I've also to update the engine decoder offset. I've to add 10º and now runs smoother.
this is testing injection cut at 5.000 rpm
You probably don't want to use the decoder offset to tune how the
engine runs. Unlike an old distributor set-up, where you rotate
the distributor to adjust base timing, spark advance is
controlled by the table in the ECUs memory.
The decoder offset is a fixed number for any given engine setup.
It is simply the angle between the synchronization signal and a
fixed crank angle (TDC, IIRC).
A good way to determine the decoder offset is as follows:
1) Load a flat timing table into the EMS, that is a table with only
one timing value in all of the cells. Use a value the engine will
be happy to idle on, ie, 10 degrees or thereabouts. If your
engine has a timing cover with timing marks, choose a value that
appears on the scale.
2) With the fuel shut off (pull fuel pump/injector fuse/relay),
and a timing light connected, crank the engine. Try to determine
where the pulley is when the strobe goes off. Some additional
marks on the pulley can help here. A dab of white paint on the
timing mark helps quite a bit too.
3) Adjust the offset in the direction that will make the strobe
flash closer to the point where the marks line up.
4) Repeat steps 2 and 3 until you get a consistent strobe with
the timing marks lined up.
5) Make a note of the offset, and enter it into your permanent
config. Change the timing table back to one appropriate to run
your engine. Reinstall the fuel fuse or relay.
It is a good idea to start the engine and let it rev, while
watching the timing light to ensure the spark is happening at
the right time.
Once the decoder offset is set, it should not be changed unless
something has caused the trigger wheel timing to change.
If you are unlucky enough to have a newer engine without timing
marks, you may have to determine TDC with an indicator down a
plug hole (or the factory procedure, if different), and mark the
crank pulley yourself. In this case, it might be easiest to use a
flat zero degree timing table.
To get the engine to idle nice, adjust the timing table in the
low RPM cells, rather than fiddle with the offset.EDIT
< AiToR51> ok, thanks for your post. The reason of my change is
because I checked in an engine I've in house without head and
measure the angle between when there is the missing teeth to the
position where is TDC, and it's 90º
AiToR51 pointed out in IRC that he made the change to offset
based on measuring another motor, and not for the purpose of
tuning his idle. This is a reasonable and correct thing to do.