Here's a situation I encounter quite often
During diagnosis, I want to determine if the mass air flow sensor(s) [MAF(s)] is/are healthy.
I hook up an OBDII reader to a vehicle that I'm trying to diagnose and get access to real-time mass air flow rate.
By knowing the engine displacement and RPM, I can estimate the volume of air that the engine should be pushing through. However, because of the concept of volumetric efficiency, the calculated and measured values will be quite different, related by the equation below.
Measure air flow rate = VE x Engine Speed x Displacement ( x unit conversions )
So bottom line, knowing volumetric efficiency at a known point of engine operation would enable one to look at the measured value and tell if the MAF is reading what it should.
Is there a rule of thumb that would allow one to roughly estimate what the volumetric efficiency of an arbitrary fuel-injected gasoline engine is at a given point of operation? If it helps, I don't mind limiting the scope of the question to engines with single throttle bodies.
As an example, "VE is 15% at idle RPMs", but it should be accurate enough to tell whether the MAF sensor readout indicates significant degradation of performance of the sensor itself.
Announcement: The Great MAF Experiment is underway
The aim is to attempt to objectively answer this question and your data can help the community potentially discover this rule of thumb. Thanks in advance!