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Posted: Wed Jan 11, 2012 6:25 am
by brentp
This would be no different than a properly made home-made diode circuit.

Could you describe your problems? Does it always read low RPMs? If not, does it read exactly 1/2 RPMs when it's exhibiting the problem?

Posted: Wed Jan 11, 2012 4:33 pm
by 73tii
hello Brent,

Tach was efficient for a few weeks but the problem became more consistent over time. but yes..reading is consistently low now.

below is how I did my circuit.

Posted: Thu Jan 12, 2012 9:46 pm
by 73tii
is it possible the diode is shot? anyone?

Posted: Thu Jan 12, 2012 9:53 pm
by brentp
We're not familiar with that circuit design- it's different than what we have, but it seems that it could work. You might want to check connections on the diodes - if all connections are good it's possible one of the diodes might need replacing. Replace both just to be sure.

Make sure you're using diodes rated for at least 400V - like a 1N4004 or equivalent.

Posted: Sun Jan 15, 2012 1:49 am
by 73tii
found a short in the wiring which subsequently affected the tach to be lazy. All is well now. Thanks Brent.


Posted: Sat Sep 22, 2012 8:17 am
by essexstu
Good morning, before attacking my wiring loom, wanted to check where to place the circuitboard i just recieved. Im running a v6 with wasted spark and an after market ecu - Vi-PEC (the same as link). My tacho is a standard Ford one and expecting the 400v, but the aftermarket ecu only puts out 12v.

Understanding the circuit board needs the 3 pulses, but does it need the 3 pulses from the ecu (low voltage) or the 3 pulses after the ignition amplifier that go direct to the coils?

Many thanks

Posted: Sat Sep 22, 2012 3:39 pm
by brentp

The board is designed to tap off of the drive lines for the coil packs - after the ignition amplifier you have.

Posted: Sat Sep 22, 2012 7:57 pm
by essexstu
Worked a treat thanks :-)

Posted: Sat Sep 22, 2012 8:38 pm
by brentp
That's great to hear! Thanks for the feedback.