[bartmanS4]

Anyone know what the difference is between the PCII and III?
Also, when you install a PCIII how does it work? It doesn't replace the stock ECU right it just plugs in series with it?

 

[infoage1]

Right, the PCIII works with the ECU (inline) and changes the signal to the injectors, plus or minus "x" percent.

Not sure the difference, but I don't think there is

 

[btkacs]

The PCIII has a self correction program to optimize the mapping when you are mapping it on the dyno, whereas the PCII has to be adjusted manually (on the computer one grid at a time) and then ran on the dyno again to check the results. Also the PCIII carries an option to adjust ingnition timing.

 

[Speeddog]

As far as I've found out, the PCIII only has ignition timing control for some bikes, and Ducati is not one of 'em.

I think your only option for an S4 is a PCIII.