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Fuel gauge stays stuck on empty?

Tiny
DRIVERMODANIEL
  • MEMBER
  • 1999 LEXUS RX 300
  • 3.0L
  • V6
  • AUTOMATIC
  • 290,000 MILES
I pulled the fuel pump and ohms tested the sending unit to see if of the ohms resistance changes as I move the floater up and down - it does. It goes from 41.3 fully down and 3.0 fully up.
(Not sure if that's within spec, but I think it is)
I connected the pump back to the harness connector and did the same thing but looking at the gauge on the dash - with the floater fully raised up the needle on the dash moves only to half tank, and resting all the way down, it stays at the same empty reading, with the gas light on too.
The harness connector reads close enough to 12v on one of the pins with the key on ~11.34v
I jumped two pins on the connecter and the needle goes to half tank in two motions (think it's supposed to read full with the pins jumped - the 2 thin wires)
I went to the junkyard and got a instrument cluster from the same year car, connected it, and the gas gauge needle was at the exact same place as my original cluster.
I replaced the fuel pump with a junkyard unit, tested it with a multimeter and plugged it into harness like with mine, and read 41.2 down 3.0 up, and again the needle went only to half tank with floater all the way up.

Is it the cluster or the fuel sending unit/"floater"/"fuel level sensor" or something else?
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Thursday, August 10th, 2023 AT 6:08 AM

9 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,779 POSTS
Hi,

The resistance you are getting is right where it should be. I went through the diagnostics and the way it was tested is correct as well.

At the end of the diagnostics, it indicates that if the resistance is correct, to check the fuel sender subunit. I have never had that issue and of course, that is where the diagnostics stop.

I attached a pic below showing the location. Are you familiar with this component?

Let me know.

Take care,

Joe

See pic below.
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Thursday, August 10th, 2023 AT 7:19 PM
Tiny
DRIVERMODANIEL
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Okay, thank you for your answer. Here are my findings:
The harness connector read good (I believe)
11.09V key on
11.75V car on

When moving the floater manually with the harness connected, the fuel gauge on dash read 1 marker above half almost to 75% with floater in the all the way up position, all the way down resting reads empty

Ohms testing the fuel sending unit outside on bench it reads 67.3 floater down, 3.0 floater all the way up. (Not sure if within spec. Hoping it isn't)

Ps. Someone has told me to "test the instrument cluster" but I have no idea how to do that, can't find videos or write ups, would need clear instructions.
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Friday, August 11th, 2023 AT 10:18 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,779 POSTS
Hi,

The resistance in the sender is good. I attached directions below for testing the gauge/cluster itself.

Take a look through them and let me know if you feel comfortable performing them.

Take care,

Joe

See pics below.
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Friday, August 11th, 2023 AT 10:28 PM
Tiny
DRIVERMODANIEL
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Okay, I pulled the cluster out and tested the ohms resistance between the two pairs, here's what I got:
A-B 169.7
C-D 159.2
(Using a digital multimeter I placed one lead on A & one lead on B, same with C-D)
I inspected the 16 pin connector and looked perfectly fine no corrosion, cuts or black marks.
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Saturday, August 12th, 2023 AT 9:11 AM
Tiny
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Some more readings:

The sub sender harness connector (2 pin) reads:
11.21V key on
13.04V car running
The continuity between the 2 pins on the sub sender itself reads067
(Is that normal, too high?) ; Looking at the connection on the sub unit IS bent a little bit and the plastic broken.

The continuity between the wires in the main sending unit read:
041 for the thin wires adjacent each other
002 for the thicker wires adjacent each other
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Saturday, August 12th, 2023 AT 10:53 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,779 POSTS
Hi,

The readings are within spec. Make sure the connection is good and I would put some dielectric grease on it.

Were you able to check the cluster gauge?

Joe
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Saturday, August 12th, 2023 AT 8:22 PM
Tiny
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Yes, my previous reply is the "cluster gauge" you're referring to right.
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Wednesday, August 23rd, 2023 AT 8:33 AM
Tiny
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So when filling up with gas the pump clicks like if it's full. Here's the things I've done:

- Stuck a wire through the filler neck to check for blockage
- Changed out a broken "fuel tank over fill check valve" on the fuel tank & it's gasket OEM (thought this was the problem, after changing this out went back to gas station to verify and was still clicking, disconnected all the hoses associated with the canister and still clicked)
- Blew out the two hoses connected to that valve with compressed air (some white flakes came out)
- Blew air from the EGR valve (I believe is called) back to the evap system
- Blew air through the charcoal canister & vent valve air flowed through like it is supposed to (no black charcoal bits ever came out of the canister or lines)

Notes: could the issue be the small lines on the fuel tank that are clogged that I didn't blow out (yellow arrows in pic)? Could fuel system cleaner be the answer considering its been sitting for 6 months?
The previous owner before me said the car was sitting for some time 6 months before I purchased
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Wednesday, August 23rd, 2023 AT 8:37 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

Did you check the fuel tank breather tube? It's in your second pic above.

See pics below.

Let me know. Also, confirm where the breather connects and make sure there are no restrictions.

Take care

Joe

See pics below.
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Wednesday, August 23rd, 2023 AT 7:33 PM

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