Tach in Cluster not staying in sync with ECU?

[NOTORIOUS VR]

Having a strange thing happen to one of the cars I'm tuning.

It seems that the tach in the cluster seems to be off past 5000 RPM (by about 300 rpm) and the error increases as the RPM's go up.

Up to about 4k the tach and ECU are correct.  Running 1.1.63 FWIW... Any ideas?  This is the first time I've seen this.  It's a VW Golf VR6 cluster if that makes a difference.

Also on a few cars the tach needle in the cluster will bounce when getting in the higher RPM ranges (6+k).  This is happening one more then one car, I've tried a stronger pull up, and a weaker pull up with no change in effect.

[lugnuts]

Is it a MK3 Sacha?

I've never ever had a problem with the MK3 tachs.

Only Audi's are the pain in the ass.


I don't think I've used that firmware, but I can verify good results with 1.0.78, 1.1.70, 1.1.74, and 1.1.80.

[NOTORIOUS VR]

Yes it's a MK3 VR cluster Kevin.

I'm gonna upgrade to 1.1.74 and see what happens.  I too have never encountered this before.  The bouncing problem yes, but never the tach erroring as RPM's rise.

I'll report back to see what a different FW does.

[mattias]

1.1.74 had a major change in the tach output function, and 1.1.77 has more :
http://www.vems.hu/wiki/index.php?page=GenBoard%2FUnderDevelopment%2FFirmwareChanges

[BigD]

I just realized I have the same problem with an E30 M3 cluster. I calibrated it so it was just about dead on at 1k, 2k and 3k rpm. I try to shift around 7k on the track, then I looked at the logs and the highest I get up to in reality is 6600. Running 1.1.80

[[email protected]]

Obviously the margin of error means a greater disparity at higher RPM

[BigD]

Alright, I'll try calibrating it for the upper range and see how it is on the lower. But I thought I did a pretty good job dialing it in for the lower (ie higher value led to too high reading), although for my purposes, the top 3-4k is what matters.

[NOTORIOUS VR]

So I upgraded the FW to 1.1.47 and the problem is still there.  The tach is off by over 1000 rpm in the top end (ie ~6500rpm on the cluster, but actual is 7600 in VT).

What are the steps for having this looked into?  I will start to verify more cars to see if they're the same now. 

So far I'm betting BigD and I cannot be the only ones with this issue.

[mattias]

So I upgraded the FW to 1.1.47 and the problem is still there.

Why didn't you go 1.1.81 at once ?
With 1.1.77+  firmware you can adjust the dutycyle of the tach signal and try different things, just like I said and pointed out.

[NOTORIOUS VR]

As much as I like trying new FW's... For cars that are making ~600whp I don't like to put on experimental FW's :)

But it's good to know this... Maybe I will try 1.1.80 soon on it and play with the tach settings you mentioned.

[BigD]

How hard would it be to add a tach calibration menu? So instead of having to rev the piss out of my engine, just put in an rpm output value and adjust the divider until they match.

[NOTORIOUS VR]

Good idear!

[NOTORIOUS VR]

Here's a vid of the tach bouncing issue I've been talking about... you'll see it happen shortly around redline.

That has been an issue since 1.0.x FW's BTW.

http://www.youtube.com/watch?v=SR-GWSL9Res

[BigD]

OH, now that you mention it I actually get this too! I've noticed it a few times but generally disregarded it. But I get the exact same thing, with up to and including 1.1.80.