Erratic fuel gauges

GJ Humphrey · #1 07-19-06, 10:41 PM

Hello fellow sufferers,

Fuel gauges this time.

1973 T337G.

The fuel gauges lately have been erratic and erroneous. They flicker, they read wrong. They do it simultaneously, each mirroring the other. Sometimes, in flight they both read empty, even with full tanks.

Has anyone exprienced this problem. Has anyone solved it?

Thanks.
GJ Humphrey

Kim Geyer · #2 07-19-06, 11:53 PM

The first place I would look would be to pull the wing panels just outboard of the fuselage, the round ones right at the leading edge. In those holes you will find a big white plastic plug . I would clean all the pins with contact cleaner, look for corroded pins. Sometimes the pins are worn and don't make good contact. With the plugs connected, power on the plane and wiggle the wires at these plugs watching for erratic guage movement. 9 times out of 10 thats where the problem is on our airplanes.
Hope this helps
Kim

Kim Geyer · #3 07-20-06, 12:07 AM

Should have read your problem a little better. Might be a bad connection behind the guages there is a long plug that slides on and it may be loose Check the wiring at the box in the overhead.
Kim

Pete Somers · #4 07-20-06, 03:25 AM

Check all the plugs on the signal conditioner which is mounted in the roof,center panel, port side. the small white single conectors are a problem.
If not looks like the signal conditioner has an internal fault. Maybe take the case off and look for any wires off.

Pete

big al 08 · #5 07-20-06, 01:07 PM

left tank guage fluxuates between correct reading to empty once in awhile so would your suggestions be suitable for this indication? thanks rick

Pete Somers · #6 07-20-06, 01:49 PM

Hi Rick
That looks like signal conditioner problem.
Try moving the wiring to it while watching the the gauge, or tap the conditioner to see what happens.

Pete

big al 08 · #7 07-20-06, 03:59 PM

that is the one in the roof on the right side,? being stupid, what am i looking for, just wires, or what?

Pete Somers · #8 07-20-06, 04:12 PM

Rick
The signal conditioner is mounted in the roof center panel port side. The box has some adjusters for full and empty on it.
This is for the 337G and on only.

Pete

big al 08 · #9 07-20-06, 05:55 PM

thank you, have any conversation with jim in yuma? rick

Pete Somers · #10 07-20-06, 06:04 PM

Yes Rick
Sent him a email but waiting for a reply.

Pete

Richard · #11 08-17-06, 09:53 PM

Is this a 337 with the resistive senders? If so, you will note they are notoriously erroneous. I just replaced 3 ($590 each). (Makes me soooo mad too. Silly SW units that look IDENTICAL to my $25 SW unit made for MG’s)

They tend to get more inaccurate as they reach the limits of the throws on the armature. Lead and time make contact with the windings less. Not to mention the sloppy rivet that the arm pivots on.

There is a guy in Canada that rebuilds them for around $100 a piece. If someone is interested I can post his information?

KyleTownsend · #12 08-18-06, 12:32 AM

I have a similar problem with my Left gauge. I have narrowed it down to the molex connector on the conditioner box. I can flex the wires there, and the needle will go from where it should be to full. I was hoping it was the connector that plugs into the box, and had that replaced. But it's still doing it. So I guess the connector on the box will have to be replaced (or one of the pins needs to be resoldered inside or something).

Ernie Martin · #13 09-10-06, 04:03 PM

I too suffer from erratic fuel gauges on my 73 with capacitance-type senders feeding a signal conditioner (P/N C668004-0102). Because typically the guages go to zero together, we started out by tackling the signal conditioner. Found all connectors OK so we opened the box and found a component whose discoloration suggests that it's burnt (see figure below). Hard to believe that this is it, since 30-40% of the time the guages read accurately, but we'd like to change out the component. Problem is, we can't read what it is. If anyone has a schematic or knows what the component is, please let me know. Meanwhile, we're going to look at the other suggestions, namely the inboard wing connectors and the long plug behind the guages.

Thanks,
Ernie

Pete Somers · #14 09-10-06, 05:03 PM

Ernie
That is a high wattage resistor, which if you have a DVM you should be able to measure the resistance of.
I will have a look through my books and see if i can find a circuit diagram for the conditioner.

Regards
Pete

Pete Somers · #15 09-10-06, 05:16 PM

Hi All
The big trouble with trouble shooting the capacitance system is that with out a breakout box it is also impossiable to pin down the fault.
Cessna once did a box which covered all the aircraft up to the 421, however this was taken over by a Bendix test box.

Find a test box it will save you hours and hours of taking the system apart to fix the fault!

Pete