aaz with a 92 tach reading to high

[colhel59]

i swapped a aaz in to my 92 gti i also changed the cluster to work with the diesel. But its reading to high, iv read that you can change a resistor and wat not to make it read properly. But all the pics i see are totaly diffrent from the back of my tach can some one help me.



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thanks for the help

[CRSMP5]

what alt set up?? serp? stock?

[colhel59]

its the serp setup

[CRSMP5]

ok... i bet no ac too...

what ive found is due to removing the ac out of it, running a smaller belt.. the alt spins faster..

this is why the tach is off.. say close to 2k at idle??

how to fix.. no idea.. dakota digital thinggy?? i have same issue on my toaster with its tach.. and mykes tdi coupe does too..

so interested in how you fix!! sadly i am no help.. but if your getting around 2k with no ac thats why..

also never seen a tach set up like that.. got maf built into it by chance??

[colhel59]

its say 1500 at an idle. doesnt make sence to me about no ac because the belt may get shorter but the pully size doesnt change which is was give you ur ratio the alt spins at compared to the crank pully. I seen some kind of potentoimeter on the tach also on is in the bottem left corner by my finger and one is right beside the large capasitator. sorry about my bad spelling i guess thats why i never became an english teacher lol

Thanks Colton

[92EcoDiesel Jetta]

You have nothing to lose by marking the potentionmeter and adjusting it and see if it is an adjustment for the tach.

[R.O.R-2.0]

ok... i bet no ac too...

what ive found is due to removing the ac out of it, running a smaller belt.. the alt spins faster..

this is why the tach is off.. say close to 2k at idle??

how to fix.. no idea.. dakota digital thinggy?? i have same issue on my toaster with its tach.. and mykes tdi coupe does too..

so interested in how you fix!! sadly i am no help.. but if your getting around 2k with no ac thats why..

also never seen a tach set up like that.. got maf built into it by chance??

if the big pulley, and small pulley dont change size, then how does the alternator spin faster?

doesnt make sense..

the alt should be turning the same speed weither the belt is 5" long, or 5 feet long, or 5 miles long for that matter..

i dont get it??

[bajacalal]

You have nothing to lose by marking the potentionmeter and adjusting it and see if it is an adjustment for the tach.

Here's a literal pro tip. Use a plastic or wooden something something to adjust it. Although I doubt this is the case, there are adjustments in some sensitive electronic circuits that should be made with a non-ferrous tool, because the adjustable component is small and delicate, and therefore affected by magnetic fields.

[carrizog60]

on my passat i have the same issue.
1.9 engine with serpentine setup and i guess a 1.6 tacho.
try to get a different pulley for the alternator,someone told me one time that citroen 1.9td alt pulley solved the problem.

[fatmobile]

The Mk2 tachs have a potentiometer that can be adjusted, most likely the one by your thumb.
 Hard to adjust because you have to remove the cluster/adjust/replace/ test,.. repeat.
 I moved one outside the cluster on one,.. it was hanging off to the side so I could adjust it with it in the car and running.

[carrizog60]

does the passat clusters are adjustable too?

[colhel59]

adjusting the bottom left potentiometer brought my rpm down its still slightly high a but its a hell of alot closer now. thinking about putting my own potentiometer in places of the original.
thanks for the advice
Colton

[regcheeseman]

adjusting the bottom left potentiometer brought my rpm down its still slightly high a but its a hell of alot closer now. thinking about putting my own potentiometer in places of the original.

You can try but in my experience the chip (SAK215) can't cope with such a short sample cycle and just shuts down when you start to rev the engine - it'll recover though, so no harm done.

does the passat clusters are adjustable too?

they are.

[nathan_b]

ok... i bet no ac too...

what ive found is due to removing the ac out of it, running a smaller belt.. the alt spins faster..

this is why the tach is off.. say close to 2k at idle??

how to fix.. no idea.. dakota digital thinggy?? i have same issue on my toaster with its tach.. and mykes tdi coupe does too..

so interested in how you fix!! sadly i am no help.. but if your getting around 2k with no ac thats why..

also never seen a tach set up like that.. got maf built into it by chance??

if the big pulley, and small pulley dont change size, then how does the alternator spin faster?

doesnt make sense..

the alt should be turning the same speed weither the belt is 5" long, or 5 feet long, or 5 miles long for that matter..

i dont get it??

Yet it still does it, every time.....

[92EcoDiesel Jetta]

ok... i bet no ac too...

what ive found is due to removing the ac out of it, running a smaller belt.. the alt spins faster..

this is why the tach is off.. say close to 2k at idle??

how to fix.. no idea.. dakota digital thinggy?? i have same issue on my toaster with its tach.. and mykes tdi coupe does too..

so interested in how you fix!! sadly i am no help.. but if your getting around 2k with no ac thats why..

also never seen a tach set up like that.. got maf built into it by chance??

if the big pulley, and small pulley dont change size, then how does the alternator spin faster?

doesnt make sense..

the alt should be turning the same speed weither the belt is 5" long, or 5 feet long, or 5 miles long for that matter..

i dont get it??

You don't get it? All you have to change is the size of one pulley to change the RPM of the alternator. On an AC less system, I assume the alternator is driven off the harmonic balancer pulley (crankshaft) and I assume the harmonic balancer pulley is a different diameter pulley (bigger) than the AC pulley to cause the tach to read higher.

You can fix your tach by doing what I did on mmy 92 Eco, which didn't come with a tach. This thread http://www.vwdiesel.net/forum/index.php?topic=20437.0 documents my journey in putting a working tach in it. I started with a Mercedes tach, then a Peugeot tach, then finally a VW gasser CE2 tach/cluster driven by a sensor off of the crankshaft. My tach aslo use the SAK215 chip so it can be done with some modification and calibration. The title of "a real tach" was I have never seen a tach driven from a signal from an alternator on a diesel before (I think only VW does it), which causes tach to be off when you change pulley size. The crankshaft is really the best place to get the signal for the tach, it is not affected by pulley size changes.