Starved or out of fuel?

[bobski]

Annoying problem today in our Superb (TSI11.

My mother in law borrowed the Superb with the trip computer showing 90kms to empty. About 10ks in, car loses power, she pulls over and it won't restart. I come down in the ute and try to restart it. It semi starts and dies over and over. And eventually its just cranking. Pretty much all the signs of having no fuel, but the trip computer is still showing 80kms to empty and the gauge is halfway to a quarter of a tank.

So I put 20 litres of fuel in from a jerry can and it cranks about 5 times and starts. No problem since.

So all signs point to something wrong with the fuel reading and the tank was just empty. However, and this is whats got me scratching my head. The odometer is showing 595km since the last fill (we religiously reset it). We normally go 600-650k's and refill when the light comes on (yeah not best practice, but with two toddlers stopping for fuel isn't always at the top of the list).

Opinions? Could the car be using more fuel than its calculating? Maybe some scum on the bottom of the tank? Its due for a service in a month or two, so we might just fill at 500ks until then.

[Umai Naa!!]

Fuel pump on it's way out?

[alexaescht]

Fuel pump failure or in-tank filter clogged

[2009fsi]

Mother-in law drives with a heavy foot?

That range reading is calculated as fuel left in the tank at current consumption. I've seen the figure change markedly, depending on how I'm driving at the time. An indicative figure, possibly only meaningful for flat road feather foot drivers, at best. Very few fuel pumps scavenge the last litres from the tank efficiently. I know my old 3TV6 would go almost to the last red fuel gauge indicator & then take about about two litres less than stated tank capacity. The thing is, it must have had more than 2 litres in it then, because a full top up includes about 2-2.5 litres in the filler pipe, capacity not counted in stated tank capacity. I wasn't in the habit of ever allowing it to run that low though, because all tanks end up with some residue & condensation in the bottom, even plastic ones.

The other factor when stuck on the side of the road is, the angle of the car to true horizontal.

[bobski]

Thanks for the advice. My mother in law is no where near a lead foot. Maybe the car got bored and tried to commit harikari?

I'm leaning towards a temporary clog as it makes the most sense (if I can call it that). I don't know much about the warning signs of a fuel pump going, but seems weird it'd start working when I put more fuel in. I've been kicking myself all night, I should have taken it straight to a servo and brimmed it as that would have ruled out an empty tank. I'll do that tomorrow, but in the meantime, the car has done extra k's.

It died on on a flat surface. I've actually run this car down to 10kms left in the tank when I forgot to stop in on the way home (40k round trip into town). It took 55 litres I think as I remember thinking "oh, there's still 5 litres in the tank". In this case, based on the readout and K's done since the last fill, I'd have expected the tank to still have around 12 litres in it which is quite a bit. Anyway, hopefully the fuel pump, because I imagine a fuel system clean isn't covered by warranty.

[Alf01]

Possibly water in the fuel. The new additional fuel dispersed it. Don't use E10 crap, it's really rubbish, but maybe filled up at a fuel station that ran it's tank down and hadn't cleaned it for a while.

[bobski]

Possibly water in the fuel. The new additional fuel dispersed it. Don't use E10 crap, it's really rubbish, but maybe filled up at a fuel station that ran it's tank down and hadn't cleaned it for a while.

Interesting theory! Its always filled at Caltex with premium. I took it for an absolute belting because - you know - I'm sure that'll help. Running perfectly. Also filled it up and worked out there was *at least* 10 litres in the tank so that rules out gauges being incorrect. The wife is not happy, don't blame her, she will be pissed off if she gets stuck between home and town (not to mention its a bit dangerous on some sections of our road to pull over). It didn't go down well when I said I thought the dealer will have little clue as to the cause.

[bobski]

So the outcome was after a visit to the dealer was.... *drum roll* ... They don't know.

Checked the car thoroughly and found a loose negative wire on the battery and some rats had been nawing at some foam insulation (I knew that and have killed said rats). That at least confirms they opened the bonnet hah.

I understand where they are coming from - pretty hard to diagnose after the fact if nothing was logged. My wife wants me to write to Skoda about it so they at least know. It is a bit dodgy having the car lose all power at speed, but its run fine ever since... It had also run fine up until the incident. So... I suppose I have a nice bridge to sell myself?

https://www.youtube.com/watch?v=fm2W0sq9ddU

[brad]

I had a Nissan Bluebird do a similar thing after 3 years of faultless running. Totally died halfway through a 80kph corner. It then ran faultlessly for another 3 years.

[bobski]

Same thing happened yesterday. We've been just filling up before it gets below 100km and had all but forgotten about it. yesterday, with an indicated 75km on the way to get fuel and wouldn't start, again took 50 litres to fill. If I didn't know better, I'd say I have a 50 litre fuel tank instead of a 60 litre Back to dealers next week, won't take "we don't know" as an answer. I have videos, pics etc as proof this time. Interestingly, the videos show that the needle and km to empty didn't update when I added 5 litres.

[Mysticality]

I started my RS one morning and backed out of the garage - the engine slowly lost revs and puttered out... No CELs, no nothing. Started it back up and it was fine again.
Maybe they all do it once.

[Guest001]

Vacuum lock in the tank Maybe I really dont know but have heard of some cars getting that.

[bobski]

Vacuum lock in the tank

I've had vapour lock before and it recovered (different vehicle).

It still has 10 litres of fuel, which is quite a bit. I'm leaning towards a fuel pump issue inside the tank. The interesting thing I noticed after rewatching the before/after video was that the fuel gauge didn't move when I put 5 litres from a petrol can in (it was sat on about 1/8 of a tank before and after). Maybe its a simple setup issue? Car settings set for 50 litre tank... I assume thats electronic even though the float is mechanical?

This guy gives a pretty good run down on the in tank fuel pump.

https://www.youtube.com/watch?v=5hTNWo3E4nE

[bobski]

Scarily, this has happened again while my wife was sitting on 100km/h on a highway (with over a quarter of a tank). Which is just what we've been worried about. :/ Thankfully she was able to stop safely and the car restarted immediately. I'm not particularly happy, its getting dangerous, but hopefully Skoda can sort it for good.

Skoda have looked at my Superb and believe its the fuel tank level sensor and are getting a replacement. This somewhat gels with the fuel gauge not moving when I put fuel in after the last breakdown. However, it doesn't gel with if it thinks it had an 1/8th of a tank, definitely has 10 litres, but wouldn't start?

Question for the brains trust.
I'm no mechanic, so possible dumb questions - but surely this sensor isn't responsible for allowing fuel though??? Wouldn't that cause many faults like this one? Shouldn't it pump fuel if it has it (possibly engine protection?)? I know VW went through that whole "sudden deceleration thing" before and I haven't followed what happened after that hit the headlines, but now I'm in that situation I'm wondering if we are seeing it?

[woofy]

I had a fuel sensor play up for 12mths and it turned out the apprentice hadn't plugged it back in its socket in a Mazda 323 we had when they changed the fuel filter which was under the rear seat. They literally smacked the guy in the head when they found that. But in the case of that car it made no difference to running just was ****y when fuel got low in being accurate. Who knows what kind of systems these have though as they are much more complex, it might have some fail safe, you'd want the diesels to so they don't have to be primed if that run out.