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Old 03-14-2010, 01:46 AM   #1
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Thumbs up MS installed, No more dashboard tach

Alright so this is my first experience with Megasquirt here. If anyone has any ideas or possible solutions to my problem I would greatly appreciate the advice.

I recently purchased a standalone MS setup from Braineack. After I completed the install, I started up the car and the tach on the dashboard does not work.
Megasquirt sees a tach signal, as the car runs.

The car: 1995.5 Miata - 3 wires go into ignitor
The Megasquirt: 95 standalone Brain built DIY MS 1 v 3.0

What I have tried so far:
Setting Tach Output to "JS0" and Pin10
Jumper from B+ and IG- in diagnostic box, with 1k 1/4 watt resistor

Last edited by hellothere; 03-14-2010 at 07:06 PM. Reason: The unit is a ms 1 v 3.0, with 1k 1/4 watt resistor. Retarded info my bad.
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Old 03-14-2010, 12:31 PM   #2
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1: Jumpering B+ to IG- with no resistor in between is bad. High probability of frying something with that move. What this is doing is putting 12 volts with no current limit at all onto a circuit that's giving closures to ground.

2: When you say "4 wires go into ignitor" does this mean that each of the two ignition coils has four wires going into it?
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Old 03-14-2010, 02:30 PM   #3
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Joe: I did jump the 2 points with a resistor I left that part out on my post.

There is a plug that goes into the ignitor and it has 4 wires on the plug.

Is it possible that the tach output is just going to the wrong wire?
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Old 03-14-2010, 03:34 PM   #4
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I did not build the tach output circuit for him and I've never had the for the circuit with a 94-95 standalone MS before. So please, no more responses about a wire in the wrong spot or the circuit built incorrectly...

I have a feeling he has a 95.5 that does need the circuit as the coils don't send the tach signal back to the dash.
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Old 03-14-2010, 03:43 PM   #5
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You did build mine for my 94 standalone, and I did have to move a wire. I also had to solder the MAP sensor to the main circuit board when I discovered that it had been overlooked.
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Old 03-14-2010, 05:56 PM   #6
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Unless you were the only other person with the no tach issue on a 94-95 that I've built, no one else has told me about the issue
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Old 03-14-2010, 06:08 PM   #7
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I didn't know there such hint as a 95.5 so I'm subcribing
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Old 03-14-2010, 06:33 PM   #8
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Quote:
Originally Posted by Braineack View Post
Unless you were the only other person with the no tach issue on a 94-95 that I've built, no one else has told me about the issue

I have a 94, and my tach does not work in my dash either. But, I have been too lazy/busy to try to sort it out. LINK
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Old 03-14-2010, 06:48 PM   #9
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well crap...looks like I need to build the tach output circuit for you guys then...probably like 20 of you driving around without tachs... sigh
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Old 03-14-2010, 07:06 PM   #10
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Big dumb mistake on my part! The connectors I looked at weren't actually going into the coils. The plugs going into the coils have 3 wires.
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Old 03-14-2010, 09:53 PM   #11
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I just installed the basic pullup mods, Joe's spark mod, and installed a 1K resistor between +12v and 2I for my 94 standalone. Dash tach works great...

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Last edited by Cococarbine3; 03-14-2010 at 10:11 PM.
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Old 03-14-2010, 10:29 PM   #12
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Quote:
Originally Posted by Cococarbine3 View Post
I just installed the basic pullup mods, Joe's spark mod, and installed a 1K resistor between +12v and 2I for my 94 standalone. Dash tach works great...
If you have a 1.6, or an early 1.8 (up to mid-95) where each coil has four wires, then all you need is a resistor to pull up the tach line, and the coils will drive it.

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Originally Posted by hellothere View Post
Big dumb mistake on my part! The connectors I looked at weren't actually going into the coils. The plugs going into the coils have 3 wires.
Late '95 and onwards needs a dedicated circuit inside the MS to drive the tach. The coils aren't part of the equation.

It's not complicated to do:



The line that says "to tacho" goes to the wire on your ECU connector that drives the tach. On a '95.5, this is B/W at 2I.

The line that says "MS PCB" goes to whatever pin has been selected in software to drive the tach:




Moar: MSnS-Extra Hardware Manual
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Old 03-14-2010, 11:00 PM   #13
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That's what I thought, thanks for confirming. Seems he has a 95.5 that needs the circuit and I'll gladly build it for him and anyone who needs it that I build a 95 MS for.

Buffon needs to jump his diagnostics box as he's confirmed 4 fours wires in his coil connectors.
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Old 03-15-2010, 02:23 AM   #14
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I don't remember my fix exactly, I thought it was just a wire change, but I found a pack of resistors with my soldering iron this afternoon, so I may have inserted a resistor too. It wasn't a big deal (nor was the map sensor), that's why I never brought it up.
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Old 03-15-2010, 10:46 AM   #15
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Quote:
Originally Posted by 94mx5red View Post
I have a 94, and my tach does not work in my dash either. But, I have been too lazy/busy to try to sort it out. LINK
Then you need to run to radioshack and buy a pack of 1/4 watt 1Kohm resistors for .99c. Then jump IG- and B+ with one in your diagnostics box. This pull-up so power the tach signal yet again and your dash will come to life.

Quote:
Originally Posted by boileralum View Post
I don't remember my fix exactly, I thought it was just a wire change, but I found a pack of resistors with my soldering iron this afternoon, so I may have inserted a resistor too. It wasn't a big deal (nor was the map sensor), that's why I never brought it up.
The map sensor thing is all on me. It's usually the last thing I put on the board and that must have slipped my mind after fitting.

I think from this point on I'll just build the tach circuit for every 94-97 MS I build, it's easier for me to just add the extra circuit and wire in the harness from the get-go without the need for you guys to have to do anything extra on your end when installing or falling to check if you're a 95.5 and ending up in a situation like hellothere.
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Old 03-15-2010, 01:44 PM   #16
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Like I said, it was no biggie. You saved me a lot of time and trouble doing the assembly, I still got to do a little hands-on for the build, and all is kosher.
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Old 03-15-2010, 02:07 PM   #17
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...Why I was not previously able to figure out that 'tacho output pin' has something to do with the tach is beyond me.

Mine is set to OFF.

Scott, which selection should I try? I do not have my laptop with my, but I think 'X2' is the fans (which is another story), and I think the rest may be unused.
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Old 03-15-2010, 02:09 PM   #18
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no selection, you need to go grab a 1K 1/4 watt resistor and jump IG- and B+ plus in the diagnostic box with it. That should solve it. I used to build the pull up resistor into the harnesses, then found it was easier having people jump the signal and provided a resistor to use...and then it simply slipped my mind.
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Old 03-15-2010, 02:25 PM   #19
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Quote:
Originally Posted by 94mx5red View Post
...Why I was not previously able to figure out that 'tacho output pin' has something to do with the tach is beyond me.
To Braineack you listen.

Tach Output from the MS is only needed for folks with '95.5 and later three-wire coils. Anybody with a 1.6, or with a 1.8 with four-wire coils, can just pullup the stock tach wire which goes to the ignition system and let the coils do the work.
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Old 03-15-2010, 04:39 PM   #20
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Good stuff. I will try to make a run to radio shack sometime soon.
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