Fuel Sender Wiring M20K 252

[Pinecone]

How are the fuel senders wired?

I seem to recall hearing that they are in series.  So gauge to inboard sender to outboard sender to ground.

The issue is, my right side setup does not read higher than about 25 gallons on the gauge.  The left side reads full, when full.

The right side, once the fuel burns down, reads normally and accurately.  Left works fine.

At the annual, the shop found the outboard sender was binding at about half travel, so it was sent out of overhaul.  But that did not fix the issue and did not change how the gauge reads at all.

If they are wired as stated above, I would suspect that the system is grounded between the inboard sender and the outboard, basically bypassing the outboard sender.

 

[carusoam]

Sounds like the sensor went from not working properly…

To not being connected properly when it got back…

Or whatever was binding in the beginning is still binding now….

 

It must be really challenging to reach in the tank and move the float up and down…

But, from the outside of the tank… the float/sensor is easily removed to test its operation…

 

You almost have the minimum excuse to buy a set of Ceis fuel level sensors, if desired… 

If this is a Ceis gauge already… there we’re a few Mooney tanks that needed a different bend…

Ceis is really good at determining and remembering the details….

 

PP thoughts only, not a mechanic…

Best regards,

-a-

[DonMuncy]

The wire going from the inboard sensor to the outboard one is (supposed to be) insulated from the inboard sensor by an insulating washer on the inboard sensor. You might check to make sure that is the case. Better yet, use an ohmmeter from that wire to ground. If zero ohms, no insulation. If some low ohms, but not zero, it is acting right.

[Pinecone]

Thanks.  That is what I was thinking.

Would there be any resistance if the outboard sender is fully down (no fuel)?

[carusoam]

Expect that they fail to zero… if the wire breaks.

If they failed to full… that would be incredibly misleading…

Best regards,

-a-

[Pinecone]

I understand that.  My question was, if the tank is low, will the outboard sensor read 0 ohms or a small resistance.

If 0, then some fuel will have to be put in to get the float off the bottom.

[carusoam]

PP guessing only, let’s invite @M20Doc to stop by… (fuel level sensor question… functional check)

 

The long bodies are more simple fuel tank wise…

The tanks are one big long rectangular shape…

Holding 50gal on each side..

The outer FL sensor hits the bottom regularly…

There may be no fuel seen at the filler cap, with several gallons still in the tank…

A sure sign the float uphill… is adding zero voltage to the pair of readings…

As the volts go up, resistance goes down, FL needle climbs…

As volts go down, (as when there is no electricity), FL needle hits the bottom…

I surmise… as the floats sink their resistance increases towards infinity to make the voltage drop to zero…

 

Stand by for somebody with better knowledge to arrive…

 

We can also invite our Ceis guy to drop by…  he can be really helpful sometimes…

Best regards,

-a-

 

[Guest]

The inboard fuel transmitters are supposed to be insulated from contacting and grounding on the tank.  Ground is provided through the outboard transmitter.  There are supposed to be 5 nylon bushing on the screws on the inboard transmitter.  Allowing the inboard transmitter to find ground would render the outer one useless.