Replies to This Discussion

Permalink Reply by david shrader on January 14, 2016 at 3:28am

Is it constant? When you top off do the gauges read at the same spot every time? Do the gauges start showing fuel burn at some point? If so, I'd say the arms on your sending units are set (bent) a little too high. If not maybe you can give a little more details...

Dave

• ▶ Reply

Permalink Reply by Marvin Penepent on January 14, 2016 at 7:03am

I had 3 gal. left after a flight in the right tank and 6 in the left. The gauges read just above 3/4 after filling the tanks up it did not move. When I shack the plane or fly the gauges do not move. I have checked the grounds, and the power to the gauge and tested the sending units at the gauges. I got a remote camera for Christmas but I can not use it to look in the tanks. I have tried to use a light and mirror but can't see anything. 

• ▶ Reply

Permalink Reply by david shrader on January 15, 2016 at 1:13am

I would start at your senders, it sounds like there not moving..... Float, sender arm incorrectly bent, arm stuck in one position due to rubbing. I know you don't want to hear it but you gotta get eyes on the sender arm/float to see if it's actually rising an falling with the fuel. If the senders are actually working, then ohm them out at low fuel level and high fuel level (there will be a big difference, something like 2ohms to 10oms) if your senders remain the same there's something wrong with your sender.
With all that said I have a feeling you have some kind of wiring issue. The odds of having two sending units doing exactly the same thing is almost impossible. Sender wire to "s" terminal, power to "+" terminal, an ground to ground terminal, I'm sure you already know this. Lastly the body of the sender needs a ground, the easiest way to check this is to jumper off one of the senders mounting screws to ground. After all these words I'd say check the sender ground first it's a common problem.

Dave

Ps if my explanation is confusing say so, I'll try again

• ▶ Reply

Permalink Reply by Marvin Penepent on January 22, 2016 at 5:33pm

UPDATE on my Fuel Gauge problem.  Today I saw the floats. The float is in the inside end of the tank about half way between the front and back of the tank close to the cockpit. With the fill cap at the other end about halfway or more from the front of the wing. with the dihedral in the wing I have 6 gal at the fill point and full at the float. Now I have to fly it to almost empty to see how it will read. May have to change to some other type of senders and gauges to get a good fuel readings.

• ▶ Reply

Permalink Reply by david shrader on January 23, 2016 at 11:46pm

I'm sure there is a 601 specific solution to the dihedral gas level problem. On piper navajo's there are 2 senders in series in the tank, that way the resistance is comming off both senders one at low side of the tank an the other at the high side of the tank. It would take some playing around with the senders an a gauge that had the proper range to make the duel sender setup work but it's doable... Side note, the garmin G3X will set a fuel curve off any resistive type sender which would make a duel sender setup very easy

Dave

• ▶ Reply

Permalink Reply by Mark Maltais on January 23, 2016 at 3:41pm

Welcome to the world of Zen senders... Do a search, you'll find many a thread on these pieces of junk... :(

• ▶ Reply

Permalink Reply by david shrader on January 24, 2016 at 12:26am

Mark I'm sorry you've had issues with your fuel quantity indication. The VDO senders are the same in design as what you would find in most general aviation aircraft. The care with the way there installed is what makes the difference. The caravan has 4 resistive senders for one tank which makes it very accurate but a pita to install. I'm not trying to start anything just pointing out that the VDO senders are not that bad, they will preform well if installed with care. The sender that always caused me trouble consistently is the capatance type sender. Advice to anyone installing a sender in a tank: set the sender arm, install sender in tank, make sure you install a good ground from sender body to airframe ground, hook up gauge an set angle of tank to equal dihedral, add gas an see if you have leaks an if gauge is reading correctly.... If not reading right adjust the arm on the sender... Wash rinse repeat till it's acceptable.

Dave

• ▶ Reply

Permalink Reply by John Austin on January 24, 2016 at 7:41am

Dave makes some very good points! When I built my 750, it never occurred to me to adjust the sender arm prior to installation. The result was that one sender's float bottomed-out on the tank bottom before the other and therefore the reserves at empty weren't the same.  My EFIS allowed for calibration of the senders, but I still had to have a higher reserve than I wanted in both tanks so they would read equally at "empty." Remember that even if you  bend the arms perfectly, the tanks are hand-made and vary slightly. Just a few degrees difference from vertical in the side-wall of the tank where you mount the sender makes a big difference in where the arc of the float travels!

I think most of the problems with VDO senders is that some are not genuine but rather "VDO type" aftermarket parts from third-world vendors and the quality varies - what you get is "luck of the draw." Mine have been fine for 350+ hrs and 3 1/2 years ... the only problem I had was an improper ground which was my fault!

John

N750A

• ▶ Reply