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TDI tachometer calibration

Printed From: The Brick-yard
Category: T3 Section
Forum Name: Useful threads.
Forum Description: All old, but useful threads will be dumped here so they don't get lost!
URL: http://www.brick-yard.co.uk/forum/forum_posts.asp?TID=15470
Printed Date: 16 Jan 21 at 11:09
Software Version: Web Wiz Forums 12.01 - http://www.webwizforums.com


Topic: TDI tachometer calibration
Posted By: angry vanagon
Subject: TDI tachometer calibration
Date Posted: 04 May 07 at 23:41
hi has anyone had trouble with there factory diesel tacho reading obviously high after a tdi swap using the serpentine belt setup rather than original jx pulleys and alternator? checked with VAG COM and engine speed was around the 870 rpm mark at idle but the tacho reads around 1300rpm was looking at re-gearing using a petrol crank pulley but this would reduce water pump speed or trying to find a bigger alternator pulley but most seem to be the same size, anyone had a simular experience?    



Replies:
Posted By: Full Throttle
Date Posted: 05 May 07 at 09:04

Are you using the original T3 tach clock.

I did'nt notice this as i used the electronic golf one and will be removing it for the T3 Tacho when i put it back into my van.

I assume i will have the same problem.



Posted By: T3di
Date Posted: 05 May 07 at 11:50
you can recalibrate the tacho..........(IF you know which screw to turn)........but if you can hook up something that gives the true reading then,it can't be that hard.....can it??--trial and error on the pots on the pcb is worth a try,just remember where the screw position was originally.






or am I talking boolox again...........


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Posted By: Full Throttle
Date Posted: 05 May 07 at 20:19

Do they have pots on the back of them then to adjust them.

Looks like a frequency generator, squirt the equivelent for 1300 rpm then adjust it to 870rpm on the tacho.



Posted By: angry vanagon
Date Posted: 06 May 07 at 10:14

Originally posted by syncrot4 syncrot4 wrote:

you can recalibrate the tacho..........(IF you know which screw to turn)........but if you can hook up something that gives the true reading then,it can't be that hard.....can it??--trial and error on the pots on the pcb is worth a try,just remember where the screw position was originally.






or am I talking boolox again...........

have you done this on your van with tdi motor? 

has anyone gone down the alternator pulley resize route? 



Posted By: angry vanagon
Date Posted: 06 May 07 at 17:36
strippped clocks today found calibration potentiometer so i reconnected the wiring plug to the pcb and plugged into the tacho unit, started the engine and tacho was reading 1300rpm turned potentiometer anti clockwise slowly and adjusted down needle to 900rpm now rechecked the tachometer against vagcom measuring blocks pleased to say it now reads within about 50rpm at 1000/2000/3000 rpm reassembled & reffited clocks road tested 


Posted By: Ghia
Date Posted: 06 May 07 at 18:03

Would this be the said potentiometer?

And it's accessed through this hole which you need to make through the white sticker. Then you don't have to take it to pieces like I just did .

MG



Posted By: T3di
Date Posted: 06 May 07 at 19:41


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Posted By: Ghia
Date Posted: 06 May 07 at 20:57

I've just been out and calibrated mine by using a gear calculator and satnav for accurate speed. Mine was miles out but I'm fairly sure it's due to an incorrect alternator having been fitted.

MG



Posted By: Full Throttle
Date Posted: 06 May 07 at 21:46

cool pics, i suspect i will need to do this when i use the T3 clocks.

Nice one guys.Thumbs Up




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