High RPM fluctuation

[yanmar]

HI,
Can someone give me a clue how to diagnose my problem. 
Below 3000 the rpm curve looks very smooth in the log, but then i see sudden jumps up to +_ 100revs. This causes big inj. duty cycle oscillations which disturb my tuning.  I've checked with oscilloscope the trigger signal and it looks pretty good. it is 60-2 wheel and i read the trigger log will not help me. The VEMS firmware is 1.1.96 and IGBT drivers are in use.
I will attach my graphs when find out how to do it.

Thnks,

[MWfire]

Cam sync? Wrong vr polarisation?

[yanmar]

I've checked polarity this weekend, and all was ok. Cam-sync is disabled.
How VEMS calculate RPM? If it is counting teeth only, revs shouldn't jump like that. the oscilloscope shows very stable VR sensor signal at all rpm. Is it possible something else to disturb the calculations?
I don't feel anything when rev the engine, just rpm gauge starts to play.

[gunni]

When it does oscillate in the log can you feel it? Does it ever do it on the overrun or only on neutral / positive acceleration ?

[fphil]

I get also a noisy RPM with jumps which can be indeed of about 100rpm, but only 3 crank trigs are in use in my case  for my odd fire engine. I have concluded that rpm is simply the last angle speed at sync time so the errors are dependent of the engine speed.

[yanmar]

It happens always when the revs are above 3000 (positive, negative, neutral and when hold revs), as the amplitude increases with RPM.
I don't feel it. I was thinking if it is possible to be very light misfire, but the fluctuation appears during deceleration when fuel is cut as well.
Looking now how to insert picture here, but can't find it.

[GintsK]

Some log file?

[yanmar]

tried to upload log here:

http://www.vems.hu/filethingie.php?subdir=MembersPage/yanmar

[GintsK]

Seems rpm doesn't cause problems. But noisy MAP signal does!
What relates to rpm - do you get same non clean RPM line when free reving? It might be because of engine fluctuations against transmission.

[yanmar]

When looking my logs i noticed duty cycle was jumping mostly when rpm play and not that much when MAP play, that's why I pointed rpm sensor. I upload in my files some trigger waves taken at high rpm with scope. They look good, but the voltage amplitude seems low +-1.5V. I want to check if that is normal.
Regarding MAP I have no idea how to test it. Will try with my air compressor first.

[fphil]

Is it not your boost controller acting @ 100kPa?

[yanmar]

yes, it is off below 110kpa. I see no reason to use it when boost is low.

[fphil]

Is it not your boost controller acting @ 100kPa which makes that ripple on the map value?

[yanmar]

I checked the log posted, but see no ripple in MAP value @100kpa. It is very smooth there.

[fphil]

sorry I meant 231kPa