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Hi all! I bought a used 2010 FJ from the dealer about 4 months ago. I have an issue relating specifically to fuel pump replacement and fuel capacity, after the dealer replaced the pump. If this isn’t the right place for this post, please let me know where else to get better advice.

Long story short: Fuel pump was replaced. Empty fuel light comes on, I am only able to fill ~15gal before the pump shuts off. Fuel gauge shows full. But it is a 19gal tank, and before the repair I was able to fill the full 19gal. Why is it not filling all the way but saying it is full?

Long story:
Right after someone attempted to steal the driveshaft and the dealer reattached it, the following morning (July 14th) I could not get it to stay on. It would turn over for a second or two, then shut off. Battery was good and it had gas. Didn’t have much time to try to diagnose. Got it towed to the dealer, because I was still in the 3 month used warranty and figured they’d help out (hint: wrong). Apparently, the fuel pump was bad. Warranty didnt cover it, so I sucked it up and paid for them to replace it because I didn’t have time to search around for another shop and had already had it towed to the dealer. They did the work quickly, and I went to pick it up.

When I had it towed, it had maybe a gallon or two left, but the empty light wasn’t on yet. When I picked it up, the empty light was on, so I drove half a mile to the gas station and filled up. Here’s my issue. Before this repair, when I went to fill up on a low tank, I was able to fill ~18gal. It’s a 19gal tank. When I filled up after the repair, the pump shut off after ~15gal (This is in Oregon, where attendants pump for you). I thought it odd, but didn’t focus too much at the time. My fuel gauge showed that it was full (so went from empty and then some to full with ~15gal). Go about my life, and notice my mpg is worse, then remember that I only filled 15gal (so my mpg math according to 19gal is wrong, because there’s only 15gal). Next time I go to fill, I drove about a mile to the gas station once the empty light came on. (I don’t make a habit of waiting till the light comes on, but in this case I wanted to know exactly how much it took from empty to full). Same thing, pump shut off at 15.046gal and my fuel gauge showed full.

I looked online, and couldn’t find anyone with the same problem. Some other posts said maybe the float is sitting higher than before, and the empty light is coming on earlier, when there’s still gas in the tank. But the dealer didn’t put any gas in it after the repair, so it had maybe a gallon or two in it. So it doesn’t explain why I’m only able to fill 15gal but the gauge is showing full when it should only be about 3/4th.

I took it back to the dealer and had them check the work. They couldnt find anything wrong (apparently rechecked the assembly).They said they took it to the gas station and filled up (I had just filled up 3 days before, so the gauge was maybe 1/8 down). I asked if they drained it completely then filled it, they said thats not something they’d do. Okayyy, so they didn’t recreate the issue I’m having. The advisor said if it keeps happening, then I can bring it back when it’s near empty again, and they’ll take it to fill and see what happens. (I’ve already fully explained the issue, so I’m not sure if they’re not understanding or if they don’t believe me. This issue isn’t the end of the world, but considering it’s caused by a repair they did, I want it fixed by them).

I just filled again and the empty light came on as soon as I pulled up to the pump. This time it took 14.874gal, but the fuel gauge said it was full. So the issue is still there. Again, I can’t find anyone else with this same problem. I don’t know the science behind how the fuel pump fills and the sensors and gauges and whatever could possibly be causing this random issue. Does anyone have an idea of why this might be happening? I want to have a better understanding by the time I go to the dealer next, since they act as clueless as I truly am. Thanks in advance!
 

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All that's wrong is that your fuel gage calibration has been affected by sloppy workmanship during the pump replacement.

The fuel gage sending unit is attached to the fuel pump assembly, and actuated via a float attached to a stiff wire 'arm'. If whoever is replacing the fuel pump assembly isn't careful when removing and reinstalling it in the fuel tank, they can bend the wire arm and create a wildly inaccurate fuel gage indication, which will also affect the point at which the low fuel warning light turns on.

Your fuel tank is fine, and still holds 19 gallons.

Your fuel gage calibration is off, and the fuel gage doesn't accurately display the true fuel level. The low fuel warning light is also inaccurate. The float arm needs to be tweaked back into its original configuration, or better yet the whole fuel level sending unit should be replaced.

Whoever does the work needs to be someone familiar with the FJC/4Runner fuel pump/fuel gage sender setup, and competent enough to remove and replace it without damaging anything.
 

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The gauge is designed to show "E" and the low fuel light come on, when there are still several gallons left in the tank. Some folks find that is when 4 gallons are still in it (about 20% of the tank capacity). So, it is necessary to use the trip odometer to track from there, to make use of the last few gallons.
From your description, it sounds like your FJ came originally with a gauge that for some reason didn't do that. Probably when the pump was replaced whatever it was that made your gauge special, went away. It might not have been the fault of who did your pump replacement, since it was designed to work the way yours is now working.


"I looked online, and couldn’t find anyone with the same problem."
The Toyota low fuel light coming on early has been discussed in a lot of threads here. Links to a few below:

Norm "frustrated with the small FJ fuel tank AND the wonky way the gauge doesn't give accurate information" Kerr
 

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Here's a photo of the fuel pump/fuel gauge sender assembly, showing the wire 'arm' the float is attached to.

Unless care is taken during pump removal and re-installation in the tank, it is possible to bend the arm, affecting fuel gage calibration and low-fuel light trigger point.

A few years ago there was a massive Toyota fuel pump recall that affected hundreds of thousands of Toyota vehicles that use this type of fuel pump, and some percentage of these vehicles had problems with fuel gauge calibration because the float arms were inadvertently bent/deformed during pump replacement.

When I had my pump replaced under the recall, I had it done by a dealer who had replaced dozens of pumps, and my fuel gauge calibration was unaffected.


Automotive lighting Liquid Fluid Cable Lamp
 

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I am the original owner of an '07 and my low fuel light always comes on when I still have four gallons left, i.e., I can only pump 15 gallons in at that point. I always assumed that this is normal. Perhaps the old pump was the problem. I kind of like the extra warning especially if you are a great distance from a gas station. I also use my trip odo to monitor tank level. When my light comes on I know I have four gallons left and at an estimated 15 mpg, that means I have 60 miles left to drive. Don't worry about it.
 
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