ECM Fault?

[Akselrud, Boris]

That's me again.
I am just one of those guys who don't take no for an answer.

In short, I did find the anomaly with ECM fuel injector signals which is
causing idle roughness and idle rpm fluctuation. As you all know, in TBI
system two injectors are driven by pulses 1..1.2ms wide and spaced with the
time interval required to make proper air/fuel ratio. What I found by
looking at the signal with an oscilloscope is that there is an additional
abnormal impulse approximately 0.1 .. 0.3 ms wide in between the normal
impulses opening the injector. This abnormal impulse comes and goes,
perfectly corresponding to idle rpm fluctuation. Even when I step at the
accelerator pedal, up to a 2500 rpm I can see the abnormal pulses and again,
they are not always there, they come and go with 1..2 sec interval.
I am also seeing about 70V spikes produced by inductance of the injector
coil and when I put zener diodes to cut them, the engine would barely start.

I am also taking a second cut on the device I've designed to simulate proper
injector signals to the engine. My intent is to see if there is a fuel mode
which would make the engine run smoothly. What I do is disconnect the
injectors wires and connect them to my device with help of which I can
provide accurate timing and play with duty cycle. However my current version
needs to be redesigned properly to absolutely prevent it from opening
injectors for more then  1.2 ms, otherwise I have had a little too much fuel
in throttle body on occasion.

What do you guys make of it?
As you probably remember I am dealing with 1993 Cadillac fleetwood 5.7 TBI

Boris.