Johnnybgoode Posted February 26, 2015 Report Posted February 26, 2015 So I'm overseas for a bit and have some time to think about troubleshooting my fuel quantity system. I have a problem with each tank, but the JPI and my habit patterns keep me honest on always having enough fuel onboard. Still I don't like squawks and need gauges by annual time. I've been thinking about the issues and would like some other minds to weigh in. Known things to fix when I return are the grounds - both are now run about 6 inches from the sending unit and grounded to the airframe there. I can tell the crimps and terminals are aftermarket from the aviation dept at Advance Auto. Connections are clean but I think I'd have fewer suspicions if I ran them both back to a ground plane nearer the gauge cluster. Now for the problems... My left gauge is intermittent inflight but mostly shows empty on the ground. To me that smells of a bad connection on the power side of the system or a failing sending unit. The fact that the sending unit works inflight leads me to believe that it's not totally out to lunch. Plan to start troubleshooting by checking continuity of that power wire on my return home. Right gauge is always off-scale high, which I have read is a ground problem. Could it be as simple as that ground wire needing run to the same ground terminal as the gauge cluster? I know that the whole plane should have the same ground, in theory, but I have just "fixed" two "hot" cylinders on the JPI by rewiring the gauge ground to the engine block. CHT's for 3 and 4 came down about 40 degrees with just this change. Obviously there was no CHT problem to start with... Anyway, with time to think on my hands here I'm just wondering what the collective knowledge base here recommends. Thanks, Patrick Quote
N201MKTurbo Posted February 26, 2015 Report Posted February 26, 2015 http://mooneyspace.com/topic/10087-fuel-sender-problem/ Quote
DonMuncy Posted February 26, 2015 Report Posted February 26, 2015 Make sure you understand the wiring circuit. It is a little strange, in that the power runs to the gauge and then to the terminal on the inboard sending unit (and here is the strange part) the base of the inboard unit is isolated from tank with special washers. The wire then goes from the base of the unit to the terminal of the outboard sending unit, and the base of that one is grounded to the tank. This way, the reading at the gauge is the "average" of the two sending units. Quote
Johnnybgoode Posted February 26, 2015 Author Report Posted February 26, 2015 Make sure you understand the wiring circuit. It is a little strange, in that the power runs to the gauge and then to the terminal on the inboard sending unit (and here is the strange part) the base of the inboard unit is isolated from tank with special washers. The wire then goes from the base of the unit to the terminal of the outboard sending unit, and the base of that one is grounded to the tank. This way, the reading at the gauge is the "average" of the two sending units. Is this applicable to a C? It was my impression I had only 1 sender per wing, but I'm still learning my systems. Patrick Quote
carusoam Posted February 26, 2015 Report Posted February 26, 2015 Expect the 65C to have a sensor on both ends of each tank. This is an old fuzzy memory, but it's the best I have... The more recent POH indicates that there are two sensors in each tank. There is no indication of when the factory changed from single sensors... Sounds like grounding or shorting could be a problem... Access to the sensors is a little bit of a challenge. From the interior, remove the side wall panel. From the outside it takes removing an access panel. This experience is from my old 65C... Best regards, -a- 1 Quote
Johnnybgoode Posted February 26, 2015 Author Report Posted February 26, 2015 Thanks and I'll have to investigate the 2nd sensor idea. I've seen the ones behind the side panel but haven't opened up that multitude of underwing inspection panels yet. Quote
mike20papa Posted February 27, 2015 Report Posted February 27, 2015 The old senders are mechanical rheostats. They can be smooth running for only so many decades and then they can start to hang up, until the fuel sloshes around in flight or landing and then then start "reading" correctly. If it's a ground problem they probably work or they dont. You can also rock the airplane on the ground by moving the tail cone up & down - see if the gauges respond. Good Luck. Quote
N201MKTurbo Posted February 27, 2015 Report Posted February 27, 2015 Make sure you understand the wiring circuit. It is a little strange, in that the power runs to the gauge and then to the terminal on the inboard sending unit (and here is the strange part) the base of the inboard unit is isolated from tank with special washers. The wire then goes from the base of the unit to the terminal of the outboard sending unit, and the base of that one is grounded to the tank. This way, the reading at the gauge is the "average" of the two sending units. Not trying to be a smart ass, but it is the sum of the two sensors. Quote
Dale Logsdon Posted February 27, 2015 Report Posted February 27, 2015 A 65C has only one fuel sender per tank. 2 senders per tank didn't start untill 1968. 1 Quote
wombat Posted February 27, 2015 Report Posted February 27, 2015 I recently had a fuel gauge issue that is similar to your issue with the right gauge. I sent it out to Kelly Instruments, who does quite a few repairs. They said that it was a non-fixable fault inside the gauge itself. My suspicion is that it is a short somewhere inside the gauge, perhaps part of the coil that physically moves the needle. I'm planning on getting my old gauge and tearing it apart if I can to see what's going on. My left gauge is what is broken, so maybe we can work together and create a single working gauge cluster. Quote
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