1.9td swap.. Tach question

[tdotdub]

My dad has an 1991 Vw golf.. And the car out of the factory was a 1.6D, but 14 years or so ago.. My dad swapped the 1.6d out to a 1.6td... And he got the tach to work perfect... Now 14 years later... Which was today... We pulled out the 1.6td out.. And threw in a 1.9td! But.. For some crazy reason.. The tach is no longer accurate! On idle with the chock in, it reads 1500 rpm.. And with the chock pulled out on idle, the rpm reads 2000! We double checked everything, and looks perfect! The only thing, I can come up with is, the pulley on the 1.6 v belt system was bigger, and the pulley on the 1.9td is smaller...  Could that be my issue? If so, can a resistor or something installed in that wire so it shows a correct-ish reading?

Did anyone else have this issue?

[Thezorn]

I would start off with the alternator pulley, since it is a smaller size. This would in turn rotate more then a larger one tricking the tach, telling it the motor is at a higher rpm then it actually is.
You will need to swap pulleys or alternators to get the right size for an accurate reading.

[tdotdub]

I can't change the pulley sizes.. Since the 1.9td has a serp set up... And the 1.6td had v belt system...

[Thezorn]

I would shoot smokeyEddy a pm, I beleive he has an AAZ in a mk2 jetta. Unless its a 1.6/1.9 head. See what he did or has to say.
If not im sure someone else out there has a bit more knowledge about this that I do

[Vitwagen]

Without adjusting the pulley sizes, you'll need to find a way to reduce the number of pulses from the W terminal of the Alt.

The only thing I've ever come across was here: Dakota Digital LINK

I can confirm, it works great!

[RabbitJockey]

U gotta pull the cluster apart and there's a potentiometer on the tachometers circuit board that needs adjusted

[RabbitJockey]

It will look something like this bu probably has three leads on it

[tdotdub]

It will look something like this bu probably has three leads on it

Thanks.. I'll check it probbly tomorrow.. Where can I find it in the cluster? On the blue printed circuit.. or ?

[RabbitJockey]

its on the pcb behind the face of the tach, its on the passenger side of the cluster

[R.O.R-2.0]

its on the pcb behind the face of the tach, its on the passenger side of the cluster

on my tachs, its on the BACK of the unit, accessible thru a hole in the back of the cluster..

[RabbitJockey]

its on the pcb behind the face of the tach, its on the passenger side of the cluster

on my tachs, its on the BACK of the unit, accessible thru a hole in the back of the cluster..

that could be i've only ever had mk1 stuff apart

[R.O.R-2.0]

its on the pcb behind the face of the tach, its on the passenger side of the cluster

on my tachs, its on the BACK of the unit, accessible thru a hole in the back of the cluster..

that could be i've only ever had mk1 stuff apart

and ive only dealt with mk2/3 lol..

[carrizog60]

does anyboby knows if passat 35i have that adjustement?

[RabbitJockey]

i would think that they do, especially if it was originally a diesel.  the newer gas stuff has the tachometer driven by the computer

[Otis2]

its on the pcb behind the face of the tach, its on the passenger side of the cluster

on my tachs, its on the BACK of the unit, accessible thru a hole in the back of the cluster..

When I was using a Mark II tach to read my AAZ engine speed, I found that the tach's built-in potentiometer did not have enough adjustment range to get the revs low enough to be accurate.

I had to add a resistor to make it work properly:

http://www.vwdiesel.net/forum/index.php?topic=12589.0