Ignition timing problem

[bbs16]

Need some help if possible.

Have a 4 cyl engine with 12 tooth crank wheel with hall effect sensor. Magnetic sensor on chain driven camshaft.
When I run engine on cars original ecu using a timing light the wheel appears stationary (as you would expect)
But when i connect up the M4 unit and use it to power a coil off the car using a timing light again the wheel seems to wander all over the place.
Have used a scope and have put the trigger point of sync sensor between two fall edges of ref.
The wave forms on the scope appear clean with little distortion.
Any ideas?

In the Main setup have:
no: cyls=4
ref sensor=1 hall
sync sensor=mag
ref/sync mode 14 (fall fall)
ref teeth=12
tooth ratio=50 (although help says not needed)
crip=120
ign type=fall trigger
no coils=1

Thanks in advance.

[bbs16]

Well wasnt aware that the sync percentage would change when changed the crip setting? went from 60% to 5-6% redone sync and all is well.

[RossB]

THe CRIP setting should not have any effect on the sync position. What have you "redone on the sync"? It sounds like you may be triggering off the wrong edge.

[bbs16]

Thanks for reply Ross B.
have moved the magnetic sweeper arm anticlockwise on the camshaft to get 60% on the screen. what did before was use a scope to put the trigger inbetween two falling edges of the square wave from hall.
i do see what you mean about shouldnt have any effect in hindsight.

[RossB]

If you are triggering off the wrong edge on your sync sensor the sync relative position will change with RPM as the amplitude from the sensor changes. This will cause a timing error of 30 degrees as the sync sensor edge crosses to the next ref tooth.. You need to make sure that you are using the edge that passes directly through 0 volts.