS2 system