Fuel Gauge/Fuel Sending Unit issue

[sleepycruiser]

1964 FJ. My fuel gauge hasn’t been working and it is driving me nuts….I ran out of gas over the weekend….oops!

I grounded the fuel sending unit and the gas gauge goes all the way to full and I read that means it is the fuel sending unit…so I think the gauge is working? I replaced the fuel sending unit (83320-35020) and the gauge still doesn’t register the tank. It stays all the way empty.

What else could it be?

 

[charliemeyer007]

My 72's gauge has never worked right. It stays full+ for a very long time, E is I'm walking. I put a 12.5 Datsun B210 gallon aux tank behind the rear axle. I bought an assortment of small 2% resistors from radio shack to change the Datsun range to Toyota. I managed to get the gas gauge to read from 1/2 to E when I put the switch to read the aux tank. With 30 gallons on fuel on tap and 25 mpg I was way tired of driving before I ran out of gas.

My odometer is a better indicator of gas range in normal operation. In like low range low then I switch to aviation mode and use the stop watch for gallons per hour calculation.

There are threads about the voltmeter being the 7V power supply for the gas gauge.

My favorite fuel gauge - the bent coat hanger with a cork float poking threw the gas cap on the J3 Cub, direct read in level flight. Oh and it had an ArmStrong starter too - pull the prop or you better have enough altitude or speed to wind restart it

 

[sleepycruiser]

The only other thing I can think of is that the ground wire might not be grounded to the gauge?? I haven’t pulled the dash gauge to see what runs to the back yet.

 

[sleepycruiser]

Saving this thread for this weekend.

Fuel Gauge Wiring - Help Verify

I'm installing autometer gauges in my cluster to replace amp, temp, and oil stock gauges. I'm keeping my fuel gauge but in doing this I've build a new enclosure for my gauges and not using the factory circuit board. Can someone help validate the terminals on the fuel gauge so I don't...

forum.ih8mud.com

 

[Engineer8000]

The sender has to be grounded.

 

[sleepycruiser]

The sender has to be grounded.

I checked and it is grounded with the existing ground wire. I checked for continuity between the ground screw and fuse box ground and that tested ok. What is weird is the positive tab has ground continuity on the new sender, but the old one doesn’t. Neither work so not sure….ugh.

 

[fjwagon]

This is typical, not good seems to happen, I usually clean the terminals, at both ends. I would also clean the ground terminal at the chassis as well. I've had this problem several times. Boggles the mind why it just one instrument stops working on the cluster. I usuaully mess with it to get going. I checked the sending unit for resistance when it first happened. I checked in the full position and it had zero ohms which is mormal, in the empty position it had the correct ohms as wel( don't remember the value), anyhow, I also checked for dead spots or gaps but couldn't not any so I deemed the sending unit good. My suggestion: just make sure you have good connections on the whole circuit not just grounds.

 

[Engineer8000]

The early senders are point type regulators, not variable resistors. It could be at rest, the points are closed. It's been a while since I messed with one of those.

 

[45Dougal]

Are you sure that you bought the right sender for your instrument?
If you ground the signal wire at the sender and it fully deflects, then there's nothing wrong at the gauge end.
Testing for continuity is always misleading because it can have a wide resistance range. Testing resistance is much safer, but in this case is also meaningless because of how these old ones work - follow the test in the manual.

 

[sleepycruiser]

Are you sure that you bought the right sender for your instrument?
If you ground the signal wire at the sender and it fully deflects, then there's nothing wrong at the gauge end.
Testing for continuity is always misleading because it can have a wide resistance range. Testing resistance is much safer, but in this case is also meaningless because of how these old ones work - follow the test in the manual.

Yes. The early models are non-existent.

CityRacer said it would work when I emailed them, but I found one local. I’ve found on MUD where others made it work…only diffetence is the plate.

OEM Fuel Tank Sending Unit for '66 to '72 Land Cruiser FJ40 FJ45

OEM fuel tank sending unit for '66 to 9/'72 Land Cruiser 40 Series. Compatible with F engine. Gasket and screws are available separately.

www.cityracerllc.com

 

[Engineer8000]

cityracer is telling you fact, that is the regulator type sender. the float changes the metal diaphragm position with level.

 

[sleepycruiser]

cityracer is telling you fact, that is the regulator type sender. the float changes the metal diaphragm position with level.

Correct. I’m going to deep dive into it tomorrow. I lost patience and ran out of time today. I need a beer.

 

[sleepycruiser]

I pulled the new sending unit out and turned the 40 on…and I was seeing if the gas gauge would move as I manually moved the float. Moving the float all the way to where it would notate the tank as full showed the pic below. Curious I put the old sending unit back in and it did the same when I manually moved it. Now I’m wondering if it is the gauge, but when I ground either sending unit to the ‘positive’ terminal the gauge goes all the way to full. I have no idea.

 

[45Dougal]

Ok so either your voltage regulator in the gauge needs cleaning / adjusting (quite likely), or alternatively it could be that the float stem on your sender needs bending so that when the tank is full, the sender is under more pressure.

 

[sleepycruiser]

Ok so either your voltage regulator in the gauge needs cleaning / adjusting (quite likely), or alternatively it could be that the float stem on your sender needs bending so that when the tank is full, the sender is under more pressure.

Here is the inside of the fuel gauge.

That’s like be strange that both sending units needed to be bent?

 

[Engineer8000]

No voltage regulator in the early gauges, it is in the sender.

 

[sleepycruiser]

Not sure what is going on. I cleaned all the connections. Made sure there was continuity from the top of the sender to the back of the gauge. It also seems like those connections are common with the ground…which is probably the problem. I guess I should have run a separate wire to see if that helped, but the entire sending unit plate is grounding to the sending unit ‘positive’…not sure why/how.

 

[45Dougal]

No voltage regulator in the early gauges, it is in the sender.

Ah yes sorry.. the teeth in the hole is for gauge sensitivity adjustment though?

 

[45Dougal]

Not sure what is going on. I cleaned all the connections. Made sure there was continuity from the top of the sender to the back of the gauge. It also seems like those connections are common with the ground…which is probably the problem. I guess I should have run a separate wire to see if that helped, but the entire sending unit plate is grounding to the sending unit ‘positive’…not sure why/how.

Measuring "continuity" using a meter is misleading because the resistance of the sender can be less than the threshold for continuity. When this is the case, you'll read continuity between the sender wire and ground because its connected to ground via the sender.
The same is true for any lighting wire which is grounded via a bulb which is only a few ohms when cold.
This is why I always recommend using the ohms setting.

I'd disconnect the sender wire at the sender, and at the gauge, and measure the resistance between the two ends - it should be around zero ohms. Some corrosion at intermediate connections could be part of the problem.

 

[Engineer8000]

I think these have zero and span adjustments like most gauges.