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

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?

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?

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.

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.

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 :vash:

I didn't know there such hint as a 95.5 so I'm subcribing

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

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

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. :facepalm:

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...

Attachment 199414

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.

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:

http://msextra.com/doc/ms1extra/MS_E.../LowVTacho.GIF

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:

http://img38.imagefra.me/img/img38/2...xm_5dac91e.gif


Moar: MSnS-Extra Hardware Manual

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.

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.

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.

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.

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.

:hsugh:...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.

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.

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.

Good stuff. I will try to make a run to radio shack sometime soon.