I just had an injector transistor short on my 94 V8 Cougar.
Tracy mentioned he had one fail already in his EFI system.

This is a nasty EFI failure mode. The cylinder (rotor)
misfires strongly. Raw fuel washes
down the cylinder (rotor housing) and accumulates
in the oil sump. Fuel consumption goes way up.
The catalyst (in a car) is super distressed and
smells to high heaven if not failing out right.
The injector burns out. All and all not a fun thing
to have happen. Not to mention you are looking at
$300 for a rebuilt EFI computer and $50 for a new injector.

This would not be nice in an aircraft system.
This is what I suggest Tracy.
A current sensing resistor and some binary feed back to the
computer. You don't need an A/D. A simple quad 311
compartor would do the binary trick.

If the computer turned off the injector transistor and
it did not go off the computer should cut power to the
injector transistor.

It pays to way over rate these transistor.

Paul Lamar

Having had the HALTECH EFI I orginally flew with do the same thing
(fortunately on the ground) I can attest to the bad things that can happen
as a result.  However, if you have Tracy's EC2 and you have wired the two
DPDT switches to be able to shut down each pair of injectors (as shown in
his plans) , you can apply corrective action  and get home on two injectors.
You switch off one set at a time and when you switch off the set with the
grounded darlington transistor the engine will start to run normally and you
can get home just fine with only one set (either primary or secondary).

Of course having the CPU sense this and automatically switch off the bad set
would relieve the pilot of having to do so.  But, then you would also need
some sort of error signal to let you know one pair is turned off as you can
fly with only one pair without realizing it.

Merry Christmas

Ed Anderson

That is a nice feature of Tracy's EFI. Just a couple of LED's letting
you know what is going on would also be a big help. Come to think of
it turning off the power to the offending shorted transistor would 
take another, more or less equal, transistor. So perhaps both could be wired
in series and if one shorted the other could then continue to work
with some sort of LED signal on the dash alerting you to the failure.

Paul Lamar
 
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