[s-cars] Re. 034 HO Coil w/ AAN ECU?

[Ben Swann]

I would also agree that there is no way the coil could possible ruin the ignition chip
without a major smoking of the whole ECU.  The Fuel/Timing and Boost chips are EPROMs -
they are a permanent memory that gets read only - not written.  They are not volatile
and can only be erased with UV light.   If there is something that is able to ruin the
memory, then there would be major meltdown in other components, such as coil drivers and
logic units as well as the MCU (CPU) itself.  Probably not much short of an EMF/UV pulse
from a nuke would destroy the contents.

The AAN/ADU/ABY Motronic units do use a version of chip that is very picky to program -
this is the "boost" chip - some may refer to it as the "ignition" chip, but most of the
ignition events are mapped into the Fuel/Timing chip.  The boost chip is a
"self-latching" chip that utilizes externat circuitry for reading the chip which is
different than the ECUs in the 3B, MC-1 and 2.   These chips may be susceptible to a
higher failure rate - I don't know.

I would also be interested in any Schematics for the later 5 cylinder Motronic units
incorporating coil on plug circuitry.  This would help with a project I've been working
on to incorporate an inexpensive COP conversion into the earlier distributor based
engines.

Ben

[Date: Thu, 3 Dec 2009 07:50:59 +0800
From: "JC" <jc at j2c3.com>
Subject: Re: [s-cars] 034 HO Coil w/ AAN ECU?
To: "'Mike Sylvester'" <mike at urq20v.com>,	"'Brandon Rogers'"
	<brogers at terrix.com>
Cc: 'Manuel Sanchez' <manuelsanchez at starpower.net>,
	s-car-list at audifans.com
Message-ID: <D4669A87193E4E2EA65A69CB8DB27082 at SUPERSONIC>

Just to chime in here, completely agree with Mike on comments about ignition
coils and "chip failures".  As an incompetent part-time puttering
electronics dork, I have a real hard time seeing how downstream coils could
cause EPROM failures.  Sure if the new coil drivers (whatever they use to
replace the OEM darlingtons aka "POS" - in Americun car terms 'exciters')
drew too much current vs. stock or if there was some flyback phenomena off
the coils or something I could see components in the ECU having trouble, but
it'd be a real long shot, and even then rather than damage an EPROM it'd be
more likely to be a driver transistor/IC or related passive component on the
output circuit of the ECU.  And it does seem like lots of folks have this
setup without trouble.

Having wasted way too much time trying to fix old electronics screwing
around with aged circuits, I would suggest a couple of other
possibilities... If what is happening is that the car develops problems and
replacing the EPROM chip solves it for a while, but it eventually recurs, it
easily could be a bad solder joint or pin connection that gets 'reset' when
the work is done but eventually fails again when the ECU is put back in over
time (with heat a good candidate for contributing factor).   So Brandon
while you say "FACT"... don't rule out a tricky mis-leading symptom. Happens
all the time with old electronics crap that you find replacing one thing
gives a temporary fix but reverts to the failure because it's not actually
the root problem... I had a Luxman integrated amp on the bench a while ago
that seemed to have failed output driver transistors.  Put a new one in and
everything seemed fine, couldn't measure a problem in the unit, but
eventually it would blow. Turned out it was failed solder joints with
micro-cracks not visible to the eye way far away somewhere else on the unit.
The way to confirm in this case would be to have an EPROM reader to truly
test the chip - if that's what your friend has done then I can fully accept
the fact of 'chip failures' but if its just that swappin EPROM chips makes
the problem go away for a while there is every chance that it is in fact
something else.

If it is indeed the EPROMS are failing, then I would say 99% it must be in
the ECU that is frying the EPROM. Has your guy swapped ECU's and had the
same problem with other ECU's?

BTW, is there a schematic for the AAN ECU anyplace? I'm sure the aftermarket
vendors have all either hand-mapped or purchased it from Bosch but I'd love
to peruse one just for stupidity's sake...

>
> By ignition chip, do you mean the eprom that gets replaced in  an upgrade?
> I would find that very surprising that an aftermarket coil could cause the ignition
eprom to go bad.
> That chip is not driving anything external to the ECU.
> It just contains the map.
>
> WRT to the 034 coil solution, I have had these for a few years.
> You can find some installation photos on my site.
> http://www.urq20v.com/My_other_cars/S6/S6_repair.htm
>
> I also went with the 1.8 coils at first and replaced 2 in 2 weeks.
> I now believe that the coil failures are due to bad plugs.
]