Braineack built MS (originally made for a 1.6). Parallel install (for now).

Finally got it installed and the car idling but my tach on the cluster isn't working. From searching I figured out I have a 3 wire coil pack and thus a 95.5 and will probably need a tach driver circuit.

Does this get built in the proto area? Anybody have pics of their board? How does it get wired to the DB37 / harness? Do I need to run a wire from my guage cluster to the MS?

Also I have a constantly illuminated CEL since installing the MS. I'm not using a MAF and I ran wires directly from the AIT to the factory harness. Any ideas? I haven't really researched the CEL yet....

 

if parallel, the stock ECU should still be providing the tach output...

read what the CEL is, even when using the GM AIT, if it's going back to the stock ECU it should be happy enough not to throw a CEL from it.

 

Crap...so I need to look at my harness? I'm tempted to send the whole thing to you for a once over, but I really want to drive this damned car....

I was also wondering, Shouldn't the stock ECU control idle? At first, my AIT wasn't hooked up and it ran like crap until I fixed the connection. Also the idle hunts badly when the fans come on. You built it as a parallel but with the fans mod. Am I still able to allow the stock ECU to control that or do I have to control fans with the MS since it has that mod?

 

What about that resistor in the diagnostic box?

 

I don't think that works for the 3 wire coil cars, IIRC.

 

Check to see if there's a wire on 2I, that should be your tach out wire. it should be going straight from the ECU to the harness and the MS won't be touching it.

 

Thx. I'll give it a look when I get home tonight.

 

So I checked the fault code and it looks like 29-EGR solenoid valve (vent). Likely not relevant to the tach issue.

Yes, there is a wire at 2I and it goes straight to the ECU. Sooo, Whiskey Tango Foxtrot....?

 

Are we sure it's 2I? The more I think about it, the more this makes no sense....

 

pretty damn sure. If you can test, it should go all the wya back to the diagnostics box to IG-

 

OK, Google just found this for me, even though I never saw it when searching this site.

https://www.miataturbo.net/megasquirt-18/mspnp-installed-what-happened-my-tach-18670/

Looks like it might be on 1F on the 95.5 cars. Still not clear on the solution though.

 

well there you go, check 1F. I remembered it the opposite way.

 

Cool. Unfortunately I'm not gonna even have time to look at it again until Saturday... :-(

 

So, assuming my harness has nothing on 1F, I will just need to install one on my harness to the 1F spot I assume?

 

yeah, you'd need to make sure it goes across the harness to the ECU. spot will be empty on the oem wiring side otherwise.

 

Thanks Scott!

 

Running the IAT through the stock MAF plug and leaving the MAF unhooked will throw a constant CEL if you're parallel, on 1.8 cars anyway. It bothered me so I cut the wire to the CEL in my adapter harness. On a 94 it's 1C (yel/blk) but double-check for yours.

If you want the CEL to come on with ignition and cranking then go off during run (say, to satisfy a state inspection requirement) then you can jump two wires on a connector behind the glove box. FM has the instructions for this buried within the Link tuning manual .pdf on their site. Recent thread about it here: https://www.miataturbo.net/megasquirt-18/cel-circuit-58696/

 

I ran the IAT back to the harness at the ECU. Should I still get the CEL?

 

Moved that wire and voila! Tacho!

Now my LC1 is suddenly being a *****.....