ECM Fault?

[Programmer]

Boris,

Get a vacuum pump and hook it up to your MAP sensor. Slowly apply 15 in to
22 in of vacuum to the MAP and note if the idle smoothens out. Let me
know...

Lyndon
-----Original Message-----
From: Akselrud, Boris <AkselruB at moodys.com>
To: gmecm at efi332.eng.ohio-state.edu <gmecm at efi332.eng.ohio-state.edu>
Date: December 6, 1999 7:54 AM
Subject: ECM Fault?


>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.