[s-cars] AAN Ignition Coil Info (Long)

[David Forgie]

AAN Ignition Coil Info (Long)
The AAN 20 valve five cylinder turbo engine is related to the 3B 20 valve five cylinder turbo engine that Euro and the US got in the early S2 coupe (Europe) and the 200 20vt (including the US but not Canada). 
One of the fundamental differences between these  two similar but different engines is the ignition system. The 3B used a hall sensor-equipped distributor and a single coil.  The AAN uses five coil-on-plug (COP) (PN 034 905 101) coils and two three channel (PN 4A0 905 351A) power output stages (POSs).  The ECU controlled the ignition via the POSs and inputs from a cam position sensor, a crank position sensor, an engine speed sensor and a manifold absolute pressure sensor, among other things.
This is a link to the OE ignition PNs:
http://forums.audiworld.com/showthread.php?p=23784217
Here is a link to the various ECU inputs and outputs that are involved with the AAN ignition (if you are curious):
http://forums.audiworld.com/showthread.php?p=18945405
The AAN ignition system has generally proven to be very robust and, in addition to allowing an increase in horsepower and torque over the 3B (e.g. stock 227 hp AAN  vs 217 hp for the 3B), it also eliminated the nasty “spark hop” problem that occurs in high hp 3B engines (especially when the wrong (wide) rotor is used (instead of the proper narrow 3B rotor).
To replace the OE ignition system, you will find the “351A” POSs run around $200 each and coils run around $125.  Coil to plug boots are around $5 to $25, depending on your source.  As a result, a complete OE AAN ignition replacement would cost over $1000.  The upside is it would likely be good for 100K miles or so.
One of the weak points of the AAN ignition is the power output stages (POSs).  They are basically transistor-based switches and, as such, fail in a number of different ways.  Here is some POS info from Sept. 2005 (some updates since then):
http://forums.audiworld.com/showthread.php?p=18806037
Based on the failing POSs that result in missing and failing coils that also result in missing, in the summer of 2005, I decided that I wanted to develop an alternative to the OE AAN ignition system, just so there was one.  I decided to use the 1.8t coil packs (even though I knew that they had been the subject of a recall).  I went ahead with this in Aug/September 2005 and “published” a DIY in early October 2005:
http://forums.audiworld.com/showthread.php?p=18808309 (also available as a pdf on S-cars.org)