Suddenly won't start after recent tandem pump change

No, I don't think so, in fact I know it doesn't.
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That's the fuel level gauge
 
Also if you zoom in on the black rubber ring it looks squashed more at one side than the other and slightly out of shape. What sits on that?
 
The black things is a float valve which allows fuel into the sender chamber. As the fuel is used up it opens up to let more fuel in. The chamber in the sender is like a swirl pot, so that you don't lose fuel when you are going up steep hills or around corners. You can see it operates an opening on the side with a rubber seal. :)
 
DaveySprocket said:
The black things is a float valve which allows fuel into the sender chamber. As the fuel is used up it opens up to let more fuel in. The chamber in the sender is like a swirl pot, so that you don't lose fuel when you are going up steep hills or around corners. You can see it operates an opening on the side with a rubber seal. :)
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If the float valve doesn't open, and no fuel gets into the swill pot, then you'll suck air. If the level of fuel in the tank, around the swill pot rises, (by filling the tank, or parking nose down), then fuel flows over the edge of the swill pot regardless of the float valve, no problem.
Mac.
 
PlasticMac said:
If the float valve doesn't open, and no fuel gets into the swill pot, then you'll suck air. If the level of fuel in the tank, around the swill pot rises, (by filling the tank, or parking nose down), then fuel flows over the edge of the swill pot regardless of the float valve, no problem.
Mac.
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Just stick the clear tube, that you attached to the sender, into a pot of diesel. If it pulls clear fuel, it's the sender.
Mac.
 
johnyfartbox said:
Did that yesterday, no start but pulled the fuel up no problem. did you mean the input pipe on the tandem pump ?
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Yes, straight pipe from the diesel tank, or container, to the tandem pump inlet. If that draws clear fuel, no bubbles, it'll take a bit of cranking, fuel/air flowing over the mesh, into the pump, air being cleared via the return, to purge the air already in the pipe. But if the flow is clear, it strongly points to the sender being the source of the leak. At least it does to me, but I'm not a diesel guru, (understatement).
Mac.
 
Here is a copy of a guy on Facebook who is having the same problem with air in the fuel supply on his TDI A2.
I asked him what is the problem with his sender unit because he was asking if anyone has one for sale as he's convinced it's the sender unit causing the problem.
Here's his reply.

John .
Morning, from the out let of the fuel supply from the sender unit it it drawing up air. I've run a clear pipe directly from the sender unit to the engine compartment with a temporary inline filter. Checked and replaced all the fuel pipes from the filter housing to the fuel cooler and they're fine. But from the feed of the sender unit it is drawing up air bubbles. Also put the clear feed pipe directly into a separate fuel container and there's no air. Put it back on the sender unit and there's bubbles.Everything is pointing to the sender unit. Regards.

Thoughts guys?

Someone suggested replacing the O ring, I'm assuming that they mean the large one that the sender sits on when it's dropped into the tank.
 
johnyfartbox said:
Here is a copy of a guy on Facebook who is having the same problem with air in the fuel supply on his TDI A2.
I asked him what is the problem with his sender unit because he was asking if anyone has one for sale as he's convinced it's the sender unit causing the problem.
Here's his reply.

John .
Morning, from the out let of the fuel supply from the sender unit it it drawing up air. I've run a clear pipe directly from the sender unit to the engine compartment with a temporary inline filter. Checked and replaced all the fuel pipes from the filter housing to the fuel cooler and they're fine. But from the feed of the sender unit it is drawing up air bubbles. Also put the clear feed pipe directly into a separate fuel container and there's no air. Put it back on the sender unit and there's bubbles.Everything is pointing to the sender unit. Regards.

Thoughts guys?

Someone suggested replacing the O ring, I'm assuming that they mean the large one that the sender sits on when it's dropped into the tank.
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Reassemble the sender.
Block the connections to the sender, with the exception of the outlet.
Connect a clean tube to the sender outlet.
Put the sender in a bucket of water.
Gently blow into the tube, you'll see bubbles out of the bottom, but, maybe also you'll see bubbles from the leak. If possible, block the bottom inlet, (where fuel would normally enter, but bubbles are coming out). Blowing will 🤞reveal the leak ...
Mac.
 
johnyfartbox said:
Really? a bucket of water !!.
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I don't see a problem with water, but I'm not looking at the parts, just looking for a way forward. (Although I've suspected the sender assembly for a while).
Any liquid will do.
Even better, if you can block the bottom inlet, add food dye to the water, and suck on the tube. This would be better, as it mimics the way it works, the leak being inwards, a vacuum leak.
I wouldn't think the water will harm the level sensor, after all, it's in diesel normally.
Alternatively, just replace the sender assembly with a new one. I'd be suspicious of second hand, as your co-sufferer, on FB, shows, it may be a more common fault than imagined.
Feel free to consign this post to the bin, if appropriate. No offence will be taken.
Mac.
 
No offence taken mate, I was just wondering if water would damage the fuel level electronics.
A bucket of diesel would be more appropriate though a tad more expensive 😛
 
johnyfartbox said:
No offence taken mate, I was just wondering if water would damage the fuel level electronics.
A bucket of diesel would be more appropriate though a tad more expensive 😛
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I'd say diesel is best to test with & if you put the Sender in a bowl it can be poured back & not wasted.
If you have a hand vac pump at least you won't get a mouthful 🤮 & it will hold the vac for longer & you can also see what is happening better.
Not sure if and how much a replacement sender's are but it does seem as if you have narrowed it down to that area.
 
Hopefully yes, I have a choice of two other A2s where I could try the sender and O ring but I'm scared I might cause the same problem on those.
 
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