Tach Fluctuation at high rpms

[Joof]

Hello,

I have seen some mentions in the firmware pages about tachometer fluctuations (or something to that effect) - is this a problem of the vems unit or is this an issue with my wiring?

I have a relatively new unit (May 2012) with pull-up for tacho out.  My tach works fine at idle and through the lower parts of the rev band - until about 4k rpms (though not necessarily every time).  I was under the impression that I did not need a pull up resistor as it is onboard per the spec sheet.  I have also seen mention about wiring in a diode to clamp the load. 

I am not well versed in electronics and figured that if the tach works that there is no need for the diode.

Do I need to wire a diode (possibly one from the rescue kit) into +12 and the tach output to solve this stuttery tach at high revs?  It jumps ~ 500 rpm (i.e. sits at 4k, pulses a few times then jumps to 4.5k and so on)

Probably seems silly but I would like to clarify.  I saw an old thread regarding m50 based tacho and this was the solution but it was my understanding this was before the boards were built with a pull-up resistor.

I do not have any trigger errors in high revs.  Car is BMW M50 (6 cyl) based E36 driving stock tach (divider set to 16) running 1.1.96 config+f/w. Primary trigger is VR (sec-trig disabled, running dual out/wasted spark).

Any insight is much appreciated!

[z0tya]

Try stepper, if free.

[Joof]

Thanks for the reply; as per the spec-sheet/ec-18 pin out it is already on a stepper...Another lad has said that this is firmware related so while I am not terribly worried about it, it is quite annoying.

I recently went turbo and with this new-found power it is difficult to comfortably get on it and not bounce off the limiter.  Hoping a new firmware will solve this? 

Any other BMW M50 people having similar issues?

[mattias]

Car is BMW M50 (6 cyl) based E36 driving stock tach (divider set to 16) running 1.1.96 config+f/w.

Tach output function was improved in 1.1.98. See -> http://www.vems.hu/wiki/index.php?page=GenBoard%2FUnderDevelopment%2FFirmwareChanges

[Joof]

So I shall upgrade to 1.2.0! (?)  Anyone with bmw MXX had any issues with 1.2.0?

I had seen that a while back but forgot.  I just remember seeing "1.1.98 - NOT released (only for testing !) and will never be released"

I imagine that tacho improvement found its way into the more stable f/w's?

Thanks for input btw!

[Erikk]

I use 1.2.0 in a bunch of cars without any noticable problems.

[stroft]

Any other BMW M50 people having similar issues?

1.1.96 same problem.

[Joof]

Upgrade to 1.2.0

It works better, but still not perfect.  The fluctuation is gone but now my fuel cut/rev limit/red line (which is set at 7099) happens at a displayed ~6300 RPM's on the BMW tach on the dash (it revs fine to the vems set redline, just does not coincide with actual numbvers on dash.).  At idle of 900 it shows around 700 on dash, progressively off further you climb through the rev range.
...Better than before but still less than ideal.