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Old 08-13-2009, 05:52 PM   #1
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Default toyota cops tach output pin

Does anyone know what that 3rd pin outputs as a signal on the yota cops? I wired in cops but have no rpm signal since it was taken before directly from the -ve of the coil.

I don't have a scope to probe the cops output.
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Old 08-13-2009, 09:23 PM   #2
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Old 08-14-2009, 09:24 AM   #3
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Thanks for the pic.

where do pins 4 and 5 of the miata igniter go? Are these the -ve of the coils?

Anyone has a schematic of the stock ignition system of the miata?
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Old 08-14-2009, 10:00 AM   #4
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Quote:
Originally Posted by 323driver View Post
where do pins 4 and 5 of the miata igniter go? Are these the -ve of the coils?
Assuming you're numbering from 1 at the top, in the original scheme, they are:

1: Coil 1/4 (-) (white) this is the actual coil primary ground side. Unused with COP.
2: Coil 1/4 trigger (brn/yel) this is the +5 trigger from the ECU to the igniter.
3: +12v (blue) This comes from the IG1 position of the keyswitch
4: Tach (yel/blue) drives the tacho in the dash and also goes to the diag conn.
5: IGf (black/white) This is the ignition event confirm that drives the stock ECU. Not needed if you're running MS or similar.
6: Ground (black)
7: Coil 2/3 trigger (brown) this is the +5 trigger from the ECU to the igniter.
8: Coil 2/3 (-) (red) this is the actual coil primary ground side. Unused with COP.

(Note that Mazda calls them A-H rather than 1-8)

Quote:
Anyone has a schematic of the stock ignition system of the miata?
This is from a '90-'93 car:

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Old 08-14-2009, 01:00 PM   #5
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Thank you Joe for the details.

Hmmm, it will be more tricky than I though. On my car, which is a protege AWD, there is only 1 coil and the tach signal goes directly from the coil -ve to the dash counter and the coil is discharged by 1 transistor (power, gnd, 5V signal).

Looks like the miata scheme is completely different and the tach works based on a signal from the igniter. Is that signal on wire 4 a 5V or a 12V signal?
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Old 08-14-2009, 02:53 PM   #6
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So I assume your car uses a distributor, then? Not familiar with the Protege.

The tach output provided by the COPs, if my memory is correct, is an open-collector. In non-geek terms, that means that it provides a momentary closure to ground for every ignition event. To cause something useful to happen with this, we need to add a pullup voltage. In the diagram that DXO posted, a 1k resistor is indicated between the +12 line and the combined tach signal line. So when none of the coils are conducting to ground, that line floats up to 12v. When a coil does conduct to ground, the line goes to 0v.

When the stock ECU is present, it provides this pullup on its IGf wire, which is why that note is there about "MS Only".

In the Miata configuration, we commonly use the tach signals from only two of the coils. Since the normal configuration is wasted spark, we can simply combine the signals from one of the coils on the 1/4 pair and one of the coils on the 2/3 pair, and that will give us one tach pulse for every ignition event. DXO's image shows the blue tach wire going to all four coils, however this is unnecessary.

Your protege, with only one coil, is actually not dissimilar from this insofar as how the tach is going to work. The tach, by definition, must be configured to expect one pulse per ignition event. I assume, since this is in the Megasquirt forum, that you have installed a MS in you car, and that you've already converted to a two-channel wasted spark system. If that is the case, then just take the wire that previously went to your coil(-) terminal and connect it in parallel to the tach terminals of the coils on #1 and #2 (or #3 and #4, whichever is more convenient). This alone may get your tach working. If it does not, than add the 1k resistor between +12 and the tach wire as well.
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Old 08-14-2009, 03:26 PM   #7
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Right now, the car runs on MS2E with toyota COPs in Wasted spark mode with a 4/1 cas (dizzy).

If it's indeed an open collector that goes to 0 at ignition event, I can do like you say and connect a pull-up and using coils 1 and 2, connect the COP tach output directly to my tach. I'll try that tonight.

Just for fun, the protege does use 1 coil and a disty, here are some diagrams:




Joe,
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Old 08-17-2009, 10:30 AM   #8
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Tried without the resistor and with a 1K resistor, still nothing. Just checked in the manual and the coil primary is 1 ohm so I will try smaller resistances tonight, hopefully I don't fry the coils.
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Old 06-14-2011, 05:31 PM   #9
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Resurrecting this thread because my question is related to some degree and I don't feel it warrants a new thread.

While my car is not running MS or cops, my tach is currently inop after my ECU swap. Underdog has the same issue on the same setup and he warned me that I'd have to dig around for a solution. For reference, I do still have the stock ecu installed and igniter connected to the harness, but it's no longer part of the ignition system. I may be able to find a way to use the stock IGf and my DSM igniter tach output if there's no better solution. The Miata and DSM igniters are nearly identical, one exception is the DSMs lack of the IGf pin. I need to look further into how the DSM tach works, but the ignition is also a wasted spark 1/4, 2/3 setup as in the Miata so it's pretty damn similar I'd suspect.

The info above from Joe is very helpful, and I guess what I'm needing to know now is about the actual wire to the tach. Based on the wiring diagram shown below for a stock '92, it looks like the signal wire goes directly from the igniter to the tach (1H, yel-blu), without passing through the ecu. Is this correct? There is also a wire dropping off the tach that appears to be a common power source that runs to the meter fuse (2K, blk-yel), but all my other gauges work so I'd guess that the problem does not lie there.

Also, does the signal from the ecu to IGf do anything other than supply the pullup for the tach signal? If yes, what?
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toyota cops tach output pin-tach-wire.jpg  
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