tach issue
 

My 930 tacho dies between gear shifts , ie drops from say 5000 rpm to dead between shifts. It then comes alive again a few seconds later and hits what looks like correct revs. Then dies again at next shift.
I have checked alternator out put - 13.4 V at 2000 rpm.
Is my tacho on the way out, or is it a symptom of something else?
Thanks
Alan

Is the output steady of the alternator? Within a few hundredths of a volt? 13.8+ volts is more of what I see with working V-regs.

Yes, seems stable - was not bouncing around. Seemed about the same at 1000 rpm too.
The other thing I should mention is the tach is quite happy idling at 1000 rpm and up to 2000 and back to 1000. It seems to die in the big drops in rpm. I wonder if some internal damping thing has failed and it just drops to the floor til it picks up a voltage again, or something.
Alan

I'd be inclined to say that your tach might be showing signs of failing, but I'd definitely be concerned about a voltage regulator starting to fail. Usually, a tach starting to "flip out" is a sure sign that a VR is starting to take a dump. I'd break out the voltmeter and start taking some readings to rule out the VR first.

How would you rule out the VR? I thought a stable 13.4 would be OK. I guess I could see if it is spiking at 5000, but not too keen on that. Could try revving it a bit higher - but the tach is reading OK at those revs, it is when I drop the revs that the problem occurs - but it is holding 13.4V at the lower rev end. I wonder if it is just falling free- fall and something in the mechanism is supposed to dampen that.
Alan

I would ask Racing Ray if he has a spare you could swap in for a quick fault elimination exercise. I think he has a bunch of guages left over from the leopard car. (RIP, that was the most exciting ride I ever had around Puke)

What happened to the Leopard? Did I miss something?
Alan

I thought he broke it some years ago?, the Ivory Beast is still driving I believe.

as usual, I neglected to read the entire post....I just saw that you've already done a diagnosis. I'd probably rule out your VR. I apologize for my uninformed post (again).

I had a think about this problem and I do not think the tacho would be the likely cause. Its a simple pulse driven amp voltage output to a standard damped meter. Maybe try attaching one of those cheapo tacho/dwell meters you can buy at Jaycar and see what happens. I would be thinking about what could possibly disrupt the pulses from the distributor to the tach during shifts, presumably the motor is running strong. Is there a over rev or shift light wired in or some exotic electronic thingy on the wastegate?