Hello Volks,
I have a few defunct Digijet ECU's I'm trying to repair for a backup
and need to test them on the test bench prior to checking them in a
test van. The problem with just simply testing them in the van is that
in the defunct mode, even though the output driver is OK (but the
internal CPU is not running), the ECU activates the fuel pump and
injectors constantly and the engine quickly goes into hydro-lock - the
cylinders fill up with gasoline and the engine won't start or even
turn because gasoline is non compressible. The first time it happened
I was worried that my engine had seized, but figured that obviously
that wouldn't happen with a good motor especially when it's still
cold. I guess those German engineers probably didn't take that failure
mode into account...that's really bad for a failure mode because you
can't just switch back to the good ECU and start the motor, you have
to clear the cylinders first.

Anyway, I'm now testing the ECU's after repair attempts on the test
bench and would like to check the output drivers too. I found out that
luckily the ECU activates the fuel pump relay for a few seconds at
power up (probably to pre-charge the fuel system so it starts
quicker).
Now I want to check the fuel injectors output too. I already know that
without the hall-generated ignition/RPM input signal the ECU halts
both the fuel pump and the injectors as a safety measure (e.g. in case
of an accident, we wouldn't want the fuel pump to spill gasoline all
over the place and risk a fire).
I also know that when in the starting phase (ignition switch turned to
"start") the ECU behaves differently to allow starting.
Does anyone know if activating the start signal causes the ECU to
output injection pulses regardless of the RPM signal?
I'll get down to testing that myself soon, but was wondering if anyone
has already tried this or has other ideas.
Thanks.