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Old 03-04-2015, 01:11 PM   #1
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Default MSPNP2 tach malfunctioning in 1.6

So I have two cars:

1st: Mine, 1.6, stock CAS, GM coils, no ignitor, tach rads 1/2, lots of throttle cuts the tach off. Does this with TPS plugged/unplugged, and with stock wiring and the alternate tach out pin.

2nd: Project Lazaraus, MSM, NB cam/crank sensors, VVT coils, tach reads correctly, but cuts off with lots of throttle, just goes to zero. Let off and it it'll turn back on at the correct location.


Any ideas? Both have the yellow/blue and black/white wires crimped together from the ignitor, as per the VVT/NB swap instructions.
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Old 03-05-2015, 10:27 AM   #2
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What exactly is driving the tach on both of them?

You may be better off rewiring it to the MSPNP tach output.
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Old 03-05-2015, 11:57 AM   #3
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I did this. I cut the splice at the old igniter location, and the tach died. I then ran the yellow/blue wire to the tach out in my front plug, and it reads half, and shuts off with hard throttle.
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Old 03-05-2015, 12:52 PM   #4
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Did you tie together the black/white and blue/yellow wires? That could be why you are only reading half of the revs.

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Old 03-05-2015, 02:17 PM   #5
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Damn reply keeps being deleted.

I followed your instructions when I wired my toyota cops, then converted it to the GM coils. They're the same, except no coil output, instead power, trigger, and two grounds AFAIK.

I followed Savington's VVT coil wiring instructions for Laz, in the VVT swap megathread.
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Old 03-05-2015, 02:19 PM   #6
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Where does the tach out go on 1.6 mspnp?

Edit: nvm saw its the front plug.
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Old 03-05-2015, 02:31 PM   #7
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Any chance you have the tach output settings on half speed?



Laz's problem sounds like its a weird gremlin, your half speed problem sounds like a setup (wiring, or tune) problem.
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Old 03-05-2015, 02:36 PM   #8
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Did some more digging and ignore my black and white comment, I don't think that is necessary with the GM coils. Fingers crossed its the setting.
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Old 03-05-2015, 02:52 PM   #9
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Goes to the ignitor. Then the ignitor sends the signal to the dash. That's why you need to crimp the two together when you install cops.
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Old 03-05-2015, 02:53 PM   #10
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And no, when enabling the front tach output in, it's running on pin "IGN", and "normal". half speed makes it run at 1/4 speed.
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Old 03-05-2015, 02:57 PM   #11
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Do you have a pull-up resistor on the tach signal, like in the diagnostics box?

MX-5 Miata Forum - View Single Post - [NA] weird tach behavior with megasquirt

Although the megasquirt tach out might not need it.
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Old 03-05-2015, 03:00 PM   #12
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MX-5 Miata Forum - View Single Post - [NA] weird tach behavior with megasquirt

Sounds like the tachout pulls to ground and the later wiring has a pull-up resistor in the wiring. So with no pull-up you could get erratic tach signal.
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Old 03-05-2015, 05:11 PM   #13
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I don't think that's right. I have no pullup, and I did the same blue/yel to black/wht Curly's done. Both of these cars were 1.6's right? Don't you have Laz old motor Aidan?

My setup is on pin TACHOUT though, not IGN. Since the 1.6 doesn't use the ECU to drive the tach in stock trim I had to wire the blue/yellow wire that goes to the ignitor to the MS tachout pin. I am on a DIYPNP though, they can't be that different? Sure sounds like you've already done all this.

My tach still drops out occasionally, like it missed reading a single tach pulse. It thinks it's quickly decelerating, but then snaps right back to normal. I wonder if the early miata tachs just suck?
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Old 03-05-2015, 05:20 PM   #14
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On a 1.6L, if youre using TACHOUT instead of the ignitor:

you can send it to the B/W wire on 2I. This brings the tach signal to the ignitor wiring.

There you must combine b/w and y/b as show above.

This brings the TACHOUT signal from the MS to the y/b wire. This is the wire that goes back to the dash tach.

There should be nothing else connected to the y/b wire--no coils, no 1K pullup in the diagnostics box.


I've seen heard on anyone having issues using tachout from the MS -- your two on these MSPNP2 are the first I've ever heard of.
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Old 03-05-2015, 05:27 PM   #15
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Hmmm, the half tach is still weird.

I assume its correct in tuner studio on both setups right?
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Old 03-05-2015, 05:32 PM   #16
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I think the output pin should be changed from IGN to TACHOUT.

It fires batch, and it's reading off the spark channels so it reads half right?
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Old 03-05-2015, 05:33 PM   #17
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Yes, both tachs in TS work fine no matter what throttle.

let me try changing tach output to TACHOUT and see if anything changes. I'll also recrimp the black/white and yellow/blue wires together, right?
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Old 03-05-2015, 05:35 PM   #18
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If you have the blue/yellow wire connected directly to the ecu then the black/white shouldn't matter.
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Old 03-05-2015, 05:36 PM   #19
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Yeah, the crimping of wires is to keep from having to run a new wire behind the dash so it still needs to be done. The ECU gets a signal from the ignitor in stock form, that's the one between the ECU and ignitor on 2I. The dash reads right off the ignitor though, so that's why we can splice them together and rewire 2I to the tachout pin. Just saves a wire behind the dash, basically.

edit: the wires are super critical, but there's no need to stick any pullups between the tach and the pulse generator of the MS.
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Old 03-05-2015, 05:37 PM   #20
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IGN should be what you're using for one of the spark outputs--selecting that should be causing a conflict error.

you should be using TACHOUT.


unless DIY does something funky, but looking at their 94-95 basemap for the MSPNP2, they use TACHOUT.
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