SonexBuilders.net

Hi all,

I have a Princeton probe in my Sonex that has worked flawlessly since 2008. Lately the fuel levels will drop to zero then climb back up. The levels might drop 3 or 4 times a minute, very erratic. When the levels go back up they might go to the proper level or they will show any level, except more than is actually in the tank.

I have e-mailed Princeton, they mentioned loose wires which I already checked. Wondered if anyone else has had this issue.

I used 100LL with the Aerovee and use 91 with the CAMit. The CAMit engine ran for 90 hours before the level started fluctuating. I have never used Ethanol fuel.

The probe is being read from an MGL Enigma EFIS.

Thanks for any input,

Ken Woodraska
Sonex 959
CAMit 3300 106 hours

Make sure the ground wire is attached to the probe and grounding point. When I first installed the probe I forgot to attach the ground but the sender worked for awhile. When it quit working I found the ground completely missing. The way it was working prior was the throttle cable (metal casing) was resting against the brass probe and provided a path to ground. The cable housing was moved and the probe no longer had a reading. After attaching a ground wire to the brass fitting it resumed operation. I calibrated the gauge for use with auto fuel, when forced to use 100LL the reading is off. This is also on an MGL Enigma.

Hi Ken
Its hopefully just a bad or loose connection. Just turn the instrument on. If its showing a stable reading poke around and wiggle the wiring to see if you can make it happen.
Mine had also performed flawlessly till one day I noticed the fuel level decreasing real quick in flight. Turned out it was only the grounding lug on the brass sender fitting had come loose. I didnt notice the level increase to more than I had in the tank at the time, but it was fluctuating.
Steve
Sonex 892

Had similar problem. Seemed to be the connection between control unit and sensor, but later found it was vibration of the control unit itself. Was mounted to fuselage side wall, re-positioned it to mount between the two angles running up each side of spar box. No more problems.

David A. Sonex TD, CAMit 3300.

Bill, Steve and David,

Thanks for he replies. It does seem like a connection problem. I wiggled all of the connections and connected the ground to a different post on the buss after work the other night, the reading never wavered.
I have not had a chance to test in flight. I will check the control box for looseness and if the readings are still erratic I will replace and reconnect all the wiring ends.

Hope that works, I really don't want to mess with anything on the fuel tank for fear of starting a leak. Might have to go the backup camera route if I can't figure out the problem.

Thanks again,

Ken W
Sonex 959
CAMit 3300

I had the erratic readings also, and found it was the black plug in connector between the fuel probe and the unit itself. With the connector still plugged together, it would have the erratic readings if I didn't hold the plug together with pressure by hand. I used zip ties to hold it together with pressure. I'll see if that works.

Does anyone have easy access to the bottom of the Princeton fuel probe? The eyelet for the ground wire on mine is loose and it is impossible to see. Is the eyelet is attached to the probe with a screw or how is it attached. Slight movement of the eyelet makes the EIS read correctly so I suspect the eyelet connect to the probe body is not making good contact. If it a screw attaching the eyelet to the brass body I can try to tighten it up or if all fails I will attache a ground directly to the brass body with a clamp. Replacing the probe is a task requiring de-fueling and then recalibrating the probe so I would like to avoid that task.

This it?






Wes

Thanks Wes! I thought I remember it being a screw there but I could not get a good angle with a mirror to confirm it. Now to see if I can get lucky and get a screw driver on it.

My probe has a short common screw holding the ground eyelet in place. Looks like it back out due to vibration or etc. Suspect it may do it again so I am going to get a non cushioned adel clamp to fit the brass probe body and try to rig a more secure ground point.