M84 crank/cam trigger pattern

[eMTea]

Hi guys!

I'm working on a rallycross car, replacing a M48, for a M84.
The car runs perfectly on the M48, but we want some more modern technology.

The motor is a BMW S14 (BMW Motorsport) stroked and bored to 2900ccm.

When trying to transfer base map settings from the M48 to the M84, I can't seem to get my head around trigger setup.

The motor has a 60-2 on the crank, and a 2 "tooth" pattern trigger on the cam (from bmw S38 (M5)).

The 2 teeths on the cam are exactly 180deg apart, and that's what confusing me.

Both sensors magnetic.

The car won't start, no sync.

We fiddled around with various filters, to no luck.
The ref/sync capture shows a relatively clear pattern, but I cant for the life of me understand that it is correct that the cam trigger should have 2 "teeths" 180deg apart? The ecu has no way of determining what phase of the cycle it's in.

It runs perfect on the M48 though :p

I've watched a few webinars on this topic, but they don't get into details to tell if this pattern is an acceptable combo.

[Stephen Dean]

Hi,

It may work like that on the M48 as it is running in batch fire and wasted spark, this means that it doesn't need a Sync input. This can also be setup in the M84 if needed, but it would be better to run the engine sequentially.

You will need to modify the sync trigger to only have single pulse per engine cycle to do this.

[eMTea]

Thanks for clearing up!

We want the M84 to run wasted spark, with seq and staged injection.

[AdamW]

Your photo is not conclusively clear, but it looks to me like that cam trigger has already been modified to effectively give "1 tooth" per cam rotation. It appears that one of the "teeth" is brass so it wont be detected by the sensor.

[eMTea]

The photo is off goggle, but you gave me a reason to check.

Anyway, out ref/sync capture showed us a sync signal for every occurance of missing tooths, so there is something not right for seq firing.

I'm assuming previous owner never got it to work, just left it in place, even when running batch.

[stevesingo]

Your photo is not conclusively clear, but it looks to me like that cam trigger has already been modified to effectively give "1 tooth" per cam rotation. It appears that one of the "teeth" is brass so it wont be detected by the sensor.

This is correct. Only one of the "teeth" is seen by the sensor. I use this cam trigger on my S14 with a 12 tooth crank wheel on M800 ECU.



Can you post a ref/sync capture?

Can you post your cal file?

[Stephen Dean]

Can you post the Ref/Sync Capture thanks.

[eMTea]

Hi!

The engine is apart for the moment, replacing oil rings :/

But before it was removed from the car, it was confirmed, the motor started without the sensor connected. So probably set up for wasted spark as mentioned earlier.

But also, only one of the "wings" were magnetic
As soon as the motor is assembeled, I'll get a capture log.
Stupid as I was, i didn't get one from the dyno when we struggled to start it.
I swear it was a cam pulse for every crank rotation.

[eMTea]

Hi! I'm back!

The Norwegian Championship is over, and we now have time to reinstall the M84 and try startup.

fiesta.PNG (47.09 KiB) Viewed 17725 times

Still no SYNC.

diagnosis.PNG (20.29 KiB) Viewed 17725 times

Please look at the captures attached.

refsynccapture2.PNG (81.22 KiB) Viewed 17725 times

[AdamW]

Your sync edge (cam tooth) occurs right on top of the index tooth (crank tooth following the missing teeth), it needs to be well away from the gap. Preferably 180+/-70deg as per the help file.

You also have some odd noise or distortion of the waveform in a couple of areas of the ref/sync capture, but I suggest you get the sync edge in the right place first before looking at that.