# 1.8t megasquirt v2.6 tach output issue



## canadiansyncro (Feb 10, 2013)

I have a 1.8t running megasquirt v2.6 
I can't get my factory mk3 tach to play nice with the MS. I've traced the wiring and it all appears to be wired properly. but since I know nothing about circuit boards and was away for work when the board was built, I am at a complete loss as to where to start looking for the cause of my issue. The tach works in tunerstudio, and the car has been dyno tuned so I'm assuming the issue has to be between the board and the stock cluster. I have googled, searched through this forum, and tried asking the friend who built the board and have come up with nothing, past mention of a circuit that needs to be built into the MS unit to make the factory tach play nice with the megasquirt. I am either retarded or blind because I can't find the link to the previously mentioned circuit. At this point any help would be greatly appreciated


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## need_a_VR6 (May 19, 1999)

The circuit to drive the MK3 tach is about the simplest that there is. A few things I need to actually answer your question, as v2.6 isn't a version of anything:

What is your mainboard version (v1.x, v2.2, v3, v3.57, Microsquirt v?, MS3-Pro)?

What is your processor (MS1, 2, 3)?

What modifications have been done to the board so far to enable the tach to work (transistors, jumpers, etc)?

Where does the tach output from the MS land on the stock cluster/fuseblock?


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## canadiansyncro (Feb 10, 2013)

I believe it's a 3.57 main board with ms2 processor. As far as what modifications have been done to the board I have no idea. The only modification I know of is it has everything for launch control built in and boost control was supposed to be built in later but isn't there yet

The tach signal from the megasquirt is wired into the factory spot for the tach signal from the ecu plug g1 pin 12


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## need_a_VR6 (May 19, 1999)

There's no dedicated tach output with that setup, everything is optional and will depend on things that are or aren't installed on the board. Where in your harness does the tach output come from?

v2.6 is an original B&G code version, so I don't know much at all about what is/isn't an option. Generally though if you're not using the stepper idle you can wire either JS0 or JS2 directly to a spare pin to drive the tach, as long as JS9 to 12v jumper is present. You then just need to assign JS0 or JS2 to the tach out feature. Again, I am unsure if this option is available in the B&G code.

Consider using extra: msextra.com


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## canadiansyncro (Feb 10, 2013)

If I open the case for my ecu and take a few pictures would that help? I know absolutely nothing about the inside of this thing for all I know it works because of some magic smoke inside. 

According to the writing on the board it's a v3.0 board. And the 2.6 number came from what tuner studio says. And after looking again that might be the version of tuner studio I have


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## need_a_VR6 (May 19, 1999)

Yes, but you probably have to remove the entire case as many jumpers are easier to do on the bottom. Easiest to leave the 37 pin end of the case connected and remove the 9pin's hex screws and pull the board out the 37pin end.

2.6 could either be that or the B&G code version. If you have a msq or a screen shot of what TS says it could help too.


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## canadiansyncro (Feb 10, 2013)

if it helps I could include my msq file


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## need_a_VR6 (May 19, 1999)

Looks like you only have outputs wired for the coils. If you aren't using FIDLE for anything, that's a viable circuit to use for the stock tach. There will be a menu that is labeled Tach Output, 

Judging by the menu you have, that's an /extra code version of some kind.

You could easily jumper JS0 or JS2 to the IAC1A pin and run the tach from pin 25. Just make sure you also add JS9 to S12C to power that output.


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## canadiansyncro (Feb 10, 2013)

FIdle? i'm assuming that is fast idle for cold start?
I traced for continuity from the fusebox to the db37 connector and found that pin 28 is wired to the factory tach input. My question now is how do I verify that there isn't another circuit using this pin, and then how do I connect the tach circuit I am about to build to this pin?


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## need_a_VR6 (May 19, 1999)

Pin 28 on the MS is 12v switched power to the controller. If you're wired to that the tach won't do anything at all. Double check you're right there though, it wouldn't make any sense to hook it up there.

Pins 25, 27. 29 are all open (IAC1A,1B,2A on the board bottom) to jumper to for tach following my instructions above.


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## canadiansyncro (Feb 10, 2013)

i double and triple check continuity and came up with pin 29 instead of pin 28 what location is that? IAC2A? that spot is open so i'm guessing the guy who built my ecu was in such a rush to get my car done that he didn't bother building the circuit
Thank you need_a_vr6 for all your help. I should be able to make this work by the end of the day


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## canadiansyncro (Feb 10, 2013)

Does it matter if I run the circuit from js0 to iac2a? Or would I need to use js2 for iac2a? I ask because I plugged js2 with solder and my desoldering tool won't suck the solder out


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## need_a_VR6 (May 19, 1999)

Mix and match as you wish. 29 is iac2a, jumper that to js0 and set that to tach in software. Done. 


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## canadiansyncro (Feb 10, 2013)

So circuit is installed, I put everything back together and I still have no tach. Tach output is set to iac2 does it need to be set to iac2a or did I screw up the circuit?


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## need_a_VR6 (May 19, 1999)

If you used js0 use output iac1


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