Fuel Gauge always shows full

[boybach]

I thought I'd asked about this issue before but I couldn't find anything in the archive other than an old post from 2021 that didn't really address this s

No matter if I switch tanks, the fuel gauge on the dash always shows a little over full and never moves, ignition on or not.
I'll be heading over to the coach today, was planning on having a go a tracing the fault - is there a fuse for the gas gauge? All other (temp/oil pressure) indicators work fine.

BTW I hear an audible click outside the coach when switching from main to aux tanks.

Any tips as to fixing the problem?

Thanks

Larry

 

[RF_Burns]

I thought I'd asked about this issue before but I couldn't find anything in the archive other than an old post from 2021 that didn't really address this s

No matter if I switch tanks, the fuel gauge on the dash always shows a little over full and never moves, ignition on or not.
I'll be heading over to the coach today, was planning on having a go a tracing the fault - is there a fuse for the gas gauge? All other (temp/oil pressure) indicators work fine.

BTW I hear an audible click outside the coach when switching from main to aux tanks.

Any tips as to fixing the problem?

Thanks

Larry

Larry,
A constant Full reading usually indicates an Open circuit to the fuel senders (Constant Empty points to a short to ground in the sender line). On the back of the Main/Aux switch are 2 tan wires (one with a double white stripe), these goto the fuel tank senders. The grey/double black stripe wire between them on the switch goes to the gauge.

Check that the connector on the back of the Main/Aux switch is fully seated.

- next pull that connector off the switch and use an ohm-meter to test the resistance to ground on both tan wires. You should get a reading of 90 ohms or less on each one. If you do, then the issue is between the switch and the gauge.

- If you get something well over 90 ohms, then back under the coach near the tank selector valve there is a connector with the tan wires. Check that the connections inside are not corroded.

-Next check that the fuel tanks are grounded to the frame. You should read near zero ohms between the tank itself and the frame.

 

[tmsnyder]

-Next check that the fuel tanks are grounded to the frame. You should read near zero ohms between the tank itself and the frame.

Or 0v with the key on

 

[pvfjr]

When both tanks show an incorrect reading, I like to troubleshoot this from the dash switch. Follow Bruce's instructions for checking the senders above, but since both of them give the same behavior, I'd lean toward checking the gauge.

If you unplug the switch, the harness has two sides to it. One side, circled in red, has two wires for switching valve power. The other side, circled in teal, has four wires (three pins) for gauge switching. The center pin is the output to the gauge (gray/black) and low-fuel-switch circuit (green, if equipped). Turn your key on, and ground that gray/black wire out with a jumper wire. Your gauge should move to 'E'. If it doesn't, you have a gauge issue and don't need to mess with your tanks.

If the gauge test passes, and you get <90 ohms for tank readings following Bruce's instructions above, then you have a switch problem. They can be carefully opened up, cleaned and given fresh dielectric grease when needed. I like to clean contacts with a Euro-tool fiberglass scratch pen found on Amazon.

 

[pvfjr]

@boybach to answer your other question: no, the fuel gauge does not have its own fuse. Oil/temp/fuel are all powered by the IGN wire on terminal F in the diagram above.

You could be having loose-pin connection issues with terminal C on your gauge PCB though. I made a video going over this issue for dash lights, but you could possibly be having the same issue.

 

[boybach]

I thought I'd asked about this issue before but I couldn't find anything in the archive other than an old post from 2021 that didn't really address this s

No matter if I switch tanks, the fuel gauge on the dash always shows a little over full and never moves, ignition on or not.
I'll be heading over to the coach today, was planning on having a go a tracing the fault - is there a fuse for the gas gauge? All other (temp/oil pressure) indicators work fine.

BTW I hear an audible click outside the coach when switching from main to aux tanks.

Any tips as to fixing the problem?

Thanks

Larry

The one upper brown shows 88 ohms but the bottom wire reads open OL on meter. After cleaning one of the connectors at the switch I now have the AUX gauge registering. It takes a minute to move, but it does eventually register full, moving away from the "pinned" overfull position. Once I switch back to main, the needle immediately pins.
I was a bit rough in the weather dept today so I didn't get under to look, but with my very amateur electrical skills I'm guessing there's a connection problem at the 2 wire connector near the tank selector?

Larry

 

[werewilfs]

@boybach to answer your other question: no, the fuel gauge does not have its own fuse. Oil/temp/fuel are all powered by the IGN wire on terminal F in the diagram above.

You could be having loose-pin connection issues with terminal C on your gauge PCB though. I made a video going over this issue for dash lights, but you could possibly be having the same issue.

I'm jealous of that access to the area behind the dash. If only we could just pop that windshield off easily.

 

[pvfjr]

I'm jealous of that access to the area behind the dash. If only we could just pop that windshield off easily.

Popping it out is very easy! Especially compared to putting it back in.

 

[pvfjr]

The one upper brown shows 88 ohms but the bottom wire reads open OL on meter. After cleaning one of the connectors at the switch I now have the AUX gauge registering. It takes a minute to move, but it does eventually register full, moving away from the "pinned" overfull position. Once I switch back to main, the needle immediately pins.
I was a bit rough in the weather dept today so I didn't get under to look, but with my very amateur electrical skills I'm guessing there's a connection problem at the 2 wire connector near the tank selector?

Larry

Ah, so you had two problems! It seems you've sorted one of them.

For the remaining tank, it could be either connector 10, connector 2, the sender connection, the sender itself, or the tank ground.

 

[boybach]

Ah, so you had two problems! It seems you've sorted one of them.

For the remaining tank, it could be either connector 10, connector 2, the sender connection, the sender itself, or the tank ground.

My money is on a connector, 50 years down there under the coach, well .... we'll find out tomorrow.

BTW, where is the tank selector located relative to the rear wheel?

thanks

Larry

 

[RF_Burns]

My money is on a connector, 50 years down there under the coach, well .... we'll find out tomorrow.

BTW, where is the tank selector located relative to the rear wheel?

thanks

Larry

Tank selector valve is on the inside of the driver's side frame rail ahead of the cross rail in front of the front (AUX) fuel tank. Look for two fuel lines going into it from the back side and one fuel line coming out towards the front of the coach. Power is a single black electrical wire.

Unless of course a PO has changed things, then all bets are off!

 

[boybach]

Tank selector valve is on the inside of the driver's side frame rail ahead of the cross rail in front of the front (AUX) fuel tank. Look for two fuel lines going into it from the back side and one fuel line coming out towards the front of the coach. Power is a single black electrical wire.

Unless of course a PO has changed things, then all bets are off!

Located the plug, opened it up and because of the limited amount of room to work (coach sitting on grass) all I was able to do was give it a shot of MG electrosolve 409B, then replug. Going back to dash, I now had the spec resistance on both tan wires and gauge appears to be working for both tanks - it's pretty hard to tell though, as tanks are full. Nevertheless, the gauge doesn't pin like it did before so I'm calling this a win for now. When I get the coach up a bit higher I'll open up the plug again and give the terminals a thorough cleaning. Thanks for all the help

Larry

 

[tmsnyder]

Located the plug, opened it up and because of the limited amount of room to work (coach sitting on grass) all I was able to do was give it a shot of MG electrosolve 409B, then replug. Going back to dash, I now had the spec resistance on both tan wires and gauge appears to be working for both tanks - it's pretty hard to tell though, as tanks are full. Nevertheless, the gauge doesn't pin like it did before so I'm calling this a win for now. When I get the coach up a bit higher I'll open up the plug again and give the terminals a thorough cleaning. Thanks for all the help

Larry

As long as you have confidence in your selector valve, you can always drive until it sputters, switch to the other tank and start looking for gas (in most parts of the country) , you'll have about 7-8 gallons so 50 - 60 miles to get to a filling station. JWID sometimes, and my gauges do work ok.

 

[boybach]

As long as you have confidence in your selector valve, you can always drive until it sputters, switch to the other tank and start looking for gas (in most parts of the country) , you'll have about 7-8 gallons so 50 - 60 miles to get to a filling station. JWID sometimes, and my gauges do work ok.

I thought what I might do to test the valve is to switch to reserve tank and start the engine and run it for a while?
OTOH I suppose if the valve isn't operating and stuck on the main tank, that wouldn't prove anything though, right?

Any definitive tests?

Larry

 

[Bhart]

I thought what I might do to test the valve is to switch to reserve tank and start the engine and run it for a while?
OTOH I suppose if the valve isn't operating and stuck on the main tank, that wouldn't prove anything though, right?

Any definitive tests?

Larry

Take a drive for 150 miles and see if the gauges change.

 

[boybach]

Take a drive for 150 miles and see if the gauges change.

I'm pretty sure the gauges are working now, just asking how to test the valve to see if it does actually switch tank source.

Larry

 

[tmsnyder]

I thought what I might do to test the valve is to switch to reserve tank and start the engine and run it for a while?
OTOH I suppose if the valve isn't operating and stuck on the main tank, that wouldn't prove anything though, right?

Any definitive tests?

Larry

They act as one tank for the first ~34 gallons, so you'd have to run it for a 'long while'

 

[boybach]

They act as one tank for the first ~34 gallons, so you'd have to run it for a 'long while'

Oh. I thought there was a test where you could hold the valve and feel a "click" while a helper moved the switch back and forth? I saw a pic of the OEM valve posted by @JSanford last year, but under my coach there looks like there's another type there, possibly a FV-1T?



Larry

​

 

[pvfjr]

I thought there was a test where you could hold the valve and feel a "click" while a helper moved the switch back and forth?

You can definitely do that. It should having a decent sensation of a click/thunk inside. It's not 100%, but it'll let you know whether or not it's completely dead.

You can also pinch off one of the input lines while the coach is running. If the coach dies, switch tanks and see if it can stay running. If it didn't die within a few moments of pinching off the line, then switch tanks and see if it dies.

If you can't find a difference in performance between the two tank selection positions with one of their lines pinched off, then the valve isn't doing its job.

 

[boybach]

You can definitely do that. It should having a decent sensation of a click/thunk inside. It's not 100%, but it'll let you know whether or not it's completely dead.

You can also pinch off one of the input lines while the coach is running. If the coach dies, switch tanks and see if it can stay running. If it didn't die within a few moments of pinching off the line, then switch tanks and see if it dies.

If you can't find a difference in performance between the two tank selection positions with one of their lines pinched off, then the valve isn't doing its job.

Just what I needed, thanks a lot.

Larry