BF50 ignition dwell angle problem

Hello to everyone
Please help me
There is a BF50d after 20 h of exploitation. It has problem with ignition dwell angle
Problem occurred suddenly.

Dr.H doesn`t show any DTC during test. Engine speed does not entries more 3000 rpm, ignition dwell angle is -4,5(5 is normal)

I have tested all sensor without Dr.H and everything is ok
Additionally I have changed ECU by new one and still no any improvements in engine work.

What could it be?
thank you for answer

It sounds like you have already taken some drastic measures to change ECU.

This is basic stuff...but...

Did you check the timing marks to see if the timing belt jumped timing?

Did this problem happen all of a sudden?

Did the motor ever run good?

Did Dr. H show the TPS to go to 80% or more?

If you did not mention dwell, I would have asked about quality of fuel, spark plugs, prop size, and of course compression (and valve clearances). Of course, they do still apply. Are they ok?

Did you do a cylinder drop test?

There is nothing in my manual that addresses dwell. I will have to check my latest download for my HDS to see if there is a dwell category.

Mike