Fuel quantity sender help

[chuck459]

The right fuel quantity gage in the instrument cluster of my 1979 M20J has developed a problem.  It will not move below a half-full indication.  My shop has swapped gages and found both to be working properly.  The outboard fuel quantity transmitter also seems to be working properly.  That indicates a problem with the inboard fuel quantity transmitter which is extremely difficult to access.  My shop is not a Mooney Service Center and has never accessed this part.  They were more than happy at my decision to continue flying the airplane for a while with the hope that the sender may “unstick” and began working again.  I realize this is simply putting off a problem which is going to have to be fixed eventually.  To help me better understand what is involved in accessing this fuel sender, could someone explain the correct procedure of reaching this component.  Can the fuel sender be accessed from below the wing, or will the access plate under the wing-walk have to be opened?  Since the closest MSC is over two hours away, it would be nice to fix this problem locally.  Any ideas would be appreciated.

[DonMuncy]

The inboard senders are a lot easier to access than the outers. Pull out the carpeting on the wall at about the front of the seat. It is right there. 

[Marauder]

The right fuel quantity gage in the instrument cluster of my 1979 M20J has developed a problem.  It will not move below a half-full indication.  My shop has swapped gages and found both to be working properly.  The outboard fuel quantity transmitter also seems to be working properly.  That indicates a problem with the inboard fuel quantity transmitter which is extremely difficult to access.  My shop is not a Mooney Service Center and has never accessed this part.  They were more than happy at my decision to continue flying the airplane for a while with the hope that the sender may “unstick” and began working again.  I realize this is simply putting off a problem which is going to have to be fixed eventually.  To help me better understand what is involved in accessing this fuel sender, could someone explain the correct procedure of reaching this component.  Can the fuel sender be accessed from below the wing, or will the access plate under the wing-walk have to be opened?  Since the closest MSC is over two hours away, it would be nice to fix this problem locally.  Any ideas would be appreciated.

As Don mentioned, the inboard fuel senders are behind the carpeted lower panels. Removed them and you will find they look like this:



When removed, the sender will look like this:



You should replace the cork gasket when you put another one in. Depending on which inboard it is, it will have a different bend to it.




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[Marauder]

Also, there is a place in Lock Haven PA that refurbishes them.


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[Guest]

AirParts of Lockhaven.

Clarence

[chuck459]

Thanks everyone for their most appreciated info.  This isn’t going to be as expensive a job as I had feared.  

Chuck

[DonMuncy]

Take note of those plastic washers. The wire coming from the gauge goes to the terminal which goes through the coil in the sender to the sender body. The body is not grounded on the inboard end. The wire then goes from the body to the outboard sender, through the coil and to the body which is grounded. Thus the senders are electrically "in series", reading the total resistance through both coils. The end result is the gauge reads the average of the two senders.

[ArtVandelay]

Take note of those plastic washers. The wire coming from the gauge goes to the terminal which goes through the coil in the sender to the sender body. The body is not grounded on the inboard end. The wire then goes from the body to the outboard sender, through the coil and to the body which is grounded. Thus the senders are electrically "in series", reading the total resistance through both coils. The end result is the gauge reads the average of the two senders.

So what is the resistance when full and then at empty?

[DonMuncy]

41 minutes ago, teejayevans said:

So what is the resistance when full and then at empty?

Unfortunately, I don't remember which way they go nor the actual numbers. I saw somewhere that Don Maxwell cited the resistance values. I have a used one at the hangar, but it might not be accurate. I could check it if it would help anyone.

[chuck459]

My airport is in such turmoil due to the fires in So. Cal. I am not in the mood to start working on this problem right now.  I've taken notes on everything posted here and definitely appreciate the helpful advise.  At least I know how to proceed.  Thanks again. 

[steingar]

I once asked Don Maxwell himself how to make the fuel gauges in my aircraft indicate whether there was any fuel in my aircraft.  The reaction from the audience suggested I was far from alone in this problem.

Put another way:

Fuel Gauges!  We don't need no stinkin' fuel gauges!

[ArtVandelay]

I once asked Don Maxwell himself how to make the fuel gauges in my aircraft indicate whether there was any fuel in my aircraft.  The reaction from the audience suggested I was far from alone in this problem.
Put another way:
Fuel Gauges!  We don't need no stinkin' fuel gauges!

I have 2 words for you: tomato Flames

[Bob_Belville]

My old sender arms are shaped somewhat differently from Marauder's. See pic.

If the arm pivots near the bulkhead of the tank, as with the top unit in the pic, it is possible, in fact it happened with mine, that the bent rod hangs up on the coated nut on the inside of the tanks. In my case, the gauge indicates full until the actual level drops by 10 gallons or more. Fortunately in my case the gauge was quite accurate from there to empty.

[Guest]

I just tested a new sender in the shop.  0 ohms at empty and 31.5 ohms at full.

 

Clarence

[DC_Brasil]

Hello Everyone.

I just bought a 1990 M20J. It is doing its annual and after that we'll upgrade the avionics to a G3X panel. The shop advised us to check on the fuel transmitters as they are in a bad shape for the new modern avionics. Do any of you know how much is usually a new fuel transmitter kit for an M20J in the US (I live in Brazil)? From what I understand my Mooney has 2 in each tank and I just want to prepare in case I need o replace them.

 

Thanks.

DC

[jetdriven]

On 12/17/2017 at 6:45 PM, DonMuncy said:

Unfortunately, I don't remember which way they go nor the actual numbers. I saw somewhere that Don Maxwell cited the resistance values. I have a used one at the hangar, but it might not be accurate. I could check it if it would help anyone.

0-32 OHM.  but they are in series so, as installed, its 0-64 OHM.

 

[MikeOH]

@jetdriven

Is 0 ohm full or empty?

[Rick Junkin]

2 hours ago, DC_Brasil said:

Hello Everyone.

I just bought a 1990 M20J. It is doing its annual and after that we'll upgrade the avionics to a G3X panel. The shop advised us to check on the fuel transmitters as they are in a bad shape for the new modern avionics. Do any of you know how much is usually a new fuel transmitter kit for an M20J in the US (I live in Brazil)? From what I understand my Mooney has 2 in each tank and I just want to prepare in case I need o replace them.

 

Thanks.

DC

@DC_Brasil Looks like about $2,200 for a set of four Cies senders for an M20J. You’ll want to get these for your G3X Touch panel, especially if using the Garmin EIS.

https://www.aircraftspruce.com/catalog/inpages/ciesfuellevelsender.php?clickkey=9741909

Congratulations on the new-to-you airplane!

[jetdriven]

0 is empty

 

[MikeOH]

3 hours ago, jetdriven said:

0 is empty

 

@jetdriven

Thanks.

But I'm now very curious how the system works as the gauges themselves are really current measuring; when the master is off and no current is flowing they read zero.  Therefore, it is somewhat confusing that low resistance, which would normally be associated with more current flow, is the zero reading.  Must be how the circuit is really designed; maybe some kind of bridge circuit.  Do you know?

I'm going to dig up the Mooney schematics and see if I can understand what's going on.

[jetdriven]

0 ohms is zero.  64 ohms is full. Open circuit is offscale high 

[MikeOH]

2 hours ago, jetdriven said:

0 ohms is zero.  64 ohms is full. Open circuit is offscale high 

Yes, I understand that.  It means the circuit is more involved than I originally thought: simple series circuit of regulated voltage source, sender, meter, to ground.

I'm curious to the actual circuit implementation, that's all.  So far, looking at the Mooney schematic is just a 'black box' for the fuel gauge in the cluster (no internal detail)

[KSMooniac]

I doubt you'll ever see a circuit published from Mooney, but I'd bet a dollar it is essentially the same as a 1950's or 60's automobile system and those might be easier to find.

[jetdriven]

I believe they are Rochester senders right out of a ‘57 Chevy 

[Andy95W]

4 hours ago, jetdriven said:

I believe they are Rochester senders right out of a ‘57 Chevy 

Do you have a part #?