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Aftermarket Tachometer
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jsmiller
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PostPosted: Tue Feb 03, 2015 4:51 am    Post subject: Aftermarket Tachometer Reply with quote

Ok I'm sure this has been covered on here but after searching I couldn't find an answer! I have a 1990 caravelle (vanagon) 2.1 digifant. I currently have an old crappy aftermarket tach installed and it works fine (never had a factory in dash tach, it has the clock). So, here's the issue, I bought another tach (better looking, bigger etc) and it basically doesn't work! The needle just bounces all around and it's unreadable. So I thought the tach was broken. But I've heard it could be due to the signal from the ecu or the coil doing this? And that this is a digifant only thing? I had and 84 vanagon (digijet) years ago with the very same tach I'm tiring to install and it worked great! So surely someone has the answer? If it is a signal issue then why does the crappy old tach thats hooked up now work but not this brand new one?
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djkeev
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PostPosted: Tue Feb 03, 2015 4:59 am    Post subject: Reply with quote

It would be helpful if you told us a little about your new tach.
Rather than terms of crappy old and new.......

Brand?
Model?

It may have some features designed for newer cars that some may know about.
Some have internal cylinder switches that must be set, there are different wiring methods for attaching to various ignition systems as well.

Dave
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jsmiller
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PostPosted: Tue Feb 03, 2015 5:09 am    Post subject: Reply with quote

New tach is an Autogage 2300 (ATM-2300), old tach (one hooked up now) I haven't a clue? It doesn't even have a name on it!
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djkeev
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PostPosted: Tue Feb 03, 2015 5:14 am    Post subject: Reply with quote

Did you set the cylinder selection switches to 4 cylinder?

Did you verify wiring to the proper locations or just utilized the existing wires from the old tach?

https://www.autometer.com/media/2650-468H.pdf

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jsmiller
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PostPosted: Tue Feb 03, 2015 5:18 am    Post subject: Reply with quote

I've wired it up correctly, and yes the switches are set to the 4cyl position. The needle goes crazy, not just the wrong rpm reading.
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danfromsyr
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PostPosted: Tue Feb 03, 2015 7:02 am    Post subject: Reply with quote

quite possibly your 85+ ECU puts out a different Tach signal than the tach is expecting

old early tachs (VW and other) use a signal from the coil to trigger
new tachs use a signal from the ECU

you likely need a Tach adapter, MSD is likely your best availability in Australia

Link: https://www.google.com/webhp?sourceid=chrome-insta...ch+adapter
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MarkWard
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PostPosted: Tue Feb 03, 2015 9:19 am    Post subject: Reply with quote

I guess we need to know where you are getting your rpm signal from the ECU or directly from the ignition coil.
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jsmiller
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PostPosted: Tue Feb 03, 2015 1:41 pm    Post subject: Reply with quote

I'm getting the signal from the the tach wire that goes to the cluster (pin 14??). But I've also wired it directly to the negative side of the coil and same thing happens!
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crazyvwvanman
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PostPosted: Tue Feb 03, 2015 2:20 pm    Post subject: Reply with quote

The tach wire on the dash cluster 14 pin connector comes from the coil negative side anyway, which is also connected to the ECU since the ECU is what fires the coil. (on USA/CA vans the tach signal is on pin 9 of 14)

There is a known issue with the tach signal on Digifant 2.1 models. The tach made for that works but other tachs often don't. Even the tach from an earlier Digijet can act crazy if hooked to the Digifant. Likewise the factory tach for Digifant models is known to give problems when you are trying to use it with something other than a Digifant.

Mark


jsmiller wrote:
I'm getting the signal from the the tach wire that goes to the cluster (pin 14??). But I've also wired it directly to the negative side of the coil and same thing happens!
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jsmiller
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PostPosted: Tue Feb 03, 2015 3:01 pm    Post subject: Reply with quote

Ok pin 9 then, the green wire, the one the current tach is hooked too.

crazyvwvanman wrote:
There is a known issue with the tach signal on Digifant 2.1 models.


Well I'm thinking this must be the issue, but is there a known fix, or aftermarket tach that can read the signal? While I'd love to put a factory in dash tach in there, I've already got holes drilled in the dash for the tach that's there now. Plus a $60 aftermarket tach is way cheaper than and easier to find than a factory one.
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djkeev
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PostPosted: Tue Feb 03, 2015 3:46 pm    Post subject: Reply with quote

A Manufacturers Web site is often a treasure trove of information......
http://www.autometer.com/resources/index/faq

Click on the link..... Watch the video.......
http://www.autometer.com/resources/index/faq_view/id/51

Image may have been reduced in size. Click image to view fullscreen.


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jsmiller
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PostPosted: Tue Feb 03, 2015 6:31 pm    Post subject: Reply with quote

Thanks for that info Dave, however I don't believe this is and installation issue and is likely related the type of signal from the negative side of the coil specific to Digifant? Most tachometers rely on a 'square' type signal (I.e. on/off pulse from the coil) of which I'm starting to think (based on my research thus far) the Digifant system does not produce for reasons still unclear?

I'm tring to determine:
1. It's the signal from my Digifant coil unreadable by my new tachometer, and if so is there a solution? Different aftermarket tach that will work or some type of signal filter that will fix the issue; or
2. Is my newly purchased (Autogage 2300 tachometer) just broken?

As mentioned previously it appears to be a signal issue, that others have potentially also experienced? If any of you vanagon gurus can clear this up for me that would be much appreciated.
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wcdennis
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PostPosted: Tue Feb 03, 2015 8:09 pm    Post subject: Reply with quote

Is it not worth even trying the resistor fix?
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jsmiller
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PostPosted: Tue Feb 03, 2015 8:26 pm    Post subject: Reply with quote

There's a video on YouTube by a 'mercedesdieselguy' where he had a similar issue when putting a tach in his 91. He did the resistor thing and it was no help? Hey I'd try it no worries just looking for a bit more of a solid confirmation that a fix actually does exist?
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jsmiller
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PostPosted: Wed Feb 04, 2015 3:14 pm    Post subject: Reply with quote

Ok I've heard that putting a diode in line with the signal wire might work? And someone on another forum said they used an 'older' VDO brand tach on their 89 and it worked?

Come on guys, surely there's a answer to this? I thought this would be a no brainer on here? Maybe it's more complicated than I thought?
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crazyvwvanman
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PostPosted: Wed Feb 04, 2015 3:23 pm    Post subject: Reply with quote

Most of our vans here came with tachs, the vast majority have them starting with 1985. Until recently they were easily available second hand at a reasonable price for people who wanted to add one.

Mark

jsmiller wrote:
Ok I've heard that putting a diode in line with the signal wire might work? And someone on another forum said they used an 'older' VDO brand tach on their 89 and it worked?

Come on guys, surely there's a answer to this? I thought this would be a no brainer on here? Maybe it's more complicated than I thought?
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Merian
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PostPosted: Wed Feb 04, 2015 3:29 pm    Post subject: Reply with quote

cars & tachs differ in how they do the pulse counting - e.g Porsche changed their method in the early 1970s

if the resistor doesn't work you might put a scope on the Van's trigger wire and see what it looks like
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jsmiller
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PostPosted: Thu Feb 05, 2015 2:02 am    Post subject: Reply with quote

Well someone suggested putting a diode in line with wire from the coil. So I tried it when i got home from work. It was worth a try I guess. But it didnt work, same issue diode or not?

How can the signal from the negative side of the coil have such a erratic pattern to we're a standard tachometer won't read it and the car still run? I'm starting to get pretty frustrated here. Especially because in sure it's a very simple answer!

Anywoo back to square one.
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djkeev
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PostPosted: Thu Feb 05, 2015 6:50 am    Post subject: Reply with quote

We are all guessing and trying to help but we obviously do not have the answers you need.

I sure would have contacted the manufacturer and see what they say. It may be incompatible, a wiring glitch, a defective unit..... Who knows?

This is really the first thing you should have done is sent off an email or call them.........


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Dave
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http://www.thesamba.com/vw/forum/viewtopic.php?t=392473

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http://www.thesamba.com/vw/forum/viewtopic.php?p=6315537#6315537

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Gauche1968
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PostPosted: Thu Feb 05, 2015 8:40 am    Post subject: Reply with quote

crazyvwvanman wrote:
The tach wire on the dash cluster 14 pin connector comes from the coil negative side anyway, which is also connected to the ECU since the ECU is what fires the coil. (on USA/CA vans the tach signal is on pin 9 of 14)

There is a known issue with the tach signal on Digifant 2.1 models. The tach made for that works but other tachs often don't. Even the tach from an earlier Digijet can act crazy if hooked to the Digifant. Likewise the factory tach for Digifant models is known to give problems when you are trying to use it with something other than a Digifant.

Mark


jsmiller wrote:
I'm getting the signal from the the tach wire that goes to the cluster (pin 14??). But I've also wired it directly to the negative side of the coil and same thing happens!


Using two Digifant tachs on Digijet without any problems....
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