Ok so getting pretty aggravated with this issue.

Previously the fuel level gauge would act weird. With a car that has 230K miles I'd expect some wear and tear.

I took out both fuel level sensors to inspect the rheostat lines and the brass button that rides on the rheostat and found the following:
The driver's side rheostat button wasn't worn down, but the passenger side (the main) was definitely worn which would explain the eradict level on the gauge.

So I replaced both float level sensors with Nissan parts and it is acting even worse.

The spec for the Main sensor states it should have a range of 3 ohms at full and 80 ohms at empty
my replacement sensor reads 0.8 ohms full and 79.2 ohms at empty and perfect linear changes throughout the sweep of the float arm.
Off but not too far off

The spec for the "sub" sensor is 3.0 ohms full and 43 ohms at empty
My replacement sensor reads 0 ohms full and 37 ohms at empty (UPDATE: nope it reads 43 Empty)
again off but not too far off.

I thought MAYBE the main sensor's arm is getting hung up on the corrugated tube that goes to the sub tank.
But tonight with 306 miles on the trip odometer, JUST started the car, I saw the gauge go from a slightly too high of a reading for 300 miles of a smidge over 1/4 tank to 5/8th of a tank (just higher than 1/2) without moving the car. For the rest of the evening whilst using the car it still read over 1/2 tank.

we've been resetting the trip odometer after each fillup as we can't rely on the gauge. The car gets up to 20mpg so at around 350 miles we fill it up...and it has been consistently taking 17-18 gallons to fill up.

I'm at a lost as to what the problem could be.

I'm thinking of adding various resistors to the wire that is the feed for both sides' senders.

At full up the gauge is significantly higher than F, so adding resistors to the wire should bring the needle back to F.
I'd wire the resistors onto a piece of wire that has a quick disconnect (blade/socket or Pin/socket deutch type) so that I can try different ohm resistors and/or remove the resistor altogether.

Thoughts?

NOTE: when I checked the fuel level at around 350 miles, the SUB was empty enough to where the pickup tube would not draw fuel, but the main tank still had 2-3 gallons.


Curious though, it is normal to draw from the sub tank (driver's side), first THEN the main tank?
I would expect the level of both tanks to go down evenly.

Check the ground contact on the main fuel pump connector and make sure the female pin isn't burnt, that's very common from a dying fuel pump that draws too much current. It will cause the resistance to ground to bounce around, affecting the sensor but not necessarily stopping the pump. Also check pin-fits at both sensor connections, the sub and main sensors are wired in series and any bad connection in the chain will cause bouncy-bouncies.

THANK YOU so much for the tip....gives me a direction to chase.

Do you happen to know where I can get new pins/sockets that are for nissan/infitini?

Thoughts on drawing fuel from the SUB before the MAIN?

the fuel pump DOES have 230K miles on it.....sooo maybe a new pump and a new female ground pin on the MAIN electrical connector solves this problem

Nissan fuel pump connectors haven't changed much in a dog's age, there are plenty of pigtails available on eBay and Amazon:
https://www.ebay.com/itm/133154329827

Keep in mind that fuel level sensors are basically just a balance-resistor circuit. There's a fixed-value pull-up resistor inside the cluster, and then the sensor acts as a variable pull-down resistor. The voltage in between them correlates to the fuel level, and the stronger the pull-down, the lower the voltage goes and the higher the needle indicates. That's why grounding the circuit to test it-- basically applying a 0 ohm pull-down -- should make the needle go to full deflection. But that's also why a poor quality ground will make for funny readings.

Vis the system sucking from the reserve tank first, they're usually set up that way deliberately. The fuel pump motor is cooled by immersion in the fuel, so draining out the side with the pump first could have long term detrimental affects.

VStar650CL wrote: ↑

Wed Apr 13, 2022 10:57 am

Vis the system sucking from the reserve tank first, they're usually set up that way deliberately. The fuel pump motor is cooled by immersion in the fuel, so draining out the side with the pump first could have long term detrimental affects.

Thank you , again, for that.

VStar650CL wrote: ↑

Wed Apr 13, 2022 10:51 am

Nissan fuel pump connectors haven't changed much in a dog's age, there are plenty of pigtails available on eBay and Amazon:
https://www.ebay.com/itm/133154329827

Keep in mind that fuel level sensors are basically just a balance-resistor circuit. There's a fixed-value pull-up resistor inside the cluster, and then the sensor acts as a variable pull-down resistor. The voltage in between them correlates to the fuel level, and the stronger the pull-down, the lower the voltage goes and the higher the needle indicates. That's why grounding the circuit to test it-- basically applying a 0 ohm pull-down -- should make the needle go to full deflection. But that's also why a poor quality ground will make for funny readings.

re: resistors - understood...thanks for the clarification (It seems I got the eyes of the correct person to help me....yay) (no sarcasm)

I'd rather remove the female terminal, cut it off and attach a new female terminal (solder said terminal) and re-insert the terminal into the connector rather than splicing 5 wires.

They're pretty easy to un-pin, but you'll still need a fresh pin. The simplest way to get one is buy a pigtail. If you use a solder shrink, then it's only one splice and you can skip the soldering iron. Except on circuit boards, I don't think I've hand-soldered a connection in about 4 years. Those shrinks are God's gift to good wire repair.

VStar650CL wrote: ↑

Wed Apr 13, 2022 11:52 am

They're pretty easy to un-pin, but you'll still need a fresh pin. The simplest way to get one is buy a pigtail. If you use a solder shrink, then it's only one splice and you can skip the soldering iron. Except on circuit boards, I don't think I've hand-soldered a connection in about 4 years. Those shrinks are God's gift to good wire repair.

ooooh great tip

I love those solder shrink tubes !!!!