Likely culprits for zero tach readings?

[NM Doug]

[EDIT: we think we found the problem part and are now looking for a replacement - see post #2]

We thought we had this sorted after an earlier occurrence - we had found a couple loose nuts on ring terminals and spent some hours cleaning up the wiring harness, but...

We have two tach sensors - one on the mag which goes via an RDAC on the engine side to our MGL EFIS, and one mount-on-the-engine type that goes to a round gauge.

After landing today (not a hard landing, either...), we taxied off the runway, and both tachs dropped to exactly zero and stayed there, though the engine kept on running normally. Other than a running engine, what things might be common to both sensors? All I can think of is a power bus connect point or a ground bus connect point.

[NM Doug]

We were wrong about there being two senders - there's just the one, and it appears to be the problem.

We have an older O-320 (no suffix). The sticker on the back of the sender reads 59D-05059 0801.

Is this a stock Van's sender, and does it come with the wiring? If not, does anyone have a part number and source for this offhand?



Another view - this is an older pic, when we still had the oil screen:

[Canadian_JOY]

I've had this same sender fail. Do yourself a favor and buy a short tach cable from Spruce (12-18", whatever works) and mount the tach sender on something other than the engine. Mine is mounted to the firewall using a simple Adel clamp setup.

Heat and vibration seem to kill these senders. Get it off the engine and it lives a much happier life.

[NM Doug]

Thanks - that sounds like a great idea. Is this a Van's standard sender, though? This Spruce one?

Also, if you recall, did the replacement sender you bought come with a long cable or just a short pigtail?

Originally Posted by Canadian_JOY

I've had this same sender fail. Do yourself a favor and buy a short tach cable from Spruce (12-18", whatever works) and mount the tach sender on something other than the engine. Mine is mounted to the firewall using a simple Adel clamp setup.

Heat and vibration seem to kill these senders. Get it off the engine and it lives a much happier life.

[Canadian_JOY]

The Vans gauges are made by ISS, so that sender you referenced from Spruce will do the trick. As for the leads on the device, you might get a foot or so of wire. Most installers put a connector of some sort on there to allow the sender to be replaced. If that's the case in your aircraft, you'll need to take whatever connector is on the end of the wire for the old sender and get that connector installed on the end of the new sender wiring. Wires are color-coded to help avoid confusion.

[NM Doug]

Good to know about the source - thanks. Our install doesn't have any connectors (yet) - so we'll retrofit one, I think.

Originally Posted by Canadian_JOY

The Vans gauges are made by ISS, so that sender you referenced from Spruce will do the trick. As for the leads on the device, you might get a foot or so of wire. Most installers put a connector of some sort on there to allow the sender to be replaced. If that's the case in your aircraft, you'll need to take whatever connector is on the end of the wire for the old sender and get that connector installed on the end of the new sender wiring. Wires are color-coded to help avoid confusion.