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Engine Specific Info and Questions => IDI Engine => Topic started by: colhel59 on September 15, 2011, 04:40:21 pm
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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.
(http://img851.imageshack.us/img851/4097/sn852492.jpg) (http://imageshack.us/photo/my-images/851/sn852492.jpg/)
Uploaded with ImageShack.us (http://imageshack.us)
hopefully this pic works ;D
thanks for the help
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what alt set up?? serp? stock?
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its the serp setup
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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??
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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
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You have nothing to lose by marking the potentionmeter and adjusting it and see if it is an adjustment for the tach.
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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??
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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.
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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.
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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.
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does the passat clusters are adjustable too?
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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
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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.
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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.....
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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.
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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.....
what still does? what were you responding to? kinda confusing reply..
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I was replying to:
"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??"
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I was replying to:
"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??"
thats like saying a longer driveline changes your rear end gears..
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yet it does change the alt speed... every time lol
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yet it does change the alt speed... every time lol
well, would someone mind telling me WHY, rather than just stating that it changes the speed? i still cant wrap my head around this..
if the crank pulley, and the alternator pulley are staying the same size, and the speed increase is not simply from the lack of an a/c pump, then why does the BELT actually change the speed of things?
i just dont get it. the belt transmits power, it has nothing to do with the speed of things.. a different belt should not change drive ratios.
could someone provide something more than an "it does" explanation? PLEASE?!
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I have never seen a tach driven from a signal from an alternator on a diesel before (I think only VW does it),
My Mercedes Box truck has the tach driven from the alternator...
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I have never seen a tach driven from a signal from an alternator on a diesel before (I think only VW does it),
My Mercedes Box truck has the tach driven from the alternator...
Alot of diesels in boats are driven like this. ive even seen some with a cable drive off the alternator like the old corvettes.
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I think I remember old gasser Mercedes also being cable driven tachs.. anyway, not relevant I guess..
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so, nobody knows if/why the change of a belt size makes the alternator spin faster/slower?
Nathan, you know it makes a difference, so would you please explain to me WHAT makes the difference? why does the alt spin faster when the BELT is the only thing that has changed?
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'cuz it stops slipping... ;)
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so, nobody knows if/why the change of a belt size makes the alternator spin faster/slower?
Nathan, you know it makes a difference, so would you please explain to me WHAT makes the difference? why does the alt spin faster when the BELT is the only thing that has changed?
Changing belt size does not make the alternator spin faster/slower. Changing the pulley size does!
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'cuz it stops slipping... ;)
This seems like the most plausible explanation..
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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
That potentiometer is just a fine adjustment.
You'd have to change the resistor in parallel with the pot to change much,.. seems like lowering the resistance lowers the tach.
Probably a 13k in there now.
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does the passat 35i tachos have that adjustement?
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so, nobody knows if/why the change of a belt size makes the alternator spin faster/slower?
Nathan, you know it makes a difference, so would you please explain to me WHAT makes the difference? why does the alt spin faster when the BELT is the only thing that has changed?
the best way I have wrapped my head around it was to think of the whole belt as a "pulley," make the pulley significantly smaller and the rpm increases relative to the crank. It's just one of those things I guess, I'll admit ROR, I dont REALLY know either, lol.
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My old thread on swapping out the resistor in a Mk II tach to make it work with an AAZ might be what the OP was mentioning in the first post.
http://www.vwdiesel.net/forum/index.php?topic=12589.0
Thanks again to both fatmobile & regcheeseman for all their help with that.
The 13k resistor was swapped for a variable resistor set to about 8.2 k.
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.
What's different with the SAK215 chip in this tach, relative to the chip in the Mk II tach? The variable resistor swap in the Mk II tach worked a treat.