Trigger setup for Audi S4, 5cyl Direct Fire engine

Audi 2,2T AAN engine

1.0.29 + MT r027




1.0.25 + MT r027





Notice drop in RPM, engine never catches up


Possible causes

These explain everything we've seen!



Too high amplitude at the missing tooth.

Eliminating this would likely help a lot. The first attempt did not help. Unfortunately the welding has different magnetic characteristics, so it's a bit different that if the wheel had been machined that way.

You can fill up the small corner-step which leads to the tooth after the gap (considering the rotational direction. before the gap: we don't care):


A [factory wheel] which gives good signal.

You can even make the fill (the red part) muuuucccch longer than on the pic, eg. 1.5 tooth long, to span halfway until the gap-mid, don't be afraid of it. The patch you applied seems to have much lower B/H ("magnetivity") than the base material (not the same material, right?). Even if you filled most of the gap with that material, the the pulse would be just a tiny bit smaller than the normal teeth.

Do you plan to make this ?

Note: no need to mount the wheel on the engine to measure the missing-tooth amplitude. (change the voltage divider 100k/1k to 10k/1k if the notebook sees too low signal)

Also, amplitude varies a lot for normal teeth as well, likely because excentric shaft or wheel. Amplitude is bigger where the sensor sees higher "magnetic flux rate of change", eg. because wheel gets closer to the sensor or has higher magnetic permittivity (mu=B/H).

Most likely reasons:

Note: wheel must be mounted on the engine to measure if shaft is centered.

TODO: Is the sensor mounting bracket firm ? Yes, made it even stronger but signal is the same

The 2 captured waveforms show exactly the same pattern, so it is very unlikely to be caused by vibration (why would the sensor vibrate exactly with the same phase each time?).

Possible workarounds

Even if the signal remains trash, it might be possible to solve the problem

Normally, the (relative) times for a 60-2 near the missing tooth:

with reverse polarity:

the moving average periods will be

This means that the first period=2 will trigger (since >1.5*1) but the second will not (since 2 < 1.5 * 1.5). However, this is a bit too sensitive to rely on. Eg with lengths:

the moving average series:

Which means the 1.8 will be correctly detected as a missing tooth (since 1.8 > 1.5 * 1) but the second will also, since 2.2 > 1.5*1.4. This is what prevents you to start with reverse polarity.

However, with the advanced multitooth trigger you can configure missing-tooth threshold range to be 1.625 (13/8) .. 3.5.

Any luck ?

Status as of friday:

My mechanic welded as the picture above, didnīt solve the problem but since i have to be at the tyreshop i havnīt been able to make any measurements.

Got a new triggerwheel from Holms today (no weld in gap)

Will try this during saturday.

ECM is unclamped at the moment. (not too easy to measure inside or solder LM1815pin5 jumper for max arming threshold...)

ECM: 3.3 #332 "preassembled"

This means that you have 180k at the LM1815pin7 (the higher this resistor, the higher tolerance to pulseheight variation, but less tolerant to random noise).