MSefi.com read only forum (Jan.15,2018)

Today's helpful hint is to make sure that your battery voltage compensation setting is correct. Don't ignore this value and tune around it as I did. If your alternator fails (resulting in the MS seeing a couple of volts less battery voltage) and your battery voltage compensation isn't correct your car will run horribly or not at all.

To top it off, once you adjust the compensation setting to the corect number (0.9 for me instead of default 2.0) you will most likely end up having to retune your whole VE table.

The best time to test this setting is when you've only tuned the VE table at idle. Disconnect and reconnect the alternator (or find some other fancy way of varying the battery voltage) and see what happens. If your setting is correct, there will be no difference in the way the car idles/runs when the battery voltage changes.

How did you determine that the compensation was 0.9?

JAM wrote:How did you determine that the compensation was 0.9?

I kept altering the battery voltage (disconnected my alternator by putting a switch on the excite coil). Then I adjusted the value using trial and error until I found the sweet spot where there was no difference in the AFR or the way the engine ran when the battery voltage was changed.

Thanks, can you tell me what injector you are running? (Hi/Low Z, #/hr, style, etc.)

JAM wrote:Thanks, can you tell me what injector you are running? (Hi/Low Z, #/hr, style, etc.)

Holley TBI injectors, 85pph, low impedance.

Does anybody know if low Z injectors tend to be higher or lower for voltage compensation, or is there no correlation between the type of injectors?