L322 Suspected blocked fuel breather/fuel gauge error

I have a 2009 L322 3.6 TDV8. I can't currently fill it with diesel beyond just under half full - the back pressure causes the pump to cut out and if I try and fill very slowly I actually get fuel coming back up the filler pipe and spilling out.

I suspect a blocked breather pipe is causing this - nowhere for the displaced gasses to go as they are trying to be replaced by diesel in the system - but am open to any other suggestions as to what the issue may be!

My real question is: where is the top of the breather pipe i.e. where does it vent? I can't see any obvious candidate in the fuel filler opening. My first step would be to try and get some product (something like Lucas Upper Cylinder Lubricant with injector cleaner) cleaner in the top end to hopefully dissolve the blockage.

Thanks in advance - any diagrams/photos would be a massive help.

how do you know its only half full?

Good question! I'm going by usage/fuel gauge - but I get your (inferred) point that it might be the gauge. Any easy way of identifying whether that is the cause?

drive it until you run out! carry a (full) jerry can with you!! see how many miles you cover
does the gauge move from empty to half full? what exactly happens?

Good point. I think next step is to run it for a few more miles to see if the gauge is definitely moving. I have trip on Friday which will do just that.

sirmarcus said:

I have a 2009 L322 3.6 TDV8. I can't currently fill it with diesel beyond just under half full - the back pressure causes the pump to cut out and if I try and fill very slowly I actually get fuel coming back up the filler pipe and spilling out.

I suspect a blocked breather pipe is causing this - nowhere for the displaced gasses to go as they are trying to be replaced by diesel in the system - but am open to any other suggestions as to what the issue may be!

My real question is: where is the top of the breather pipe i.e. where does it vent? I can't see any obvious candidate in the fuel filler opening. My first step would be to try and get some product (something like Lucas Upper Cylinder Lubricant with injector cleaner) cleaner in the top end to hopefully dissolve the blockage.

Thanks in advance - any diagrams/photos would be a massive help.

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The breather really only applies when the cap is on, plenty of room in the filler pipe for gasses to escape.

Datatek said:

The breather really only applies when the cap is on, plenty of room in the filler pipe for gasses to escape.

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There must be a breather active when filling though? You can't have diesel going down the filler pipe and the displaced gases coming back up it at the same time - not at the rate that pumps dispense the diesel surely??

retail pumps dont actually pump that quick, for that reason

I remember reading this some time ago

Saint.V8 said:

If previously any work has been done on the in tank pump, and the battery was disconnected with the key still in the ignition ( even if not turned), the fuel level calibration could be out as the ECU remembers the previous sensor value, and when jiggled about and moved during pump work, when you power it back up again, the level reading could be wrong!

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backinblack said:

I remember reading this some time ago

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Thanks - fuel gauge has definitely shown 100% during my ownership, and it hasn't had the battery disconnected since then

What does it show when you can't get any more fuel in?
And when you've done a couple of hundred miles?

backinblack said:

What does it show when you can't get any more fuel in?
And when you've done a couple of hundred miles?

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Shows just under half full when I can't get any more fuel in. Don't know what it shows a couple of hundred miles later - I've been working on it being a breather issue - have only been doing local trips and then repeatedly trying to top it up! I have a 140m round trip to do Friday/Saturday so won't add any more fuel and will see what the gauge does.

I think your guage need recalibrating

backinblack said:

I think your guage need recalibrating

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is that even possible on an L322!?

kermit_rr said:

is that even possible on an L322!?

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Quick google and I got this but it just says 2004 RR.

As your rig is running, run it as low as you are brave enough ensuring it is very close to empty when you arrive home. Have a spare can of fuel handy. Unlock, open a window and put your key far far away. Disconnect the battery, remove the main access panel and unplug the pump electrical multiplug. Go have a cup of coffee or adult beverage, toss the ball for the dog... etc. comeback after a good rest and plug the pump/sensor feed multiplug back in, connect your battery and start her up. This will trick the electrical system in to believing you have followed proper procedures and ensures both level sensors are bottomed/reading empty.

You can of course do the full procedure at any time... as long as you drain the tank first. I just hate messing about with fuel so always replace a pump or sending unit at empty if possible. I;ve used the above cheat on three first gen models with perfect results. One failed and that was when we learned one of the floats was sticking.

If I remember right, because its a "saddle" type tank there are actually 2 level sensors that average.
So if 1 is duff it will show half when full.

Need to look, so dont shoot me yet .

J

Ok how many litres do you actually put in.
Run it till the light comes on and check with figures.
Here will help.

J

Oh and if you're going to telly on a jerry can, make sure you have some method of getting fuel into the car, practise it

A quick update - now pretty sure this is fuel gauge related - did a one hour round trip on Saturday and the needle hasn't moved.

So I guess investigations now move to either the physical parts of that system - stuck float/s - or the electrical parts - dodgy connections??

Or it needs calibrating.