Fuel gauge acting weird....where should I start looking?

The other day I fueled up my truck (ouch) and on the way home noticed my tank was readying down almost 1/4 after only driving 18 miles. I stopped and checked for fuel leaks but found nothing and figured that maybe the fuel nozzle just clicked off without fueling the tank all the way and I didn't notice.

About a week later, I am driving the truck again and I see the fuel gauge is now below 3/4s after only 22 miles total...and right before my eyes, I see it creep slowly to half....then, a minute later, it slowly rises up to just below full... the correct reading based on actual milage.

Do we suspect it's the gauge cluster failing or the sender? Is there any way to test?

 

Mine does that. I’m assuming it’s the sending unit. In the gas tank.

 

Yes. Almost all modern tanks use a float system with variable resistance as the float moves up and down its post.

You can measure the resistance on the float at the known tank level using a DMM. Not sure about testing the gauge, but I'm sure you could probably look at FSM for the resistance range and feed the gauge resistance across that spectrum of values to see if it sweeps right.

Could just be your float was temporarily stuck.

 

Testing the sender is one test. For your year, pin 1(Blk/Red) & 2(Yel/Red). With your roughly full tank, you should see Approx 3 Ohms.

 

Trouble with mine is it’s intermittently faulty

 

I haven't seen any of the pumps out of our trucks in person yet. Many I've changed in the past have a simple steel slide the float travels up and down on. Some have a magnet in the float itself I've heard of corrosion, and even tank floaters getting jammed in the float.

But it's also possible there's a dirty trace on the back of the gauge, or with how tasty the fuel lines at the filler neck are, and the wiring sheaths, could be rodents ate through. Tough to say.

Best option is, when you see the gauge registering way lower than expected, test the resistance on the float/sender combo. I can't explain how to do it, though. Just that it should be possible.

 

I wonder if any of this relates to mine? Mine seems to drop normally till just below 1/4 left and then stops moving. I ran out of gas a few months back because I thought I still had almost a quarter tank left

 

Crappy part is, I don't think I've seen a single modern setup where the sender isn't integrated with the fuel pump, so removal for trucks means popping off the bed or dropping the tank.

 

Yes, it's a float arm that slides across contacts on a printed board,I replaced the fuel pump last winter and got a good look at it.

A stuck float doesn't make sense though...because I watched the needle on the gauge drop to half a tank, from 3/4s, on what was almost a full tank. A stuck float would read higher than what it was as the fuel level dropped, or stay stuck low after refilling....this showed the level actually dropping by almost half a tank, and then going back up.

 

The 3rd Gen issues are making their way to the 1st gens it seems.
https://www.tundras.com/threads/fuel-gauge-issue-2022-tundra.108412/#post-2793623

 

True, that specific case sounds more like a wiring/power issue, or a bad/failing sender to me.

 

My 2000 Access Cab V8 did the same thing several years ago with the fuel gauge going up and down slowly and randomly. It probably did it 4 or 5 times over several weeks. I would also smell gasoline when I would get out of the truck. Given that you likely have to lift the box off to get to the fuel tank, I did not jump right into fixing it. It's now been several years since this happened and it has not happened again.

I guess it fixed itself.....

 

On an access cab you have to drop the tank, the fuel tank access port is actually under our cab, not our bed. I guess I will wait and see if it happens again.

 

I noticed while looking at diagrams for an '02 for another member, there was two separate part numbers for a "Fuel Sender" which were not part of the pump. Is the sending unit separated from the fuel pump on some years? Most modern trucks I've owned and changed FP out on had it integrated. Knock on wood, haven't had to do my 1GT yet.

 

Yes, the pump is a separate part, on the 2000's at least, which attaches to a plastic 'chassis' which has the sender on it. The pump itself is fairly cheap, even OEM. The sender unit much less so.

 

I think your truck has a rare case of sticker shock, 1 look at the gas prices and the old girl went into convulsions.

 

Well, I think I figured it out.

After running a few tanks through it, I find the same behavior, at the same point in the fuel gauge.

My theory is that there is a dead spot in the sender, and when the fuel level reaches that point ( at about 7/8ths) of a tank, it gets no signal, and takes that to mean no fuel, so the needle starts dropping, until the fuel level falls, or the truck tilts, etc, to get past the dead spot on the sensor and then it acts normally afterwards.

 

Any chance you can emulate the condition, but filling ~7/8 tank, then jacking up either side of the vehicle to shift the fuel load in a way that would make it register +/- a couple of gallons and watch if the needle drops out, then comes back up?

Would suck if it's a bad sender, if the sender is integrated into the pump as someone else may've eluded to.

 

Sender is absolutely part of the fuel pump 'chassis', I had it out last winter to replace the fuel pump, which is a separate part, but all part of the same assembly, and the sender part is a lot more expensive than the fuel pump part.

And yes, I could do that fairly easily. I live on a steep hill so I can tilt the truck by 15º front to back just by moving it a few feet one way or another. Good idea.

 

Yesterday, mine a 2018 was just below half. I stopped to fill up. I drove away and noticed it was still at the same spot - just below half.
First time this has happened. Like it was stuck.
I drove a few miles and then watched it drop fairly quickly to E. I toggled the steering wheel button and it showed 3 kilometers to empty.
If I hadn't just filled up I would have been concerned.
About 20 mins later when I slowed down and did some wider sharp turns I happened to look at the gauge and it showed full now.
Strange.
A couple years ago when doing about 50 mph it started dropping to the point it told me to fill up.
10 minutes later it went back up.