Fuel Sender/Gauge problem

[Pinecone]

OK, thought we knew what was wrong, but now what.

When I picked up my plane, I noticed the right fuel gauge was reading just under the 27 mark, when the tank was full.  Once the fuel level was down, it read fine.

So, took the plane in for annual and mentioned the issue.  They checked and the outboard sender was sticking, so they sent it for repair.  Shop fixed it and tested it.

It was installed, but still the same issue.  The repair shop thinks it may be an issue with the inboard sender, but then would read properly when half for more, but not for lower quanties.

Maybe the gauge?   If so, how repairable?  

1986 252

[ArtVandelay]

Since it’s a resistance sender, a bad connection could result in bad readings, need to check the wiring, each section including the connectors and make sure connections a secure and clean.

[N201MKTurbo]

I suspect your inner sender is grounded. The senders are in series. The wire from the outboard sender is connected to the flange of the inboard sender and the flange for the inboard sender must be isolated from ground. It is isolated by using transistor insulating washers on the 5 screws. The ring terminal from the outboard sender must be under one of the insulating washers. The insulating washers are available from Newark. The part number is in the parts manual.

https://www.newark.com/abbatron-hh-smith/2535/washer-bushing-nylon-6-6-6/dp/94F8985

These guys actually have them in stock:

https://www.masterelectronics.com/en/abbatron-hh-smith/2535-11499565.html

[Pinecone]

Not sure how it could be the inner one, as it works fine and accurate from 26 to empty

 

[N201MKTurbo]

9 minutes ago, Pinecone said:

Not sure how it could be the inner one, as it works fine and accurate from 26 to empty

 

There is nothing wrong with the sender, one of the mounting screws is improperly installed and it is grounding the inner sender, cutting off the signal from the outer sender.

[Pinecone]

OK, so you are saying the current it going through the inner sender, then to ground instead of going to the outboard sender THEN to ground.

That makes sense.

Thanks