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The T2 ecu in my Porsche 914 flatly refuses to talk to the tacho. The original Porsche tach (usually) requires an adaptor, being an older design, and tried both Emerald and Ghetto Motorsport adaptors, but to no avail. Thinking the tach may have been damaged internally (it worked off the original coil/distributor OK but has never worked since changing to the ecu/crank trigger set-up), I acquired a new Racetech tacho. On switching on, the needle sweeps across the scale, showing the tach is a) receiving power, b) is earthed and c) well, working. Go to start the engine and the needle doesn't move.

I have checked for continuity between the ecu and the tach along the existing loom, which is all OK. To make sure, I ran a new wire directly from the ecu to the tach, but to no avail. I am using PWM4 (Pin 26) on the T2, as recommended by DTA. The ecu has already been back to DTA and given a clean bill of health by Alex.

I am at a loss.

So what sort of signal should it be receiving ?

You say it needs an adapter....what sort of adapter ? You say you've tried different adaptors....has anyone said these would work with your specific tacho ?

Exactly what originally triggered the tacho ? how is it normally wired ?

It's well known that early Porsche tachos need a helping hand, via an Emerald, Ghetto Motorsport, Bob Ashlock etc adaptor to boost the signal. In the past, when running a Porsche 911 with Jenveys and Megasquirt, an adaptor from Bob Ashlock solved the problem. Yes, these adaptors work with 1970s Porsche tachos, which were originally triggered by the coil.

The replacement tacho is a brand new unit from Racetech, which can be wired to run from an ecu, such as the DTA units. You have the option to wire it direct to the ecu, or to a conventional 'points and coil' set-up. Others have them working together OK (they're popular with the hillclimbing fraternity).

Having checked all wiring for continuity, 12v feed, earths etc, the finger is pointing towards the ecu and Alex has kindly offered to replace this for me.