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Discussion Starter · #1 ·
12V seems high for a tach singal no? on other cars I've seen it's like ~5v.

I was measuring the voltages on the harness that plug into the ignitor,

and on the wire that is supposed to connect the tach (reffered to as "combination meter" in the factory manual) I was picking up 12V!

Also, doesn't the ignitor send the signal out to the tach? and NOT from the tach to the ignitor?
If so, then shouldn't there be NO power on that wire, when the ignitor is removed???

looking at the diagram there is no indication of voltage or direction of current flow; at least to me, maybe one of you guys can read it better

http://www.mkiv.com/manual/1995_electrical_manual/I/95elec_085.JPG
 

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Hey kmn5... Long time - no see. :)

The NA tach signal is provided by the ignitor based on the collapse of the secondary field of the coil. Consequently, it is a signal that you would not normally encounter. While you might have been reading 12v, the signal is far more complicated than that. My guess is that your "meter" isn't an o-scope. You'll need to input two channels to the o-scope to capture the tach signal - one signal is the tach output itself, and the other is the IGT that triggers the collapse of the coil field (i.e. initiates "spark"). Then, you can "freeze" the tach signal on the o-scope based on an IGT event. I know this from direct experience.

If you pitch the OEM ignitor, you'll most certainly need a tach adapter. MSD makes one that will accept an RPM input signal from either the MSD DIS4 or the AEM. The output of the Tach Adapter is compatible with the NA OEM tachometer.

-scott
 

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Discussion Starter · #4 ·
motorheaddown said:
Hey kmn5... Long time - no see. :)

My guess is that your "meter" isn't an o-scope. You'll need to input two channels to the o-scope to capture the tach signal - one signal is tach output, and the other is the IGT that triggers the collapse of the coil field (i.e. initiates "spark"). Then, you can "freeze" the tach signal on the o-scope based on an IGT event. I know this from direct experience.

If you pitch the OEM ignitor, you'll most certainly need a tach adapter. MSD makes one that will accept an RPM input signal from either the MSD DIS4 or the AEM. The output of the Tach Adapter is compatible with the NA OEM tachometer.

-scott
hey man!
yeah I'm just using a crappy voltmeter, I wouldn't even know what to do with a scope, way beyond what I know :bowdown:

So I shouln't worry about seeing 12v on the tach wire going to the ignitor then?
(thougth this might have been the problem)
I've been trying to troubleshoot an ignition problem that's been killing me, went through 5 ignitors now
see here: http://www.supraforums.com/forum/showthread.php?t=371693
not sure what can be burning them out, I'll prolly just run all new wires to and from the ignitor.
I do have a MSD6btm with the 8910eis tach adapter, but I removed it to make troubleshooting easier
don't supposes the tach adapter can be rigged to replace the ignitor?


the other 2 voltages I got of the ignitor harness was 12V from B+ which is normal (1st pin on the left when looking at the plug head on) and 5V from the pin next to that.
 

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supraswap said:
could you get rpm signal from the ecu rpm wire?
green on the fields harness.
A Fields Harness signal doesn't mean much for the NA ECU. Granted the connectors are compatible, but the signals are different because the TT is direct fire and the NA is distributor.

-scott
 

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kmn5 said:
I've been trying to troubleshoot an ignition problem that's been killing me, went through 5 ignitors now
see here: http://www.supraforums.com/forum/showthread.php?t=371693
not sure what can be burning them out, I'll prolly just run all new wires to and from the ignitor.
I do have a MSD6btm with the 8910eis tach adapter, but I removed it to make troubleshooting easier
don't supposes the tach adapter can be rigged to replace the ignitor?
Sorry to ask the obvious...

Is the ignitor bolted down on its OEM mounting plate? It probably serves two purposes: 1) chassis ground and 2) helps cool it.

Also, the tach adapter can't be used to replace the ignitor.

-scott
 

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Discussion Starter · #7 ·
supraswap said:
could you get rpm signal from the ecu rpm wire?
green on the fields harness.
yeap, I get the rpm signal just fine
my wideband and afc2 's rpm matches the one I get from the tach
 

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Discussion Starter · #8 · (Edited)
motorheaddown said:
Sorry to ask the obvious...

Is the ignitor bolted down on its OEM mounting plate? It probably serves two purposes: 1) chassis ground and 2) helps cool it.

Also, the tach adapter can't be used to replace the ignitor.

-scott
no prob, it's a valid question, :)
and yes it's bolted down well with good contact,
I even sanded the undside contact points and put a dab of white lithium grease on it

based on everything I've check so far there must be a short in the harness somewhere, but what's puzzling is that the short is not immediate, it takes the ignitor like 2-3 weeks before it dies

my other option is to go all out and get the AME ems and covert my ignition system to coil packs using the 7m-gte CPS and 97+ NA coilpacks and ignitor

I've changed the distributor and the coil, there's no other major component involved, been looking over the factory wiring diagrams.

I've already picked up 500 feet of colored copper wires for the wire transplant
just have to wait till the weekend before I can start

don't suppose the noise filter is bad? :dunno: that would just kill me, a .25 cent part causing all this damage
http://mkiv.com/manual/1995_electrical_manual/I/95elec_065.JPG
 

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Didn't read through all the posts.

I'm pretty sure it's 0-5v. That's how it was adjusted back when I had the Innovate LMA2 wideband kit. The LMA2 could only read voltages that are 0-5v.
 

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Discussion Starter · #10 ·
michaelvanle said:
Didn't read through all the posts.

I'm pretty sure it's 0-5v. That's how it was adjusted back when I had the Innovate LMA2 wideband kit. The LMA2 could only read voltages that are 0-5v.

Hey Mike, what's up
ummm, think your talking about the other end, where the tach wire connects to the ecu, yeah that side should defintely be 5v.
I'm looking at the other side now, where the tach signal originates from the ignitor-> gauge cluster -> ecu
 
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