What's the purpose/advantage of this? My ANHT, AXCN, and AUJP bins all have it de-selected. Any advantage to activating it?

 

Option word 1, bit 6? (did I SWAG it?)

If so, it selects either the ignition +12 v input to the ECM, or the pump voltage +12 v input to the ECM for the injector battery voltage compensation look up argument.

RBob.

 

Understood. So I can look at the two voltage outputs on my scanner. Likely there'll be some amount of descrepancy, but what would be the advantage/disadvantage of selecting one or the other?

 

I always figured it could help determine if the contacts on the FP relay or oil switch were in good condition. Higher resistance could drop the voltage to the pump and the table could try to compensate. There's probably allot of arc when the contacts open and over time may degrade. Or another thought crossed my mind that weakening fuel pump drawing more current on a specific sized wire could drop the voltage to cause the table to compensate. The sense line is connected to the secondary (pump side) of the switches.
It would actually be indicating the system volts too (same as having the bit set), so if all is in good shape its just an extra measure of overkill watching the pump line. Just speculating though.

 

Relays actually need a bit of arc in order to clean the contacts, though I'm sure it also probably erodes them at the same time. I think there might even be a minimum recommended load, such that the arc forms.

But back to the topic, the injectors get power from the fuel pump relay yes (can't quite be sure at the moment, but I always do it that way)? Well, measuring that is the most accurate way of knowing what they're seeing. It's the injector properties (coil/inductance/spring force) that determine the opening rate (not some magical other effect that mysteriously causes more or less fuel to be needed at different voltages). The closing rate isn't affected much by the voltage. The effect is that more pulsewidth is needed to get the same fuel out of the injector at lower voltage, and it's an offeset, not a multiplier effect (once it's fully open, it's open, so long as the voltage is greater than ~6V, but the time getting there is variable).

Assuming the key voltage or ECU supply voltage are the same as the injector voltage isn't a safe assumption, but it gets to the point of splitting hairs for normal operation. Engines aren't super super critical of AFR. If something is dying, that can help a touch, but can't ensure the pump is supplying enough fire water.