Gas tachometer to diesel conversion

[beach_creature]

Wow. The contact cleaner is very expensive. I could also try replacing he potentiometer with a new one. Looks like 20K should work.
I’ll explore other options.
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84 Westy
1.9TD AAZ
5spd manual with Locking Peloquin TBD

[?Waldo?]

A can of DeoxIt D5 is <$15 and does an amazing job. I've used it on quite a few electronic items (power window switches, stereo knobs, air flow meters, etc...) with excellent success. It's perfect for cleaning potentiaometers. A can will last me years which makes the cost seemingly insignificant.

[beach_creature]

It’s been a while since playing around with this. I tried the Deoxit but still does the same thing. Idle is 2000 rpm on any position of the pot. If I turn it all the way clockwise (if think) with force, pushing it past where it will stay naturally (It recoils back), then the revs do drop down between 500 - 1000 rpm, but bounces back up to 2000 rpm once the force of rotation on the pot is let off and it recoils back.

Should I replace the pot? I remember I had use the multimeter to test the resistance on the pot and it seemed to be accurate.

Not sure what else to try.

Thanks.

And for reference, I hooked up a programmable vdo taxh and my idle is about 1000 rpm. The tach is large and no good mounting option. I’d like to get the Vanagon tach working.
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84 Westy
1.9TD AAZ
5spd manual with Locking Peloquin TBD

[Gnarlodious]

Did you take it apart and inspect the pot? Sounds like a base pin is cracked at the solder and intermittently contacting. Or the pot is shot. If the former you might fix it by reflowing the solder.
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Vanagon ’83 diesel AAZ w/Giles injection, 5spd 4.57R&P+TBD and a '78 diesel Rabbit

[beach_creature]

I’ll take it apart again when I get a chance. Should I just replace the pot to be sure?
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84 Westy
1.9TD AAZ
5spd manual with Locking Peloquin TBD

[Gnarlodious]

If a terminal is visibly cracked in the solder then that is your prob. But potentiometers can get broken in the sliding contact or the fine wires inside, in which case they are unrepairable. Try to spray electronic solvent inside or even silicone spray is worth a try, while rotating it. Might just clean it out if there’s a bug stuck in there.
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Vanagon ’83 diesel AAZ w/Giles injection, 5spd 4.57R&P+TBD and a '78 diesel Rabbit

[beach_creature]

I had the cluster out so decided to pull the tach and figure it out. Turns out the potentiometer was damaged and not working. I picked up a few 22K pots for $1 at the electronics shop. Soldered a new one in and finnaly have a working tach! Pretty amazing!
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84 Westy
1.9TD AAZ
5spd manual with Locking Peloquin TBD

[?Waldo?]

Red = Keep
White = Remove
Green = Replace/Add

3.3uF cap: 445-8294-ND
10K ohm res: MFR5-10KFI
0.047uF cap: 399-C410C473K5R5TA-ND
71.5 ohm res: MFR-25FBF52-71R5
0.01uF cap: CS14-F2GA103MYGKA
15K ohm res: MBA02040C1502FRP00

[MarkWard]

[chrismsnt]

This is driving me nuts but where the HECK is the W terminal on the alternator??!!! In my pic below, I thought it's where the green wire was going but that's only a nut to hold on the back plastic housing. Thoughts?

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Chris
1989 T3 Vanagon 16" Syncro
1967 Squareback
https://vwvandiesel.com
Instagram @VW_VanDiesel

[Gnarlodious]

Reports are that the 2-pin socket on the upper right has a tachometer output. If not, you may need to remove the plastic backing and tap into one of the stators. The process is described here:
http://vwdiesel.net/forum/index.php/topic,34707.0.html
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Vanagon ’83 diesel AAZ w/Giles injection, 5spd 4.57R&P+TBD and a '78 diesel Rabbit

[chrismsnt]

[Achilles3588]

I've just done this mod using the parts from Digikey as listed above (with thanks) by Gnarlodious to a gasser tach PCB.

Initially I got no readout. I went back and checked the continuity on the circuits on the reverse side of the PCB node by node and everything checked out OK. In the process of doing that I realized I had installed the D1 replacement bridge in the wrong location!

Removed and reinstalled the link in the correct place, reinstalled the tach in the rig and sure enough it worked! One tweek of the potentiometer and the readout was accurate, too! Fantastic!
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Larry V.~
'91 Syncro Doka 1.9L TDI 'AFN'

[VanTransylvania]

hi there,

thank you for the useful information from this thread. Unfortunately, the result in converting to fit a diesel (jx) engine has been frustrating me for the past week.
here is a video that shows what the rev counter does after double and triple-checking each and every resistor and capacitor. I've also checked them with a multimeter to make sure they meet the above mentioned criteria.

Video >> https://youtu.be/dhN51G8pvok

I also checked the the wire (+ - and W) all good. The alternator has a W by default, i didn't have to change anything.

I am at my wits end and was hoping someone could point me in the right direction.

Thank you in advance for any helpful info.

[?Waldo?]

Where does the needle go when you shut it off?

[VanTransylvania]

when i shut it off, it goes to 0

[?Waldo?]

Did the tach work properly as a gas tach prior to attempting the conversion?

Do you have the polarity backwards on the 3.3uF Cap?

What happens when you adjust the potentiometer?

[VanTransylvania]

when i accelerated (as seen in the video) it shouldn't have gone that high up, from 5k rpm to above 6k rpm, the acceleration should have measured around 1.5k rpm

[?Waldo?]

I saw the video.

Answering the specific questions I asked might help the diagnosis.

[VanTransylvania]

Did the tach work properly as a gas tach prior to attempting the conversion?
- As far as i know, it worked well

Do you have the polarity backwards on the 3.3uF Cap?
- I checked and made sure the polarity on this cap is as it should be

What happens when you adjust the potentiometer?

- nothing happens, i even checked the potentiometer with a multimeter and it works