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Engine Specific Info and Questions => IDI Engine => Topic started by: tdan on March 29, 2013, 05:14:41 pm
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Here is some information on how i got the tachometer and
oil light/buzzer working on my Mk3 2.0 that i converted to a TD aaz.
My two main sources of information were 2 following websites.
http://www.4crawler.com/Diesel/CheapTricks/Tachometer/index.shtml
http://www.a2resource.com/electrical/management/motronicvr6aba.html
From what i could gather the computer sends square 50% duty or a shorter pulse?
could not figure out exactly, not having a running 2.0 motor car.
But from a signal generator plugged in to pin 22 on the ecu plug,
the tach would start working at +6 volts of signal and did so all the way up to +13.
And it would need to send 2 pulses for every crank revolution. 4 pulses
for every camshaft or injection pump revolution.
So any way you could get 2 square pulses peer crank rev of +6-7 volts or more,
the tach will accept and not care for amplitude or pulsewidth? , just the frequency.
The only thing sitting inside timing cavity is the reflective wheel which happened to be
a silver computer CD which had reflectance for my sensors just below
aluminum foil which i first considered but still very good. But the CD offered a plastic
stock that was already very close to size i needed.
The inside of a cd gets drilled out with a 2 1/8 inch hole saw bit. and
the outside get a 1/8 of an inch ground of all around to fit down to the flats
of the camshaft pulley (On my aaz diesel injection pump pulley cannot
work as it has 3 timing screws in a split pulley). Then with some masking tape
i made 4 open and closed areas , open areas get sanded with a Brillo pad to
rough it up for better paint adhesion. and the whole thing gets sprayed
flat black color. Also the back of a cd gets roughed up also to get a
better gluing area , which after everything is done gets siliconed to the
crank pulley. Make sure the cd sits on the flats of the pulley and doesn't flex much.
And be gentle with cds as it is plastic that shatters easily, i broke a few
before getting it right.
I had radioshack infrared diode and an infrared photodiode.
But those require some amplification and buffering for the tach, doable with
an extra transistor.
The perfect part ended up being nte3036 and nte3032 . i ended up using
3036 before i realised 3032 had a way shorter rise time but the 3036 was
still fast enough for the tach . at higher rpm on a scope the rising
pulse of the signal on 3036 was not as square as 3032. Both
of those phototransistors worked off a fiew dollar white diode,
or a bit less sensitivity off a yellow cheap diode.
Base leg on the phottransistor did not get used as i could not see it
doing anything, maybe it was an old part and i did not test others,
but biasing it from 12 v to 0 trough 1meg resistor changed nothing on the
output during dark or light.
So the whole sensor ended up being 3 wires: positive , negative, and sensor output.
The diode gets a 600 ohm resistor as to limit current from 12-15v
Phototransistor gets a 10kohm from positive to collector , thats where we
tap the signal wire from , and emitter gets grounded.
Sensor sits inside male pvc threaded cap that has 2 holes drilled for diode and transistor.
slightly angle towards each other to get a good bounce of light
from half an inch to an inch , which is how far it will sit from the reflective surface.
And the threads get cutoff halfway to make tightening the female cap over it easier
which holds the whole sensor on the timing cover.
Sensor ends up sitting in a timing belt cover over the middle of the cd area.
After drilling the hole in the timing cover , put the cover on and test how far
away it sits from the already glued on cd and to make sure its not too close
to center or edge of the pulley as not to cause interference with the sensor.
Sensor gets plugged in to ecu plug that's is disconnected from the ecu
0 -ground
22 -signal
23 -power that is on when the key is on , verify by led being on.
Dan
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Very nice work I assume it is obd2