Voltage

[Shimy87]

I have installed a digital volt meter reading right of the alt in both cars...they both read 14.5 but the SM in both show 13.6ish. Is it common to lose that much between the alt and computer?

[Steve Wood]

Interesting question that I have spent a lot of time trying to figure out.  I have found that a common source of voltage drop is the ignition switch connectors.  Wiggle the connectors and the scantool may jump around...or it may not.

personally, I don't believe the scantool voltage religiously.  It is a digital conversion of an analog signal inside of the ECM and I think with age, it may be close but not necessarily equipped with a decent cigar.

If I recall correctly, I tied my AEM voltmeter into the ecm-ign  circuit and it consistently reads higher than the scantool voltage.

https://vortexbuicks-etc.com/ignition_switch.htm

[phil_long]

This seems to be common. I use to worry about it, but I don't anymore. I just keep my fingers crossed