E46Fanatics - View Single Post - Revving Engine Pre-Engine Shutoff
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Old 11-19-2012, 03:25 PM   #16
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Join Date: Jul 2007
Location: Mountain View, CA
Posts: 133
My Ride: Alpinweiß III
Originally Posted by shanneba View Post
Since the fuel Injection for a cylinder happens during the down stroke of the piston and the ignition happens at close to the top of the next stroke, fuel is injected and compressed in the cylinder.
If you turn the key off after the fuel injection and the spark plug doesn't fire you would have unburned fuel left in the cylinder.

BMW made a change with the MS43 ECU to continue the ignition for two more cylinders after the key is turned off.

Page 16 - http://www.bmwmotorsports.org/BMW_docs/m54x5.pdf


"Emission Optimized Ignition Key Off" is a programmed feature of the MS 43 control module.
After the ECM detects KL 15 being switched OFF, the ignition stays active for two more
individual coil firings. This means that just two cylinders are fired - not two revolutions.
This feature allows residual fuel injected into the cylinders, as the ignition key is switched
off, to be burned as the engine runs down.
This seems to answer it. With our cars its absolutely useless because of the additional firing of 2 cylinders. Ohh.. BMW engineering.
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