Spikes on Engine Speed triggering rev limiter

[Euen Burke]

We are runnning a G4+ Storm on a BMW M44 and seem to be getting random spikes on the crank sensor that are triggering the rev limiter.  See attached log file.  There is not a lot in the log but I think enough to see what I mean.  The M44 uses a 60-2 toothed wheel mounted inside the crank-case, just ahead of number 5 main bearing.  The crank sensor is mounted to through a hole in the block just below the starter motor. 

We tried another second hand sensor but that made no difference and have now replaced the sensor with a new one and rewired from the connector on the sensor directly to the ECU using new screened cable, bypassing an intermediate connector at the firewall.  The spikes only seem to occur after a few laps racing which seems to indicate that temperature may be an issue however the ECT is not going over 90°C. 

After looking at a few similar cases in the Forum I am wondering about increasing the "Limit Ctrl Range" for the RPM limit to see if that helps.  Is there likely to be a downside to doing this?

 

simon log 04022018 race 2.llg

[Adamw]

You have trigger errors, RPM limit settings are irrelevant when the ECU is reporting 19000RPM.  We need to find the cause of the trigger error.

Start by doing a triggerscope (just at idle for now) and attach the scope capture here.

[Euen Burke]

Triggerscope traces (at idle) attached.  19000rpm was only a little spike, there were several to 65K. 

Thanks

 

Trigger Scope Log 2018-02-22 4;38;11 pm.llg

[Adamw]

Hmmm, the trigger actually looks not bad.  There could be a few possibilities...

1. Maybe ignition noise upsetting it at high RPM/load.  Can you explain the ignition system detail a little - wasted spark?  what coils? etc.
2. Some high tooth count missing tooth wheels can distort the shape of the waveform on the tooth after the gap so much at high RPM that it no longers falls through zero, then the ECU doesnt count it as a tooth.  Can you try another triggerscope at say 5000RPM, we may see if it is changing shape.
3. The cam tooth is a little close to the crank "gap".  Although it looks offset to the left enough to not be a problem it is still worth doing a little trick to eliminate that as the potential issue.  Set trig 2 like below and see if you still get the odd spikes.  If you still get spikes then we can rule that out and put trig 2 settings back to how you have them now.

[Euen Burke]

1. Ignition is sequential. Storm feeds Bosch 4 channel igniter which drives 4 Bremi 11 860 coil on plug coils. We have this almost identical setup on 2 cars but the other one has not been giving this problem.  The only difference is that the other is an M42 which has a different crank sensor which is mounted on the front of the engine sensing off the front pulley (still 60-2).

2.  5000RPM trigger scope attached.

3.  Will try that before we get back to the track.  Unfortunately nothing planned for a couple of weeks.

[Adamw]

It looks like that tooth after the gap is starting to creep up a bit in that most recent scope although its still 20V below zero.  It will still be worth trying the trig 2 trick to eliminate that.

[Euen Burke]

Unfortunately the cam sensor is a reluctor as well.  Doesn't give me those options.

[Adamw]

Set it to optical/hall.  This will just shift the point it triggers to the left a little further.

[Euen Burke]

Finally got the car back to the track for testing.  With suggestions above the spikes were still present.  Made 3 more changes.  First was a 1mm spacer under the cam sensor (on the suggestion of our tuner) Second was restore Trigger 2 to reluctor and the third was to disconnect an earth wire between the coil harness and the main common earth point on the engine.  The coil harness included an earth to one of the coil mounting screws via what looks like a choke. On the original harness the earth was also duplicated to the block so I left it in the new harness.  The engine now revs freely to the 7k rev limit without any sign of any spikes on the engine speed trace.  What made this so confusing is that we have 2 cars with almost identical setups and only one was exhibiting the problem. Thanks for your help.