For those of you who made it to the end of my long post a couple of days ago where only two of the three methods I’ve used in dealing with injector lag were described, here is the third:

The two methods of dealing with injector lag described previously could be considered as working around the basic problem more than a solution to it.  Although the best way to deal with the injector lag effect might be to compensate for it in the controller firmware, we do not have that ability in the field.  Purely as a proof of concept exercise, 1.2 ms was always added to each injector pulse by the addition of hardware.  The results are shown in the attached data plots.  The data was collected directly from the EC2’s into an IPAQ.

Plot 1 shows two idle to full throttle back to idle sequences.  Both sequences were generated after adjusting modes 3 and 2, but leaving the rest of the EC2 parameters and the MAP table at factory defaults.  Data for the manual mixture adjustment and the table value are included to show that no changes in these parameters occurred during the power sweeps.  The green line near the bottom labeled “staged x 10” is the logic signal from the EC2 that is “1” when the MAP is below the staging threshold and “0” when the MAP is above the staging threshold.  These values were multiplied by ten so the staging transitions would be easy to pick out in the plots.  The data on the left is with the normal injector pulses while the data on the right is with the addition of 1.2 ms to each injector pulse.  In each case, the oxygen sensor shows a somewhat rich mixture just prior to staging.  With MAP above the staging threshold, the O2 sensor shows a change to a lean mixture for the normal injector pulse whereas there is no staging mixture change when 1.2 ms has been added to each pulse.  It is important to understand that the 1.2 ms is added to the injector pulses at all times, not just after crossing the staging threshold.  A decrease in RPM is also seen when the O2 sensor goes lean when the normal pulses are used. 

It could be argued that the mixture was more rich to begin with for the sequence with the added 1.2 ms and that is true.  For this reason I've included plot 2.  This is a plot of data resulting from a previous similar experiment with the added 1.2 ms but starting with a leaner condition.  The prop loading was also different, but the mixture is consistent throughout the power range.  Again, this is with all factory defaults except for modes 3 and 2.  It should also be noted that the MAP was limited to about 23 inches due to the density altitude of over 7200 ft at this location.

The simplified tuning as a result of adding the injector lag time to the injector pulses has been demonstrated with my engine stand on the ground and with my plane on the ground as well as in flight.  The favorable effect of this addition is seen not only on staging but also possibly in the low power high RPM descent flight regime.  Although I don’t have a lot of time in the plane yet with this set up, the results so far seemed to be worth reporting.

Steve Boese

RV6A 1986 13B NA RD1A EC2