I made a circuit to filter the short pikes from the injector signal.
The idea is that it follows the falling edge immediately, but the rising edge is followed after a short delay.
Also I put some diodes to the ground wire of the mpguino that will raise the ground level of the mpguino about 2 volts higher than the car ground. A diode usually has a treshold voltage of about 0,5 - 0,7 volts in the conducting direction. This fools the mpguino to see a 4,5 Volt signal as a zero. Normally a signal between about 0-2,5V is considered as zero.
There's a 500kohm trimmer potentiometer to adjust the filter so that mpguino will see the pulse as a single pulse (this can be seen on the rpm value)
Here's the signal before and after filter:
And the same thing with more wide throttle:
