So, Why is there 2 sending units for fuel?

There is one on the pump (passenger side)
and another on the drivers side.

I never had a car with 2 sending units before, does anyone know why they have 2 on these cars?

 

Redundant systems I suppose. Not totally sure either.

 

It's more like two fuel tanks. There is a hump in the center for the driveshaft to go through. Driver side has a sending unit and siphon hose, the passenger side has the fuel pump assembly with sending unit The internal fuel pressure regulator bleeds off to maintain 3.5 bar and sends the excess through a external venturi that pulls fuel from the driver side to keep both sides level(ish)

 

Nissan just loves to complicate some simple śhit, dont they?

 

OMG. I'm always stunned when Cleric doesn't know something. Only seen it twice.

 

I mean, they pioneered a new style weight distribution which led lots of new cars to have similar gas tank placement. What do you want?

 

While building my fuel system I got into this humped tank and I really don't like how if the anything fails or doesn't work correctly (IE: cracked siphon line, clogged venturi) your right side tank can go empty while showing probably 1/3 or so on the fuel gauge.... Not too cool for a turbo car. I seriously debated on building a spare tire aluminum return style tank but will just make sure I never go under 1/2 tank when screwing around.

 

OK, Thanks man for the explanation.

Still makes no sense though to have 2 sending units, If there is a siphon tube to feed the fuel on the one side to the other so they stay level then you should still only need one sending unit.

So which one actually feeds info to the gauge..... or do they both send a signal to the BCM and then it averages the two to get a reading or does it read only one of them????

 

I posted pictures of the gas tank below. There is one pump that is part of the sending unit on the passenger side. The one on the drivers side does work like a siphon to take fuel from the drivers side and put it on the passenger side. The level sensor on the drivers side one is so it can help maintain the fuel level with the right side. You would only need one sending unit if the gas tank was flat all around, but there is a big dip in the middle as seen below which the driveshaft runs under, which is why they use the dual sending unit so it can disperse it evenly. Both FSI send signals to the BCM using the floats and meter to get a correct gas level reading. A very common issue with G owners is the floats actually do not work correctly causing the infamous gas gauge problem. Very rarely will it be a meter problem.

 

Great, thanks for clearing it up for a dummy like me guys.

My gauge was not reading correctly and I ran out of gas the other day while it was saying I had 1/4 tank left.

I ordered a new fuel pump / sending unit and didn't know there were 2 sending units so I only bought the one.

Turns out the one Rock Auto sent me wasn't the same as the one in my car so it got shipped back.

While it was opened up I figured I would try cleaning the sending unit resister contacts and cleaned them both,

Put it back together and everything works perfect now..........so far.

(As a side note, being the dummy I am I forgot to plug the drivers side unit back in yesterday so it actually was reading "empty" after assembly....pulled the back seat back out and top cover and plugged in the plug and assembled everything again and today it is reading almost full
so it's working properly now. Took me an hour to get the seat back in yesterday, don't know what I was doing wrong but it was a bitch.....today it went right in...took maybe 5 minutes and that was to get the seat belt buckles through those tight little holes in the seat!)

 

Glad to hear it! It’s a very simple job as most mechanical issues are very easy to fix with common hand tools. I would say that the passanger side fuel pump is the only one that really has issues. The drivers side you can just pull out and put some tension on the foat to see if the meter works correctly.

 

consistency? i mean look at the fuel tank.

 

Between the D21 truck I had and this Infiniti I thought Nissan actually engineered & designed their vehicles user friendly for people to work on more so than all the other vehicles I have owned.

I mean, they didn't HAVE to make access to the fuel pump so easy, most other cars you have to drop the tank or cut your own access door in the floor.

All work I have done on Nissan's has been pretty easy.

 

I agree, the split tank kinda sucks but it is really easy to work on. I had several domestic cars that weren't as easy and required the whole fuel tank to come out of the vehicle. After my first Infiniti I haven't ever gone back to the domestic side.

 

It's to calculate MPG and MTE. The readings are averaged between the 2 units from what I understand. Volvo does the same thing except theirs are stupid hard to work on.