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Gas Tacho / Revcounter Conversion to Diesel W terminal
RabbitGTDguy:
Another SUCCESS for this FAQ. I was able to convert an early Mk1 (round) VDO tachometer to W terminal with success in the last couple of days. I was even able to easily calibrate it on the b3 16v's 90amp alternator as it has an active W terminal.
No fluctuations and very little adjustment. All adjustment was able to be done at the potentiometer itself...
Good stuff...maybe I'll post a picture of the modified board here in the next few days. My soldering skills are rusty, but getting better I guess...some pretty creative wrapping and and installation a few components in a series.
Also, I did not install the 3.3uF inline of the tacho output wires... haven't seen any problems as of yet.
Joe
X@V:
Could someone help me please? I need to know what to do for this:
http://www.vwdiesel.net/phpBB/viewtopic.php?t=11404
RabbitGTDguy:
More Proof!!! Posted in my thread as well...but this is good here too!!!
Finally, got a chance to start up the mTDI Rabbit again here today. After fixing the dowpipe, etc. etc. and getting the exhaust hooked back together all is well. Just hadn't had the time
Also, I was able to full intergrate the tach into the early dash, I even used the factory german cluster plug and was able to change out the connections needed for a "factory" hookup and look so that I didn't have to tape off terminals, add connections, etc. The early MK1 cluster plugs are actually really nice to work with, They come apart EASY which makes swapping connections really easy as well. I ended up switching to the motormeter circuit sheet that I had as the VDO one was pretty bad. After comparing them though I didn't see any major differences, etc. and everything is good to go!
Idles a bit high. at about 1.5k and I don' t think the engine is actually idling that high so I think that accounts for the difference in between the pulleys on the test/calibration car (my 16v b3 gasser ) and the mTDI engine running serp belts and the 2.0 90amp alternator.
Easy enough to fix though...
Here are a few pics...as promised...
Had that second one revved quite a bit higher...but my digi cam recycle time SUCKS.... either way. No flutter, etc. I'm going to need to find another "VDO" parts tach for a good needle (as this ones paint is damaged and/or do something with the needles. The biggest drawback I think with the older gauges is the illumination itself...
Hmm...maybe an LED project in the future!!!
Either way...WORKING CONVERTED GASSER TACH!!! WAHOO!!!
Joe
coalminer16:
I just got two tachs wired up for both of my rabbits and neither of them are the correct rpm. They both idle at 2000 rpm. Any pointers I used the correct resistors. I may have the wrong caps in the system (due to converting). Would this be the problem or do I just need to get a variable resistor. Can I put the variable resistor on the input line if that is the only way to correct it. Any suggestions let me know please. I did everything exact but the optional caps on the two wires going to the needle. Maybe I need a higher resistor value somewhere. Doesn't jump around though (the needle). Thanks
coalminer16:
I posted that a 5.6 k resistor makes the rpm correct at start up but changes by about half if I drive interstate speed. I don't think it does it in town but I haven't driven it long enough to know. I asked my Electrical Engineering friend/previous teacher and he said that it might have a "cold connection" is what I think he put it as (I am Mechanical Engineering so he has the better understanding on this part). He explained that as a person solders the resistors and caps on, if the ends of the wire moves before total cool down of the solder then it won't have a perfect connection. So after a while the connection will heat up because of this and the resistance of the solder actually changes. Long story short he said if you can get the metal flowing really good and have the wire end in the pool of metal and then take the heat source off and not drag it off (in a sweep motion, like welding with wire or arc almost) then it will prevent some of the cold connections. But because this is a small circuit board that is the old style with solder connections this will be hard anyways. Bottom line I have something that if I factor if the engine is warm or cold I know roughly the rpm and it looks nice and factory installed looking. Plus now I can see the temp gauge better if I am leaning forward on the steering wheel on some of those long drives (not uncommon I drive 24 hr strait-Spring break, SD to Vancouver to Mexico and back in 9 days with 4 days skiing). Hope this helps.
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