BMW S50B30

I have an issue where after 5500 rpm the third trigger position goes higher, a bit erratic, about 90 degrees higher than where it actually is. Load on the engine doesn't matter, happens free revving as well.

It's not clear to me, but but it could be false triggering (noise) on third trigger input? I may hook up my Rigol scope and check it out. SDA input has 10k resistor in-line, 10nF towards ground and 1N4007 diode for protection.

FIXED Internal 54 kOhm pull-up inside CPU on SDA pin is not enough (naturally), now mounted 2.4 kOhm pull-up to +5 Volt inside ECU before 10k protection resistor.

This is almost certainly due to the next or previous trigger tooth being picked up by VEMS as with 8 teeth there is a 90deg angle between them. I would think this to be a software issue rather then a hardware issue. - Gunni

Details below.

Hardware setup

This is the most retarded position (at rest, cranking) :



Download [triggerlog] and [vemslog]

The measure tooth can be set to 0 or 15 to reach as low angle on the third trigger as possible, 5-35 degrees is recommended. At rest (most retarded) the third trigger occurs at the missing tooth, and every 15 teeth. I've tried other measure tooth settings (0-15 is all that is possible) and I still get this same problem.


Log view of free revving the engine


Fixed the missing/weak pull-up on (SDA) trigger input.


Hello Mattias,

Comprehensive and detailed report, very nice! I reviewed trigger and vemslog, my observations:

Best regards, Dave