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I have a 90 colt w/ 4g63 swap. I am using a 90 harness that I converter over to 91+. My question is, the noise filter on the 90 harness thats converter to a 91 now, do I leave it alone & get another noise filter to wire in to make the tach work? Or Can i cut that noise filter out & wire it between the wires by ecu to make the tach work? It seems like the tach wants to work when I reeve the engine but it doesnt show any idle at all..

thanks.. .

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Speed kills!! Drive a Honda & live forever!

I wish my tach would work. Ive got all 90 harness and sensors with a 91 ecu, and the noise filter is wired directly to the cluster into the plug by the ecu. It only works sometimes and is very inconsistent, I believe its a voltage issue or something, anyway I hope you dont have the same problem.

yea i using 91 ecu, the harness is converted to a 91. do i leave the noise filter on the harness and wire a additional one in? or can i cut the noise filter off the harness once its converted to a 91 and wire it onto tach wire?

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Speed kills!! Drive a Honda & live forever!

Run the tach via the filter, from a 90 DSM or 1.6L CSM "tacho interface" that's mounted on the coil.

Run the ECU on a seprate wire with no filter from a 91 power transistor tach output pin.

You will be using tach signals from two seperate components.

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"A good day racing is better than a great day fishing!"

I have used this guide: http://www.dsmtuners.com/forums/article ... iring.html to use a few '91 ECUs in '90 cars.

So I leave the noise filter on the 90 harness that i converted to a 91? and then from ecu wire no noise filter? to the 91 transistor tach output pin? what color is that power transistor tach wire? are you talking about the tach wire? sorry the questions.. just kinda confussing converting the 90 harness to a 91 to work with 91 ecu.

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Speed kills!! Drive a Honda & live forever!

The link I gave has pictures showing wires and such. If the colors arent exactly correct you can always consult an FSM found here: lilevo.com/mirage

Usually the tach wire would be the white one.

Only the tach signal needs to be filtered, and you should be getting that signal from the white wire on your square 4 pin coil plug. If you have the triangular 3 pin coil plug, then you have the wrong coil.


The RPM signal to the ECU should be fed filterless from the 8 pin (2g MAF style) plug at the 91+ power transistor. Should also be a white wire (pin #4 or #5 IIRC).

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"A good day racing is better than a great day fishing!"