based on my experience and what i've had in my hands... low impedance should be around 3 ohms high impedance are usually around 14 ohms.
if you want to get more specific there is a site out there that lists all the denso injectors, with flow rates and resistance.
for toyota (as a generalization) the square connector injectors are almost always the low impedance where as the rounded connectors are high impedance... again this may not ALWAYS be true but from what infomation i have gathered it seems to be the case. Hope that helps.
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