Jumpy Rev Counter/Tach

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evan.fraser.274
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Jumpy Rev Counter/Tach

Post by evan.fraser.274 »

I have a VDO tacho for my T3 that I installed. Problem is it jumps wildly while the engine is running. The feed is off a coil-less electronic ignition module that the guys from VDubTech installed (one of the designated outputs is supposed to feed a standard tacho that is normally connected to a coil). Any advise anyone could offer on how I can get it to calm down would be most welcome!


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Re: Jumpy Rev Counter/Tach

Post by Wentzel »

Hi I don't know if it is relevant to your electronic system. My tacho jumped and I found that the wire from coil to tacho had an break in the insulation that touched ground as the engine was running. You could check for any bad connections or broken insulation on the wire.
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Re: Jumpy Rev Counter/Tach

Post by FaanP »

evan.fraser.274 wrote: ↑Fri Jul 07, 2017 2:37 pm I have a VDO tacho for my T3 that I installed. Problem is it jumps wildly while the engine is running. The feed is off a coil-less electronic ignition module that the guys from VDubTech installed (one of the designated outputs is supposed to feed a standard tacho that is normally connected to a coil). Any advise anyone could offer on how I can get it to calm down would be most welcome!
You need to install a diode on the signal - I think .... let me google a bit and get the correct info for you :D

Here you go: Be sure and put a diode on the 'input pulse' wire to the tach! White stripe on diode towards the tach. 1N4000 up It will 'smooth' the needle
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Re: Jumpy Rev Counter/Tach

Post by sean »

FaanP wrote: ↑Fri Jul 07, 2017 3:34 pm
evan.fraser.274 wrote: ↑Fri Jul 07, 2017 2:37 pm I have a VDO tacho for my T3 that I installed. Problem is it jumps wildly while the engine is running. The feed is off a coil-less electronic ignition module that the guys from VDubTech installed (one of the designated outputs is supposed to feed a standard tacho that is normally connected to a coil). Any advise anyone could offer on how I can get it to calm down would be most welcome!
You need to install a diode on the signal - I think .... let me google a bit and get the correct info for you :D

Here you go: Be sure and put a diode on the 'input pulse' wire to the tach! White stripe on diode towards the tach. 1N4000 up It will 'smooth' the needle
This is 100% correct. I have had the exact same problems a number of times. The diode solves the problem.
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evan.fraser.274
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Re: Jumpy Rev Counter/Tach

Post by evan.fraser.274 »

Thanks Sean/Faan...I will get one this morning and give it a try!!
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