Here's what I did:
• I pulled the fuel pump and 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 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.

(Someone has told me to "test the instrument cluster", I don't know how to do it, I couldn't find any video or write up, I would need clear instructions)

99 RX300 290k

Is it the cluster or the fuel sending unit/"floater"/"fuel level sensor" or something else??

 

See if you can get hold of the electrical diagram. Armed with that you can diagnose better.

The problem may come down to a bad connector or ground.

Salim

 

There are two fuel senders. The connector for the one in the picture is for the "main" sender. The sub sender has 2 pins.

This might help: https://www.clublexus.com/forums/rx-...e-problem.html

 

Awesome ... This thread has all the info needed and somehow I did not think of this thread.

Salim

 

I forgot about it too and was surprised to find I posted in it. Well, it's been a while.
The link I posted then is no longer good but if you search for "rx300 electronic fuel injection pdf" you will find one somewhere.
Or you can buy the nice service manual CD on RockAuto

 

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

 

Body Electrical manual says

Fuel main sender resistance between pins 1 & 2:
Full: Approx 2 ohms +/-1
Empty: Approx 38.7 ohms +/-1

Fuel sub sender resistance between pins 1 & 2:
Full: Approx 2.0 ohms +/- 1
Empty: Approx 71.3 ohms +/-1

 

So it's off 4.2 ohms "empty" for the sub unit, that's the biggest discrepancy here. Enough to be the cause, the answer to this problem?... Hopefully

 

Apparently 2.6 ohms off spec as well considering your "+/-1 ohm" you sourced, with the main unit, is that really enough to be considered bad/faulty? Am I missing something here?

 

Don't know. Search for "RX300 body electrical (BE) pdf", lots of good information there

The problem you are reporting is "fuel gauge stays stuck at empty" and in one of your tests you got it to half way up.
Based on the picture in the thread I pointed you to these two senders are wired in series to ground, and at "full" the total resistance through both of them is 4 ohms +/-2. At empty 110 ohms +/- 2
You should be able to connect your ohmmeter to the input side of the sub sender and to ground and measure the resistance.
I'd be surprised if just grounding the sub sender input wire didn't make the gauge point full

The BE manual says there is a 16 pin connector (connector A) on the back of the combination meter.
Testing A15 - Ground it says "full: resistance 4 ohm" and "empty: resistance 107 ohm".
So that would test from there through the senders

After that the other thread shows the resistance at the receiver side in the cluster

 

Ok 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.

 

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
(From the other post linked here the guy says the thicker wires are "fuel pump positive and negative", and the thin wires are "fuel level wires")

 

OK, you tested the receiver side and the resistance numbers look good. While you were looking at the 16 pin connector did you test the pin 15 to ground resistance with the two senders at full & empty?

As for the senders, don't know about thinner and thicker wires. It's just pins 1 & 2 on both.

I gave you the resistance numbers at full & empty. So if by "The continuity between the 2 pins on the sub sender itself reads067 (Is that normal, too high?) " you mean "The sub sender resistance is 67 ohms", that would be normal if you are holding the float close to empty, and way high if you are holding the float close to full.

 

[QUOTE=maxSteel;11559152]

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


-

 

I assume your issue has nothing to do with the fuel gauge.

When you pump gas into the tank the same volume of air needs to come out.
The filler neck is split with a hose going down to the tank and the other hose also goes to the tank but is designated for air to come out when the fuel is pumped in. Please make sure that air escape path is clear.

Salim