This is an old revision of the document!
Overview
The VE table is only used while the ECU is operating in Fake MAF mode. When Fake MAF is selected, the signal coming from the real MAF is ignored above the entered switch over point. For that point on, a MAF signal is simulated by extrapolating from the conditions observed at the switch over point.
Once the switch over point is exceeded, the MAF sensor is completely ignored until the calculated airflow drops well below the clamp point. So as your revs and estimated airflow continue to increase, DSMLink will continue to ignore the MAF sensor. Once you've let up on the gas, the calculated airflow will drop below the clamp point and DSMLink will switch back to using the real MAF signal.
DSMLink uses the volumetric efficiency (VE) table to drive the estimation of airflow once the MAF has been clamped. The adjustment ends up being relative to the VE at the clamp point. DSMLink can also, optionally, use the input from a pressure sensor (Use MAP) to help compensate for boost fluctuation after clamping.
Process
To calculate a more precise VE table for your particular setup, first make sure you’re running a boost level low enough to keep MAFRaw below the typical limit of your MAF. This would probably be around 2700hz on a factory 2G MAF and 2100hz on a factory 1G MAF. If you want to use Fake MAF with a GM MAF/MAFT combination to get a smoother airflow signal, then examine your datalogs to determine an appropriate clamp point target.
With boost lowered appropriately, deselect Fake MAF and set the clamp point to something around where full boost is achieved. Again, datalog MAFRaw to determine this value. Then log both MAFComp and MAFSD. MAFComp is the MAF sensor reading after compensations have been applied to it from the MAF Compensation table. MAFSD is MAFComp after VE adjustments have been applied (as well as factoring in pressure if you have Use MAP selected). Both of these are calculated even when they’re not being used. Adjust the VE table until MAFSD replicates MAFComp. This process will effectively map out the volumetric efficiency of your setup.
