Clock driver circuits in processors are designed to drive high capacitances and low impedances, this maybe your low reading, still a bit unusualif the chips not powered.
Also the i/o of a microcontroller or processor with i/o will have protection on the output pins, this will give you a low reading.
Try the test again and this time with the meter set to diode drop, if you get 600mV or thereabouts no problem, zero ohms then that could be something wrong.
If your measuring across the power pins maybe your meter is trying to power the circuit, and thats not going to give meaningful readings.
I'm glad my boat doesnt have electronic engine management, its a good old fashioned cav injector pump & pintaux injectors.
I know a little about Abc, jm, and napier engines not from the marine industry, from generators.