Tacho peculiarities

[AndyLotus]

That's a great idea.
I was wondering how to check the output without an occiloscope.
I'll give it a try and report back.

Thanks.

[AndyLotus]

Right then, I've double checked earth continuity between earth on the back of the tacho and the earth pin of the ecu. That's all good.

I've checked the output of the ecu and I have a voltage which increases with revs so I guess that means the ecu is outputting correctly.

I disconnected the tacho feed and ran a single wire from the ecu output straight to the back of the tacho.....nothing.

I don't suppose it could be a dodgy tacho could it?

[AndyLotus]

Right, just to follow this up.....
I bought a brand new, cheapie tacho from eBay to experiment with.

I wired it in as per the original and it worked absolutely fine, no need to switch other things on to get a reading. I switched backwards and forwards between the new and the original a few times. The new one worked every time, the old one worked erratically and only when other things were switched on.

I think this proves the tacho is faulty, now to get somewhere to look at it.