Electric Tach reading wrong

[jeff beckley]

I have the vans electric tach installed on my 0-360. It started to read 1000 rpm low. At full power the tach reads 1200 rpm and 0 rpm at anything less than 50% power. Not sure where to look.

[N941WR]

Jeff,

We need some details to help you out.

What type of tach do you have? (EMS or traditional tach and make and model?)
How is the tach signal picked up?
Do you have electronic ignition or mags?

[groucho]

I'm not sure if this even applies, but...

I have an Advanced Flight Systems engine monitor with an RPM sensor that screws into the mag. One of my spark plug wires worked its way loose (on my electronic ignition, not the mag), and the RPM readings were all wrong. I fixed the electronic ignition's plug wire & the RPM readings returned back to normal.

[jeff beckley]

I can not find the model number but it is the kind that attaches to the conventional accessory case in place of the cable style. It is a round generator that has three wires going out up to the tack in the panel. One of the three wires is connected to power.

[andyrv]

Is there a way to set the tach gauge for pulses per rotation? I am using Van's tach sender for an EFIS and the sender I received puts out 8 pulses per rotation of the engine which had to be entered into the EFIS to get the correct RPM reading.

Andy

[Mike S]

Originally Posted by jeff beckley

It started to read 1000 rpm low.

So, it used to work correctly, and now is acting up?? How many hours on the plane before this problem started??

I would suspect the sender, just because that is where there are moving parts.

This of course assumes you have checked all the electrical connections.