Fuel gauge inaccurate

[Musikmann]

Hi friends,

I tried the search function on this sub-forum and came up empty.

My fuel gauge is not accurate. When I fill up, the needle slowly rises to the top but that is about the only time it reads with accuracy. It consistantly reads that I have less gas than I do. I realize this is preferable to reading that I have more than I do but I still find this frustrating.

Q1: What do these cars have? A fuel level sending unit, a fuel level sensor, or both? Please provide the exact name(s) and part number(s) if possible.

Q2: Where is whatever is needed located and is it a relatively simple do-it-yourself job?

Thanks in advance,

Musikmann

[white90dx]

Originally Posted by Musikmann

My fuel gauge is not accurate. When I fill up, the needle slowly rises to the top but that is about the only time it reads with accuracy. It consistantly reads that I have less gas than I do. I realize this is preferable to reading that I have more than I do but I still find this frustrating.

Thanks in advance,

Musikmann

What evidence do you have that your fuel gauge is inaccurate? Is it the final fill-up quantity of gas? What are you looking to achieve by changing the sender? It should only take a couple fill-ups to figure out how much gas you have approximately at each point on the gas gauge - why go through the hassle of opening up the gas tank?

For reference: I fill up with 12-13 gallons generally when the low-fuel warning light is on about 1/3 of the time (it likes to turn on and off in the gen2 Camry). The owners manual says the tank holds 16 gallons. I have never filled up with more than 13.8 gallons.

-Charlie

[Musikmann]

Originally Posted by white90dx

What evidence do you have that your fuel gauge is inaccurate? Is it the final fill-up quantity of gas? What are you looking to achieve by changing the sender? It should only take a couple fill-ups to figure out how much gas you have approximately at each point on the gas gauge - why go through the hassle of opening up the gas tank?

For reference: I fill up with 12-13 gallons generally when the low-fuel warning light is on about 1/3 of the time (it likes to turn on and off in the gen2 Camry). The owners manual says the tank holds 16 gallons. I have never filled up with more than 13.8 gallons.

-Charlie

My evidence is that if it indicates 1/2 a tank, I fill it up with 6 gallons and when it shows 1/4 tank it takes 9. I've also driven it down to the point when the low fuel light comes on and I don't remember even adding as much as 12 so I believe the lower the actual level, the less accirate it is. But, I certainly know how much fuel I have and at what gauge position.

What I had hoped to achieve is an accurate fuel gauge reading. If this is the "nature of these beasts" so be it. That is something else I had hoped to learn from the other gen2 owners here. If the job requires opening up the fuel tank, you have answered my Q2 that it is not a simple do-it-yourself job (at least not for me).

Thanks for the reply,

Musikmann

[Doctor J]

I will post detailed reply on this topic within next few days [I investigated related problem with my friend's camry.]

[Musikmann]

Thank you in advance Doctor J, I'm looking forward to your input.

[jasonck08]

Calculate your average MPG then just use your odometer as a fuel gage. If you can get 300 miles on a tank usually then you can tell when your getting near the 250 mark, its around the low area...

Also, on my car sometimes it will stay above full for the first 100 miles... Then it starts to drop more rapidly.

[Musikmann]

Jasonck08,

Yours is reacting as poorly as mine, just a bit differenty. Since you mentioned it, I forgot to add that the lower mine is reading, the faster it drops (especially once it reaches 1/2). Indeed, I get about 300 miles per tankful so your idea would certainly work here too.

Thanks for the suggestion,

Musikmann

[jasonck08]

Yea, mine usually reads that I have more gas than I actually do... It stays above "F" for 100 miles on average. Right now I'm about 1/3 the way down from "F" and I have gone 160 miles. It's not terribly off and I'm perfectly use to it by now, so it doesn't really bother me...

This is also how it was on my previous Yamaha 125cc scooter. It would stay at "F" for a while then drop slowly, then when it hit the 1/2 way mark it would drop quickly...

[Musikmann]

Jason,

Thanks also for the further information.

[JMSports]

Just fill it up when it says E whether its empty or not, and youll be fine.

[Musikmann]

Hey JMSports,

That's what I have been doing, pretty much. If I'm not mistaken the fuel pump is inside the tank so I rarely let the tank get less than 1/2 full due to the cooling effect of the fuel. The only exception I make to that is when I run a tank containing Chevron Techron that I want to perform it's maximum effect.

Thanks,

Musikmann

[Doctor J]

I did some calibration tests for the gauge display;
It takes about 3 to 5 minutes to react [due to gelling silicone oil inside because of the age].
I used 0 to 100 Ohm pot; set at 3, 33 and 90 ohms [full, 1/2 and empty] to do the span calibration and it seem to be working. [1 watt resistors of equal values can be used];
If the gage never indicates full, the problem is in the ground wire [brown color], that runs from the connector to the left kick panel [!]; if it has 0 resistance, the display is defective.
The low level warning light sender is thermistor not the float; when it is not cololed by the gas in the tank due to low level it conducts the electricity, causing the light to glow; as it ages it start doing this even with sufficient fuel level.

[Musikmann]

Dr. J,

That is very involved and I'm impressed! Thanks so much for the technical explanation.

MM

[drugal]

One thing you could try is cleaning the fuel level sending unit. Remove the lower part of the back seat, and you'll see a metal plate with wires going through it. Disconnect the wires, remove the plate, and below you'll find the fuel level sender. You can carefully remove it from the fuel tank, taking care to not damage the gasket.

It's made up of a float that swings up and down, moving a contact across a wound resistor. Take a soft brush and some isopropyl alcohol, and gently clean it.


Also keep in mind that the fuel gauge is not perfectly accurate, since the fuel tank has an irregular shape and uses only a single float. The fuel low light should also come on when you have approximately 1/6 of a tank left.

[Doctor J]

The most common problem with float is the 'empty spots' where the wound resistor wears the most; the wiper can momentary lose contact in these zones causing the lower reading on the gage, that goes back to normal after 10 miles of driving.