MoTeC Global Forum

Greetings. I have just joined the forum. I do have a bit of experience with the M84, but I am currently helping to debug an issue with a system that was installed a couple of years ago and is now experiencing some random sync errors. This car is a very good running car and the tune seems to work very well.....and then....sometimes there is a sync error and it either dies...or runs funky until it resyncs....... This install is a Porsche 911 with 3.8RS engine, ITBs w/common plenum, COPs etc.
I've reviewed the tune setup, logs etc and I've replaced the cam and crank sensors (both Hall)...reviewed/changed grounds.....and i just cannot spot the cause.
I've attached the tune file, log and cam/crank capture file.

Please review and let me know if you can see what is wrong and/or have ideas for further actions.

regards,
al
the x-faktory

I think you should be using Rising Edge for your Ref Sensor Edge Polarity. This will require changing your CrIP value.
It's unlikely that is your problem however.

From the Ref/Sync capture, there is some timing differences in the sync signal between two subsequent cycles (sync falling edge @ t=0.01224 and t=1.0872 and t=2.0502) -- it looks to me like it moves about 1deg-- you might want to check the chain tensioners on that engine !

I suspect you have an intermittent connection in the sync sensor wiring. Wire broken at a terminal crimp either at the ECU or sensor end. Sync Error is most likely a dropping of the Sync signal which looks like an extra sync pulse.

BTW - there is a hole in your fuel map, 2000 RPM / 60 % throttle, 18 probably wants to be 68

David,
Greetings and thank you for taking the time to review and respond.
Regarding the hall sensor and rising or falling edge polarity.....can you let me know why you think Rising edge is preferable for the Ref sensor. I've attached the Motec tech sheet for Hall sensors and this lists that either Rising or Falling is ok, with Falling edge as preferable.



I appreciate the detail regarding the Sync signal drift...this was pointed out to me earlier, but I didn't put it together with timing chain slack.....thanks for that.

An intermittent connection does seem the most likely...i've checked....but i will check again and maybe just redo it.

....and, nice find in the fuel map....fixed!

regards,
al

That data sheet shows a hall-sensor that is low when there is no trigger detected, so the missing tooth gap would be low, which is why they recommend using a falling edge. Since your sensor is high when the gap is detected, I suggested using rising edge. Basically I like to use the last edge before the gap to indicate which direction to take.

Now with a magnetic sensor, you need to determine which edge has the most "vertical" form and choose that.

Hope that helps.

David,
Thanks, that makes sense.
regards,
al

i think there may be some confusion due to the Motec_Hall document. It is showing what I would consider to be a vane sensor which goes to the High output state when the vane is within the sensor (by blocking the magnetic field across the slot). I expect the engine in this case has a Gear tooth sensor on the crank which goes low when the tooth aligns with the sensor end. Which is opposite to the linked document. Therefore Falling would be the correct edge for the Ref sensor, and this is supported by the capture showing high across the missing teeth region, then falling as the first tooth after the gap occurs. Also, gear tooth sensors typically switch faster on the falling edge (eg, Honeywell 1GT101DC sensor Switching times: Fall 1.0 uSec, Rise 15 uSec) so it would be preferred where possible.

For the Sync, as David noted, there is some scatter but as the engine was doing about 1250 rpm for the trace the scatter is probably going to occur regardless of the tensioners. Between the 1st and last Sync -ve edges there is about 3 crank degrees difference. However, for that Ref/Sync mode the Help says the Sync edge should occur 180 +/- 70 degrees before the Crank Index tooth. By my reckoning, only the positive going Sync edge meets that criteria. If I understood the Help correctly I think you can change the edge without needing to change the CRIP angle.

With all the crazy values when trying to restart the engine I think there is probably a grounding problem.