"But the 1986 2.3 engine only posts the voltages in the factory manual. "
I do not understand this sentence. Actual values can vary model to model and I don't have them all memorized. I do lots of my testing by feel and recognize the particulars as I test.
Early 190's don't have the ability to go negative with EHA current. An 84 or 85 would fit this catagory, I'm not sure on a 86. The all should give integrater values in duty cycle. Whetehr they can express a fault code by duty cycle also varies. If you get a fixed duty-cycle other than 50% you probably have a fault code indicated.
Bosch Master, ASE Master, L1
33 years MB technician