Bora fuel tank only filling to halfway

[Manaz]

My fuel tank senders failed on me, leaving me with a bone dry tank on the M5 when the guage showed 1/3rd of a tank left...

[Dyldo]

yeah, but this ain't happening to me. I've proven that the gauges work intermittently, but that fuel tank contents isn't in doubt as i measure based on kms. I think the tank isn't filling properly, but how to test? how to fix?

[Manaz]

Intermittent faults with them is how they start apparently. They eventually get blocked by stuff that builds up over the years - apparently you can get to them relatively simply by lifting the rear seats, it may be worth checking them out...

[Dyldo]

but what i am saying is that I think I have proven that the senders aren't the main issue, they are simply a potential secondary issue that i am not too concerned about (because i don't trust the gauges anyway). I do trust the fuel economy and therefore fuel consumption of the car, and so i go off kms per tank to gauge how full/empty the tank is.

The proof is when I have travelled 650kms on a single tank (therefore close to empty) and when i am filling at the bowser i only get 35L in roughly before it starts shutting off. I then spend a good 5-10mins bouncing the car and doing the clickety-click with the bowser trickling fuel in until i get to 40L and give up. There is definitely an issue with the tank and/or baffles or something preventing me from filling.

Can the tank itself be lifted from inside the cabin via the back seats somehow? Surely it couldn't be that simple.

[Manaz]

Oh yes, I realise not the main issue (senders won't affect how the tank fills from a bowser) - but they'll cause you other kinds of grief (like running bone dry at 90km/h on the M4 like I did! ) if they continue to claim there's more/less fuel in your tank than you think you have.

Pulling the senders out means opening two ~20cm holes in the top of your fuel tank (due to the "saddle" design, there's one in each side of the tank). That may provide you with an opportunity to have a bit of look around inside the tank to see if there's anything obviously going on (may be able to see the state of the baffles, etc).

Obviously this is something you want to do with the tank as empty as possible, out in the open or a well ventilated area, on a cold day, and not whilst smoking a cigar.

Let me check my service manual to see if it gives info on removing the tank...

[Dyldo]

right, so the senders are tabbed to a 20cm plate that i can use to peak into the tank? cool. I assume the fuel pump (ours are in-tank right?) can be viewed if the tank is dry enough too.

[Manaz]

The senders and pumps come out with the ~20cm plate IIRC.

Let me confirm...

[Dyldo]

Tank was empty again today (definitely had to be close to empty, as I had travelled 450~ kms on about 40L - could not have been more) and so i pulled in to fill up at a seldom-used servo on my way home. Ended up taking 60~L without stopping, she was thirsty.

So, this is either an intermittent blockage of whatever transfer mechanism there is between the saddle fuel tanks on the Bora, or it is a dodgy filler neck, or a problem with the bowser i use frequently.

Next tank i will fill from a completely different servo to isolate the pump issue. Not exactly scientific but i guess the experiment continues.

[Back Door Shenanigans.]

I was having a similar issue. Certain Servos will cause it to cut out and require you to fill at half the speed. Others are fine. I found BP Have been fine which is good as thats who i always buy fuel with anyway.