Time to update the calibration in my 06 TT GTO. Since I changed the fuel system to a front regulator return-style with a manifold referenced regulator I need to tweak a few things. I still have the Deka 60lb injectors I started with back in 07. This PCM (E40) has a few interesting internal limits. One of them is the internal scaling of the injector flow table. It does not allow entries above 63.5 lb/hr, even with the use of the additional multiplication maps. As a result you have to scale the injectors a different way. Back when I first did the turbo setup in 2007 the common way was to scale all of the airflow tables and effectively cut them in half. (Note I’m running the HPTuners SD OS with no MAF).

Fortunately someone noticed that you could just change the ‘Stoich AFR’ table by doubling all of those values and then cutting the injector flow tables in half. That gives you an injector flow range up to 127lb/hr. Thanks to Dave Steck for pointing out this idea many times on many forums.

The car stock does not reference the fuel pressure to manifold pressure, so the flow table is not a single value but a table indexed by manifold vacuum. Since the fuel pressure is now referenced by manifold pressure this table is flat.

The injector offset by voltage is a 3D table in the GM world, indexed by both voltage and manifold vacuum. I had a good reference table for these injectors that I need to dig up, as this one is flat across VAC. I need to think a little about this table as a result of the change to a manifold referenced fuel pressure system. It would seem that since differental pressure across the injector is now constant that this table should be flat across VAC.

Most tests of the 60lb injectors seem to show around 62-63 lb/hr(660cc/min) at 43.5psi, and 72-73lb/min (760cc/min) at 58psi (the default GM fuel pressure on this car), thus I have the IFR set to 72.6/2 = 36.3.

My small offset table is almost certainly wrong. I have a graph of flow percentage difference I need to use to make a better table.

What all this really means is that I need to put some ID1050Xs in this car. 8x 1050Xs at 58psi base will be plenty of fuel.

There is still a second limit, the airflow limit, that I need to work around. As it sits now once you are in boost you are in the last row of a number of tables including the ignition timing. This can be fixed by doing a rescale of all of the airflow related tables to that airflow in the ECU represents say 1/2 of the real airflow. A hack, but a hack that works.