TECHNICAL

WHAT IS DIGI-LAG?

This graph was composed by data from a Digi-Logger. Yellow line is the air-fuel ratio (higher = richer)

Under normal driving, the ECU reads off the lambda and trims the fuel to keep the average at 14.7:1 (stoichiometric). This can be seen in the beginning of this graph by the yellow line spiking up and down while the throttle is partly open (Blue line shows rpm). Here the ECU is working to trim the fuel. This is closed loop mode.

As soon as full throttle is applied (WOT), the ECU should switch immediately to the map fuel value and bypass the lambda. However, this is where the Digi-Lag problem occurs since instead of going to a steady fuelling range, the ECU continues to cycle the mixture for a unfixed time period (usually between 1-3 seconds). This can be seen by the continued spiking of the yellow A/F plot even though the RPM's are approaching 6k from a downshift by the tester. Notice the boost is climbing to 15psi and the engine is still going into very lean conditions!

Digi-Lag is the lag in Fuel Enrichment under Full Throttle.

After the ECU finally hits correct enrichment, it only stays there until you change gear and floor it again. As soon as WOT is released, the whole process starts again. So you get Digi-Lag over and over through the gears!!

There is only one solution - SNS No Lag (c) Chip