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Location:
Sydney
Registered:
August 2002
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ae86 microtech!!!
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Thu, 15 August 2002 09:24
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anyone know the trick to getting the standard tacho working in a sprinter when running microtech???
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I supported Toymods
Location:
Northern Beaches
Registered:
May 2002
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Re: ae86 microtech!!!
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Thu, 15 August 2002 10:27
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doesn't it just run off the negative of the coil?
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Location:
Sydney
Registered:
August 2002
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Re: ae86 microtech!!!
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Thu, 15 August 2002 10:29
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i tried that but i think the mt signal is too weak!
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Location:
North Sydney
Registered:
May 2002
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Re: ae86 microtech!!!
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Thu, 15 August 2002 12:58
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Are you running multi-coil packs?If yes you need a signal multiplier.
As ribbo says, doesn't it run off negative side of coil? If the signal is too week there your car wont even run.
Or else just use the tacho output off the microtech. Put a cro or spare tach on it to make sure the sig is working, they blow easily.
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Registered:
July 2002
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Re: ae86 microtech!!!
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Fri, 16 August 2002 13:56
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yeah have the same problems, multi-coil pack..
negative side of the coil will drive the original & aftermarket tacho, but will only display half the revs.. (ie. 2000rpm when it's 4000rpm as displayed on the handset)
and the tacho output of the microtech mtx8 won't drive any tacho, I've checked with voltmeter, the voltage is slightly lower ( < 1v ) than the voltage on the negative side of coil, but don't understand why it can't drive any tacho..
what's the signal multiplier? Where to buy? Or are you talking about the ones that you built with ICs on circuit board?? Anyone with same experience?
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Location:
North Sydney
Registered:
May 2002
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Re: ae86 microtech!!!
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Sat, 17 August 2002 01:25
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Just hook the mtx tach output to the dash, if it doesn't work there is something wrong with mt or your dash. Voltmeter wont measure it, so fast 1000times a second at idle and should have a flyback of about 300v which your dash triggers off.
send your mt in to get fixed. dont cost much
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Registered:
July 2002
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Re: ae86 microtech!!!
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Sat, 17 August 2002 08:37
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but last time I measured the voltage, it's starts off around 12v (11 point something) and drops as the revs goes up, seems fairly normal, any other ideas?
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Location:
North Sydney
Registered:
May 2002
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Re: ae86 microtech!!!
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Sat, 17 August 2002 08:58
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it drops because as the revs go up the coil is switched off more often(less charge time) because it has to fire obviously more often.
You cant measure it with a voltmeter. It happens too quickly and a voltmeter only gives you an RMS(false type) approximation. Your measuring the voltage with a DC voltmeter but the signal is switching on and off so quickly its almost AC signal.
The tacho triggers off the back EMF(or flyback) which you cant see it happen on a voltmeter. Voltmeters are good to see if power is on the coil, thats all.
If you have a microtech they deliberately give you a tacho signal thats fires for every crankshaft revolution. Perfect for your tacho. Even better for if you run multi-coil packs because the signal wont trigger enough times for the dash to read correctly.
If you dont have a microtech and are running multi-coils you need a multiplier.
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Registered:
July 2002
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Re: ae86 microtech!!!
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Sat, 17 August 2002 14:31
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that means the voltage drop across the tacho output of the microtech and the battery positive should give a reading on a meter right? I'm going to test it tomorrow to see if the voltage drop is 1) Linear, and 2) Consistant, as if it is consistant, then I can use the voltage drop to control a circuit which I can use to turn off the VVT solenoid at 7200rpm right? Then if it's Linear AND Consistant, that mean I can use the signal to drive a Linear analog meter right? If only it's that easy! 
anyway, so Paul, how does the multiplier work? As the signal from the Microtech isn't able to drive the tacho at all, and currently I have the OEM Tacho connected to the negative side of the coil and it's only showing half the revs! 
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Location:
North Sydney
Registered:
May 2002
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Re: ae86 microtech!!!
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Sun, 18 August 2002 10:58
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GT20V-Im completly lost as to how your trying to turn off a solenoid at 7200rpm. I know what you want to do though. The voltage wont be linear and consistent. Your meter wont work!!!! They are crap, ordinary volt meters.
There is 12 volts on the coil right. Magnetic field(flux) goes to the secondary and then when the 12volts is turned off either by the points in old type distributers or an igniter(simple amplifier) in newer cars the 12 volts drops. When this drops the flux collapses and a very high voltage spike is sent to the sparkplug.
At low rpm there is enough time for the 12volts to stay on longer and give a better spark but as the engine speed increases the 12 volts has less time to stay on therefore it is off more often.
Now to make things worse, from your point of view.Because this will most likely stuff up your circuit. When the flux in the secondary collapses and the high voltage spike goes out to the sparkplug it is also then re-induced back into the primary side of the coil. Which is the 12 volts side.
So with an oscilliscope and only an oscilliscope you will see 12 volts there, then it will switch off. A few nanoseconds after the 12volts drops a massive( i mean huge) spike is seen. This is approximately 300 volts in amplitude. Its called back EMF(ey Ed).
This might stuff up your circuit, be carefull.
Now the tacho uses the spike to "trigger" off and turns the needle around further. More spikes more turn, not more "coil off time" more needle. If only it were that easy.
The multiplier just doubles that signal using a frequency timed circuit.(for a 4 cylinder using 2 coil packs(waste spark type))
Or like on my car with 3 coils for a 6cylinder it triples it. I'm sure it could be done with some power diodes(cost like $4)
Anyone done it instead of buying a damn expensive multiplier???
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Registered:
July 2002
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Re: ae86 microtech!!!
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Mon, 19 August 2002 15:18
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Hi Paul, I won't care if the 300v fry the circuit coz it's a cheap one, and will be controlled by a relay therefore isolating the VVT solenoid, I haven't went to check the voltage yet, but if there are 300v, I'm sure these can be filtered out, but I'll test my idea later..
but I still don't understand the multiplier and the diode circuit that you're talking about, any circuit diagrams?
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Location:
Syndey
Registered:
December 2002
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Re: ae86 microtech!!!
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Mon, 14 April 2003 01:03
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Use you AUX output to switch at 7200rpm,
Dale
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