6.2.7 Injector Opening Retard (*)
You should not have to change this parameter with most popular engine applications. Always set to 0 (*) to start.
This parameter is used to adjust injector phasing – the relationship between injector opening point and the engine’s position in its cycle. Injector phasing is similar in concept to ignition timing – except instead of referring to when a spark occurs, it refers to when an injector opens.
When the ECU receives the crank input for a cylinder, it will wait for this user-programmed amount of crank rotation to occur before that cylinder’s injector opens. For example, if the crank reference angle is 50* BTDC and the Injector Opening Retard (*) is set to 10, the injector will open at 40* BTDC.
(Note: The crank reference angle is given in * BTDC on the compression stroke. The injector opening is given in * BTDC on the exhaust stroke. The 360* offset – to get from compression to exhaust – is hard wired into the injector harness.)
This parameter can be set from 0–700* of crank rotation. Using a large enough number has the effect of opening the injector ahead of the crank input. For example, OEM ignition systems (like the GM HEI) typically have crank reference angles around 6* BTDC. In this case, an Injector Opening Retard (*) setting of 686* would give the same 40* BTDC injector opening position as in the first example. Keep in mind that an engine cycle takes 720* to complete.
The Injector Opening Retard (*) can be calculated with the following equations. One is used for injector opening after the crank input and a second is used for injector opening before the crank input.
To open injector AFTER the crank input
Injector Opening Retard (*) = Crank Ref Angle – desired inj. phasing.
From the first example = 50* - 40* = 10*
To open injector BEFORE the crank input
Injector Opening Retard (*) = Crank Ref Angle – desired inj. phasing + 720*.
From the second example = 6* - 40* + 720* = 686*
The Injector Opening Retard (*) parameter only affects when the injector opens. The amount of time it remains open is based on the pulse width calculated by the ECU. In other words, changing this parameter does not affect the amount of fuel that is injected.
The optimal injector phasing is a function of the intake flow characteristics of the engine. This parameter can be adjusted while on a dynamometer to determine its effect on a particular engine. This is a fine-tuning detail that can be explored once a good basic tune has been established. If you are not sure what injector phasing you want to use, set the Injector Opening Retard (*) to 0 to start.
Note - When running in Bank-to-Bank mode, each injector opens more than once per engine cycle. So injector phasing (in the traditional sense) cannot be controlled. In Bank-to-Bank mode, Injector Opening Retard (*) should be left at 0.
