Here is a simple circuit that should let you use any old voltmeter (analog or digital) as a fuel injector monitoring device. You can adjust the two potentiometers to suit you, i.e. to put the needle in the range you want it to be in.
The transistor is a NPN small signal switching transistor such as the very common 2N3904.
The diode is any silicon diode such as a 1N4001 etc.
The 10k resistor on the input wire insures that this will not affect your injectors or ECU's circuitry since they operate at a very low impedance and this is around 1000 times higher.
None of the component values are too critical since you use the two pots to adjust it to suit.
The "to inj." wire goes to the same place you are hooking the dwell meter.
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