Garmin G3X / s6ln-204 mag / UMA T1A9-2 sensor -SOLVED

[rv8bldr]

Hey folks

Pretty specific title, i know. Here's the problem:

I have an O540-A1D5 with Bendix SL6N-204 mags. I also have a Garmin G3X system using the GEA24 engine interface system. One of the default sensors you can use with this setup is the UMA T1A9 Hall effect rpm sensor. It screws into the vent hole on the mag.

During my first engine run (and subsequent runs) it is showing an rpm of 0. I triple checked that the sensor is wired as per the Garmin install manual and the sensor drawing. Nada.

So i thought that in the years since i bought it i must have damaged it somehow so i bought a new one.

Same deal: 0 rpm.

The configuration of the rpm channel in the G3X is correct (checked multiple times), and the writing is correct.


Anyone out there have the same problem at some point, and if so, did you figure it out? I'm hoping it isn't an internal with the GEA24 as the warranty is long expired even though last Thursday was the first time the engine was run.

Thanks in advance

[Untainted123]

Hey Mark! I looked at your Maule at Oshkosh when I was between planes, but I ended up with a Bearhawk 4A of my own Glad to see you’re getting close.

Can you specify exactly which pins on the GEA harness you have it hooked to?

In my G3x install manual, Table 24-1, on page 24-5, it specifies UMA T1A9-1 for Slicks and T1A9-2 for Bendix. Can you verify you have the correct sub part number, is it marked clearly on the sensor? I think they might be 2 different size threads, so maybe it’s not possible to switch them up….

Do you have the sensor in the correct vent hole? The correct hole is the one where you can see the magnets, not the gears. Also, the sensor must be fully seated to be close enough to the magnet I believe.

[rv8bldr]

Good day! I do remember meeting you at OSH, although i have to apologize for completely forgetting your name (as i do with most people about 45 seconds later :-)

Thanks for the reply. I do have the correct sensor; the Slick sensor won't fit in the Bendix mag. There is only one hole that i can see in my mags and it *looks* like magnets in there. I certainly don't see gears. The sensor is fully seated as per the UMA documentation (finger tight, then 1/6 turn tighter).

I'm using pins 7,8, and 9. IIRC, blue/white (ground) is on 7, white (signal) is 8, and orange/white (12 VDC) is on 9. Being old, i may recalled that wrong, but whatever they are supposed to be, i verified it by looking at the wires going into the sockets with the G3X doc in hand.

My buddy and i are going to put a scope on the signal line tomorrow to see if I'm getting anything. I'm also considering moving the connection to RPM2 on the GEA connector on the off chance that the RPM1 circuitry is dead. Not sure how the PFD would handle that, though....

[Untainted123]

Mark, I have the same problem with names.

That appears to be the right wiring. Did you also configure the sensor type in the GEA/G3x config menus (Chapter 30.4.32.2 Engine/Airframe Input Configuration and page 30-187 of the manual)? If for some reason you have to use RPM2, I don't think the unit will care, you can configure it to show either/both if I remember correctly, and call it simply RPM. I would verify also that pin 9 is actually putting out 12vdc also, and that pin 7 actually goes to ground. If not, you could pick up either of those from any other pin that does. I have also seen it (multiple times) where the socket was not fully seated/clicked into the harness, and when plugging it in, the socket is pushed back and out of the harness by the pin coming in. And all the normal harness making caveats apply (ask me how I know): did you put it into the right hole, count the right number of places over etc

Just for reference: image.png

Note 6: THE RPM CHANNEL CAN BE CONFIGURED FOR UMA TACH SENDERS SHOWN OR 4 OR 6 CYLINDER ELECTRONIC IGNITION INPUTS.

[rv8bldr]

Welp, that's embarrassing. I looked over (what I thought was) every square inch of those mags and didn't see another port...until today. It is REALLY hard to see, but it is on the inboard side (towards the center of the engine) very close to the accessory case. It was an absolute bear to get in there. My engine has the oil pressure and temperature housing on the back of the accessory case so I had to remove that. There is a B&C backup alternator installed there too. However, I finally managed to get my gorilla hands in there to remove the plug and install the sensor.

After reinstalling everything I had removed I ran the engine and lo and behold....the tach works :-) I borrowed our EAA chapter handheld RPM sensor and the RPM on the G3X was bang on the hand held sensor.

So, for future people using this combination of G3X, UMA T1A9-2, and Bendix mags, the port you want is on the inboard face of the mag near the accessory case. Install this BEFORE you mount the engine. It will save you a lot of grief !

BTW: I shut down the engine thinking I had fixed the last issue before my final inspection only to find some oil drips from the CS prop/crank seal area. I ended up pulling the prop and it looks like the O ring on the inside of the prop hub had failed in some manner. Not surprising since I had it overhauled 7 years ago and it has been sitting in a guest bedroom ever since. I think it dried out. Now I need to order and wait for a new O-ring. No inspection for a while yet...Sigh

Cheers

[jaredyates]

I try to keep an extra for each gasket and o-ring on hand but am always finding new ones that I failed to stock. You might consider replacing the crankshaft seal too, if it has also been sitting for a few years. 90% of that job is removing the prop, and you're already there.

[Untainted123]

I borrowed our EAA chapter handheld RPM sensor and the RPM on the G3X was bang on the hand held sensor.

Glad you got it sorted out. I have had success with this app (iPhone) on our noisy airplane engines, if for some reason you didn't have access to a real one:
image.png

[Untainted123]

I ended up pulling the prop and it looks like the O ring on the inside of the prop hub had failed in some manner. Not surprising since I had it overhauled 7 years ago and it has been sitting in a guest bedroom ever since. I think it dried out.

I believe this can also happen if you aren't completely aligned when installing the prop, and make sure you keep it aligned as the bolts bring the prop onto the flange, working your way continuously around (which you kind of have to do anyway because of the clearance). I also oiled the o-ring before putting the prop on for that reason, to make sure it didn't get rolled.

[rv8bldr]

I believe this can also happen if you aren't completely aligned when installing the prop, and make sure you keep it aligned as the bolts bring the prop onto the flange, working your way continuously around (which you kind of have to do anyway because of the clearance). I also oiled the o-ring before putting the prop on for that reason, to make sure it didn't get rolled.

Ya, I have always been a little afraid of that happening. I don't know if that caused my issue or was just age related.

Note for everyone with a Hartzell CS prop:

You may already have one of these, but this wrench from Anti Splat Aero is awesome. It makes tightening and loosening the nuts on a Hartzell sooooo much easier. I showed it to the owner of my prop shop and he immediately ordered two. I am not in anyway affiliated with them, just a happy customer who has installed and removed his prop a number of times over the last few months...

https://antisplataero.com/product/ultimate-propeller-wrench/

https://www.youtube.com/watch?v=vFUg...BzcGxhdCBhZXJv (not a professionally produced video but informative and only 6:31 long)