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when i put on more electrical load eg lights , at idle speed for example, the af ratios go richer and when its off its lean, what is the purpose of this injector battery offset
Injector battery offset is usually a table that indicates how much delay there is in opening/closing injectors depending upon the battery voltage. Generally lower voltage will have increased "dead times" for the injectors. The ECU will add this delay ("dead time") to the time it opens the injectors.
If increasing the load results in a lower voltage to the injectors, and you are getting rich readings at the same RPM / Load, then perhaps your table should have a smaller delay at that voltage.
It's also possible that the additional load on the alternator has slowed the RPM, (or changed the load) and you are running at a different cell in the fuel table and that should be adjusted.
the table can be adjusted to make the voltage at both high and medium voltage have the same injector dead time, should i interfere with it? or does it serve a purpose
Yes you can adjust the table to keep the AFR consistent as the battery voltage changes. This however won't strictly get you accurate battery compensation tables as the absolute numbers can basically be anything. All you're really getting using this technique is making sure the difference between the adjacent sites is correct. You also need to consider that as the battery voltage changes then the fuel pressure may change which in turn can affect the AFR, so it may not strictly be the injector latency that's your issue. The only solid way of filling out this data is to get accurate battery comp data from the injector manufacturer.
Any change in accessory load will put more drag on the engine, requiring more air or more spark, which could then move you into a different cell in your VE table.
ok thanks guys