Fuel Gauge is going hinkey!

[FrayAdjacent]

I had noticed over the last couple tanks of gas, that my fuel gauge seems to be showing less fuel than I should have. Today it was at the halfway mark with only 75 miles on the trip meter! (I reset it every fill up) It shouldn't even be below the 3/4 mark.

What's involved in recalibrating it? I think I'd read about it somewhere before.

(darn car has cost me a bit this year... new water pump, new belt, oil changes, need a new battery, need a new key remote... blah!)

[Lil bastard]

According to the factory workshop manual, this is done by removing the battery and tray, opening the fuel tank, removing the fuel sensor, draining the tank, adding exactly 12 ltrs. of fuel, reinstalling everything and then using a PIWIS or PST2 Tester - Select vehicle type (911 Boxster), then select control modules, instrument cluster, select menu item tank calibration, confirm calibration.

I'm not aware of any other way to do it. Btw, the manual also says that Calibration is necessary after replacement of the fuel tank, fuel level sensor or instrument cluster. If yours needs this, it may signal that the sensor may need replacing.

[FrayAdjacent]

I think I'm having more issues than just a hinkey fuel gauge...

I fill up the car every time at the pump. Meaning, I let the pump run until it stops. I do not try to squeeze in more fuel after that point, because my experience is that when the pump stops, the tank is FULL. It will overflow a little if I try to squeeze more fuel in.

A few weeks ago, I 'topped off' from a little above 3/4 tank because I was running down to Houston, and wanted to have as much fuel as I could before I left. I think the pump cut off before the tank was full, since I was expecting to put in about 2-3 gallons, and only got 1.5 or so in (iirc). I also record my fuel consumption and calculate fuel economy - and that 'tank' came out to 33mpg! I thought it may be an anomaly with the pump and went about my life.

After that fillup, I have noticed that when I fill up, the fuel gauge needle is never on top of or over the dash for Full. It's always a bit below.

Yesterday, the low fuel light came on a few miles from home. I had about 220 miles on the trip gauge (which I reset every fillup). I figured this is probably a symptom of the fuel gauge calibration issue I'm seeing. Today on the way to work, I filled up with 230 miles on the trip gauge, and put in 13.47 gallons. That comes out to a fuel economy of 17mpg!! The car's MPG gauge is showing me 26.2, which is slightly higher than the average I usually calculate. I should be hitting 24-25.

So I'm thinking something is wonky with the tank or evaporation system causing my fillups to be inconsistent. I'll have to look at data from my last fillup, but my though is, the previous time I filled up, I didn't get as much fuel in as it should have, and today, I did get 'enough' in - resulting in traveling that 230 miles on less fuel than was actually in the tank.

Saavy??

I'm about to put a new battery in the car, so I'm thinking the ECU will reset and the fuel maps will be relearned. I'm wondering if it will also relearn the fuel level?

I'm also wondering if I may have an issue that's causing the pump to stop prematurely, leaving me with varying actual amounts of fuel relative to completely full.

[Lil bastard]

A new battery may help, but I'm not sure. I say this because I store my car every year with the battery out of the car for 4-5 mos. and my fuel gauge is always accurate as soon as the car is restarted for the season.

so far as the pump cutting off prematurely, this is entirely possible. There is an issue with these cars with the hoses inside the fuel tank. It is covered in TSB Boxster 3/99 2015 2.

One of the symptoms of this issue is innacurate fuel readings. It was first discovered when owners began to run out of fuel while the gauge was indicating fuel in the tank, and when reporting some difficulty in fueling the car.

The fix is to remove the fuel tank hose assembly and, using nylon cable ties, to secure the hoses in a way that they do not interfere with either the inner flap
of the fuel filler neck or with the travel of the fuel sending unit arm and/or float.

PM me with your email, and I'll send you a copy of this TSB. It can be done DIY in under an hour...with all the usual cautions about working with the fuel tank opened, etc.

[FrayAdjacent]

Wait... I think I'm smoking crack and not knowing it!

I just looked at my recorded fillups, and I had 360 miles between today's fillup, and the previous, which would come out to be 26mpg, which seems right.

I'm pretty religious about resetting my trip meter, and I would have remembered resetting it 120 miles late... I'm confused as to what happened, or what is happening.

:|

I'll just have to keep observing. There may be no problem at all. Or at least if there is, it's the nut behind the steering wheel!