Understanding fuel injector operation and causes for faults

Hoping that somebody might be able to shed some light as to what might have caused a fault I'm observing with some fuel injectors.

To give some context I do fuel injector cleaning and testing. I've been doing this for a few years and recently updated to a carbon zapp GS8 bench.

I'm doing some Bosch 2200cc CNG injectors (the variant without a filter basket) from a methanol powered drag car here and am wondering if somebody could explain what might be causing the following...

1. Two of the twelve injectors will simply stop operating during timed, pulsed fuel tests. For example I'm running a 30second pulsed test to simulate operation at 2500rpm and one of the injectors will simply quit part the way through the test. It starts operating, and appears to flowing at a rate consistent with the other injectors, but at some point (14 seconds, 20 seconds, it's not always the same) it just stops firing. Is this indicative of a bad coil? I jhave changed the position of the faulty injector to rule out a bad driver on the bench.

2. None of the 12 injectors stay open during a timed open flow test. The simply pulse once and then close, even though they should be counting down. I have tried other, new 2200cc CNG injectors and not had this problem. Does this perhaps indicate a reduction in coil sensitivity?

Can you put an oscilloscope with a current probe on the injector to see what happens when your failures occur? I think that will help you diagnose what the fault is.

Those do NOT seem to be suitable for methanol, and I suspect the problem is the methanol has corroded the injector mechanisms and they are sticking.

David's suggestion is sound, but involves a bit of messing around.

I'd suggest using the CRO with one input from the 'power' terminal, and one from the 'ground' terminal - perhaps using an adaptor to make things simpler.

Depending on whether they're ground, or power side, switched the inputs should switch from ~12V, or 0V, respectively, on both terminals while closed and ~12v on one and 0V on the other when opened. If there is a faulty coil (OC), when closed the first will show 12V & 0V, and for the second there will be no change of current from 0.0A.