Random ECM/PCM voltage question

[dyeager535]

Just saw a question that triggered another thought/question.

At least with my '165/6E setup the ECM has injector values compensated for by system voltage. Obviously the vehicle runs ~12V normally.

I know some of the sensors (TPS?) use a 5V reference.

How much voltage does the ECM/PCM circuitry "want" to properly run? I was just thinking it would be odd that the ECM/PCM would be a 12V device, yet only compensate for injector PW under that voltage...I would think everything would start to skew as voltage went down?

Not really going anywhere with this, just a question. I've had an alternator die before and didn't notice anything until I got down around 10V, but the truck didn't run any worse, and I just happened to notice the gauge before things started not working right.

[EagleMark]

Don't know if this answers the question... Getting 5 volts from 10 - 14 volts isn't hard.

The injector compensation is USUALLY around 0 at 14.4 volts, as voltage goes down it will increase, if voltage goes up it decreses.

Biggest problem I've found is relays start to turn off around 10 volts or less.

[RobertISaar]

the processor itself and all of the ICs run 5V, but they do so via regulating the ~12-14V the battery/alternator is supplying. you would have to drop the system voltage down to ~7 volts(or possibly less) before those start having power supply issues. as Mark stated, relays and other relatively high-current components will start acting oddly when getting too much below normal battery voltage.

[dyeager535]

OK, that makes sense. At least on my "ancient" TPI setup, with the mechanical oil pressure switch for the fuel pump, I guess down to ~7V or so, it should still run?

Not really worried about it, I just had never thought of a voltage drop (alternator death) in terms of anything other than injector PW, since that is what the .bin shows as voltage adjusted.

[RobertISaar]

fuel pump would be turning quite slowly with only 7 volts applied to it.... coil probably wouldn't fully saturate unless the ECM accounts for low voltage in it's dwell calculation.... injectors would be opening VERY slowly....

basically, everything would get very sluggish, though still somewhat functional.

[ony]

on a 16144288 ecm i was using the pulse with correction vs battery volts to increase fuel to ajust the bml, some cars i have worked on when the altenater goes above 15 volts the ecm goes crazzy some of them would shut off and you would have to restart them.