[Diy_efi] Driving injector: forward biased diode between B and C of NPN

[Stephen Webb]

I'm getting my hands a bit dirty trying to reverse-engineer an injector
driver circuit.  The box is actually a K-jetronic control unit from a VW
which drives a "frequency valve", which is more or less a fuel injector.

One side of the injector is always hot, the other side is switched with
what appears to be an NPN transistor, though I could be wrong on that
(couldn't find a listing for the part numbers)  The markings are:

PH ON588  m8827

For now I am going to assume it's an NPN transistor.  Everything about how
it's connected makes sense to me except for a diode which is connected
from the base to the collector.  

Could someone explain what this diode does?  

I'm stepping outside of my normal area of expertise on this, so if this is
basic stuff, I apologize.  From reading TAOE I gather that a reverse
biased diode across an inductive load may be expected (there isn't one,
though there is a 10 ohm, 10 watt+ resistor in series).  Also there is
mention of a base-emitter diode, but I haven't been able to find anything
on a base-collector diode.  


TIA

-Steve


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