# MS using VR sensor running distributorless-can a stock MKII tach be used? Searched...



## evil-e (Aug 15, 2005)

*Found the answer myself. See post below about 1K 1watt resistors and ditching the zener diode altogether.*

Can a stock MKII tach. be used when using an ABA block w/ stock VR sensor while running distrubutorless? I searched this a couple of different ways and came up empty handed. All I found were people trying to figure out a way to use the stock tach with MS using a distributor. I really don't want to have to get an aftermarket tach. Anyone know if there's a way to do this?


_Modified by evil-e at 10:35 AM 6-15-2007_


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## patatron (Aug 10, 2003)

*Re: MS using VR sensor running distributorless-can a stock MKII tach be used? Searched... (evil-e)*

Yes it can, I will include the parts for free with your order due to the delay. -Pat


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## evil-e (Aug 15, 2005)

*Re: MS using VR sensor running distributorless-can a stock MKII tach be used? Searched... (patatron)*

Thanks Pat!


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## evil-e (Aug 15, 2005)

*Re: MS using VR sensor running distributorless-can a stock MKII tach be used? Searched... (patatron)*


_Quote, originally posted by *patatron* »_Yes it can, I will include the parts for free with your order due to the delay. -Pat

Pat,
Is there another package coming??? I only got the ecu and the disk.
Sent you an IM and an email. Please get back to me ASAP.


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## evil-e (Aug 15, 2005)

*Re: MS using VR sensor running distributorless-can a stock MKII tach be used? Searched... (evil-e)*

bumping this back up.
Have the Megasquirt upand running and installed the resistors/diodes as per pat's instructions, but I'm still not getting a tach reading on the factory tach. Anyone else know how any info on running a stock tach for a CE2 cluster on a wasted spark MS setup????


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## need_a_VR6 (May 19, 1999)

*Re: MS using VR sensor running distributorless-can a stock MKII tach be used? Searched... (evil-e)*

A normal MS tach driver circuit will NOT work with a stock tach. There was a good tip about using a relay coil to give the high frequency pulses to a stock tach but I can't find it at the moment. You can also use the setup that's in the msextra manual under tach circuit, the one that comes off the coil primaries with the diodes will work as I've done similar on Mk2 VR6's with the stock tach.


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## eurotrashrabbit (Oct 25, 2001)

*Re: MS using VR sensor running distributorless-can a stock MKII tach be used? Searched... (evil-e)*

It works on early Mk1 clusters mine plugged right in and worked with EDIS from the tachsignal wire off the control module to the red with a black tracer going to the original coil wire


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## need_a_VR6 (May 19, 1999)

*Re: MS using VR sensor running distributorless-can a stock MKII ... (eurotrashrabbit)*

That's because the EDIS tach wire isn't a square wave output like MS is.


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## evil-e (Aug 15, 2005)

*Re: MS using VR sensor running distributorless-can a stock MKII tach ... (need_a_VR6)*


_Quote, originally posted by *need_a_VR6* »_A normal MS tach driver circuit will NOT work with a stock tach. There was a good tip about using a relay coil to give the high frequency pulses to a stock tach but I can't find it at the moment. You can also use the setup that's in the msextra manual under tach circuit, the one that comes off the coil primaries with the diodes will work as I've done similar on Mk2 VR6's with the stock tach.

That's the setup I'm trying to run, but I guess it's possible I didn't tap into the right wire @ the fuse box. Maybe I should just tap right into the green (I think) wire off the cluster???


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## need_a_VR6 (May 19, 1999)

*Re: MS using VR sensor running distributorless-can a stock MKII tach ... (evil-e)*

Green/Black on a CE car I think.


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## evil-e (Aug 15, 2005)

*Re: MS using VR sensor running distributorless-can a stock MKII tach ... (need_a_VR6)*

I'll give it a try.


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## evil-e (Aug 15, 2005)

*Re: MS using VR sensor running distributorless-can a stock MKII tach ... (evil-e)*

edited w/ correct info on the orange zener diode.
Figured out what the deal was. I was following the instructions on Patatron.com's forums for the wiring of the diodes as per this diagram:









The black diodes in the diagram are all facing the wrong way.
Current only can flow from the anode to cathode on a diode.
The end with the band is the cathode and no matter what wire
you try to tap into to get a tach signal, you're not going to get
one if the diodes aren't allowing the signal to get through.
Thanks to need_a_VR6 for the info on the zener diode (orange) is facing the correct way. Only the black diodes are facing the wrong way








Just a heads up to anyone in the future trying to get a waste spark tach signal on their MS.

_Modified by evil-e at 9:30 AM 6-3-2007_


_Modified by evil-e at 9:33 AM 6-3-2007_


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## need_a_VR6 (May 19, 1999)

*Re: MS using VR sensor running distributorless-can a stock MKII tach ... (evil-e)*

Woah that's wrong! JUST the black ones (1N4001) are backwards. The orange (zener) diode has have the stripe facing the coil outputs. It works like a voltage clamp so the clutster doesn't see funky spikes. Don't reverse them all it can blow your tach.


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## evil-e (Aug 15, 2005)

*Re: MS using VR sensor running distributorless-can a stock MKII tach ... (need_a_VR6)*

OK, so just the black diodes are backwards then?


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## need_a_VR6 (May 19, 1999)

*Re: MS using VR sensor running distributorless-can a stock MKII tach ... (evil-e)*

Yes. The single zener is there to act as a filter of sorts.


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## evil-e (Aug 15, 2005)

*Re: MS using VR sensor running distributorless-can a stock MKII tach ... (need_a_VR6)*

Thanks for the info. http://****************.com/smile/emthup.gif 
edited post w/ correct info about the zener diode.


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## evil-e (Aug 15, 2005)

*Re: MS using VR sensor running distributorless-can a stock MKII tach ... (need_a_VR6)*

Anyone know the digi-key part numbers for the black diodes in the diagram and the orange zener diode as well? I'd like to order them directly from digi-key or try and find their equivalent locally.


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## DieGTi (Jun 19, 2001)

*Re: MS using VR sensor running distributorless-can a stock MKII tach ... (evil-e)*

1n4004 is a nte116 (black & grey)
1n5325b or 1n5355b (orange) is a "can't remember at the moment"


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## evil-e (Aug 15, 2005)

*Re: MS using VR sensor running distributorless-can a stock MKII tach ... (DieGTi)*

Well I *finally* have this figured out. 
Ditch the wiring diagram above and use the following setup.
Off each of the coil trigger wires coming from the ecu to the coil pack run a 1K 1 watt resistor into a IN4005 diode (both pieces available from Radio Shack for under $5.00). 
After the cathodes, bridge the ends of diodes together and solder onto a regular wire and run that right to the MKII tach.
You now have a working tach.
You don't need the zener diode (orange stripe) and I'm sure it would work with the IN4006 diodes as well if you've already got them.
I found this info on an 034efi.com forum regarding their wasted spark coil setup in a MKII, so thanks to them for sure.


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## mattkosem (Apr 29, 2004)

*Re: MS using VR sensor running distributorless-can a stock MKII tach ... (evil-e)*

Would this be appropriate for MKI tachs too?
--Matt


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## evil-e (Aug 15, 2005)

*Re: MS using VR sensor running distributorless-can a stock MKII tach ... (mattkosem)*


_Quote, originally posted by *mattkosem* »_Would this be appropriate for MKI tachs too?
--Matt

I'm not 100% sure on this, but I think I read something about the MKI tachs working better off non-oem tach signals.
*Update.*
Also, I hadn't driven the car yesterday morning when I got the resistors and diodes soldered in and the tach signal appeared to be spot on. On my drive home after work, I did however notice that the tach was bouncing around slightly. I'm going to try using the IN4006 diodes in place of the IN4005's since they are rated for a higher voltage range. Also, that is what was recommended on the 034 efi forum, I just couldn't find any of the 4006's at my local Radio Shack.
The tach signal is smooth upon acceleration, but when you're driving at a steady speed/rpm the tach starts to bounce a little bit.
I verified that the tach and the VR sensor are reading the same rpm through MegaTune while driving though.


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## steve12345 (Jan 8, 2006)

*Re: MS using VR sensor running distributorless-can a stock MKII tach ... (evil-e)*

Did you ever get the tach to work smoothly? 
I am about to wire up my tach to my wasted spark Megasquirt, and was planning to use this guide.


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## evil-e (Aug 15, 2005)

*Re: MS using VR sensor running distributorless-can a stock MKII tach ... (steve12345)*

At idle and up to around 3-4K it works smoothly. It does jump around at times. I was going to get some different diodes and try it again, but it works pretty good right now so I haven't messed with it much.
Here's a pic I borrowed from the 034efi forum thread on this:








Good luck with it, and btw, this setup is meant for a wasted spark system.


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## steve12345 (Jan 8, 2006)

*Re: MS using VR sensor running distributorless-can a stock MKII tach ... (evil-e)*

I did this, including the zener diode. Works great. I noticed that my tach reads a bit higher than the tach in megatune. MS says 3000. Tach says 3200. Might be calibration of the gauge. I also noticed that I pick up some RF interference on my radio at certain RPMs. I noticed around 4k today.
I used 1N4001 as they are good for up to 50V. Can't recall the zener part number. And used the 1k 1w resistors. All were in stock at Radio Shack for a few bucks.
Thanks for the pics! http://****************.com/smile/emthup.gif










_Modified by steve12345 at 11:13 PM 12-7-2007_


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## evil-e (Aug 15, 2005)

*Re: MS using VR sensor running distributorless-can a stock MKII tach ... (steve12345)*


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## chrisbmx68 (Aug 14, 2003)

*Re: MS using VR sensor running distributorless-can a stock MKII tach ... (steve12345)*


_Quote, originally posted by *steve12345* »_I did this, including the zener diode. Works great. I noticed that my tach reads a bit higher than the tach in megatune. MS says 3000. Tach says 3200. Might be calibration of the gauge. I also noticed that I pick up some RF interference on my radio at certain RPMs. I noticed around 4k today.
I used 1N4001 as they are good for up to 50V. Can't recall the zener part number. And used the 1k 1w resistors. All were in stock at Radio Shack for a few bucks.
Thanks for the pics! http://****************.com/smile/emthup.gif









_Modified by steve12345 at 11:13 PM 12-7-2007_

just using megasquirt and a dizzy the tach reads about 200rpm higher than the computer tells me I think you are correct in assuming that is a gauge calibration issue.


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