Joined: 30 Sep 2010
Location: The Netherlands
When you swap a DOHC 4g63 into the Starion and wire up all the electrics you will notice that the tacho doesn't work..
You can fix that using the '90 eclipse module.
But you can also just mod the tacho itself so it accepts the tacho signal from the ecu.
I am using this mod myself using a evo 8 ecu providing the tacho signal.
Since pictures make things alot easier :
Starion tacho when taken from the cluster:
The electronics of the tacho: Notice the resistor in the middle (Red,grey,orange,gold) this is the input signal resistor buffer so the electronics don't see the full volage from the coil.
New resistor + diode in place (will explain later)
And another (pull up)resistor in place that will be hooked up to the input voltage
Added some shrink wrap to tidy it up
So now some explanation:
Basically what this mod does is invert the input signal.
The normal input signal is a positive voltage on signal pulse.
The evo 8 however is a negative ground type signal, so it grounds the signal on pulse.
So the mod inverts that signal to make it work.
By supplying a constant voltage to the input of the tach that is pulled down by the ecu.
I got the idea by examining a Eclipse Tacho and basically copied the input circuit from that tach.
original : 28K Ohm
input side resistor : 12K
pull up resistor: 6.8-6.9 K
and used a simple diode as a input protection in the same way a eclipse tacho has.
It's not advisable at all to tap into the cam signal, just use the ignition module.
I just used the example from Megasquirt and it works flawlessly with mitsu tachometers.
All you do is use a relay to create the high voltage spike that the tach is expecting to see.
You can then feed the pulses to the circuit directly from the ignition module (where it says Megasquirt in the diagram) with a little help from some 1 way diodes like such:
Or you can use the example directly above and wire the diodes directly to the coil negatives and get the same result as the factory module.
Im using the upper example and it uses the factory ECU tachometer signal...
I just think you have a slight misunderstanding of the way these tachometers really work is all... because I also found that if you ground the TE lead and feed the ECU signal directly to the Ground lead (which sounds stupid I know) it also seemingly triggered the tach... until you took your foot off the clutch, then it simply wasnt seeing the required spikes in voltage above 12v that it needs to properly trigger the tachometer.
and judging by your pictures posted above and this Mighty Max tachometer I have torn apart right in front of me, Mitsubishi seemingly uses the identical part in every tachometer and simply adapts the face plate and needle to the car its going into.
I'm using DSMlink and a 91-94 wiring and components, and my tachometer did not work off the ECU tachometer output wired directly to the starion tachometer.
I too had to use the 90 tacho interface to get my tachometer to work (used the noise filter but it didn't make a difference), but although it was working it wasn't correct. I don't know if anyone else has compared the tachometer to whatever your engine management is saying your RPMs are, but when I checked the tachometer was slightly slower than it should be and at times up to 500rpms off what DSMlink was showing me. Without looking at link at the same time, I would have never guessed it was off because it looks really good. I set my rev limit to 5k rpms just to check and I was hitting the rev limit of 5k rpms, but the tachometer was showing me at 4500 rpms.
Using the method that Richard mentioned first in this thread made my tachometer read correctly. Thanks Richard.
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