OEM Air Flow

How do we know what method of measuring air flow, MAF or SD, that an OEM ECU uses?

Factory Workshop manuals are often the best source of information. You can also examine the vehicle (or wiring documentation) to see if a Mass Air Flow (MAF) sensor is fitted. If so, it's very likely the ECU will use this for it's primary air mass source, but there may be conditions (faults on the MAF) when it switches to Speed Density (SD).

In some cases both systems can be employed as it's done in Evo X for example, when ECU is interpolating between two data sources...

Specifically I was wondering about a 1999 Corvette with an LS1. It has a MAF and uses MAP. I believe the MAP is default backup to the MAF. It anyone know the answer for sure that would be great.

Anthony,

GM uses a hybrid system of MAF and SD on that vehicle and a great number of others.

I'm oversimplifying, but MAF is used more in steady state operation, SD more in transients.

Like you said, it does run SD all the time if the MAF goes into a fail state, which some tuners induce on purpose.