Suddenly won't start after recent tandem pump change

Also unlike some other manufacturers Audi never fitted either a push button nor a bulb type manual pump to prime the fuel line. There again is you ran out of fuel after the warnings then totally your fault.
 
The leak must be above fuel level when parked, for air to get in. If it behaves differently when parked on a slope, (when the fuel level in the tank changes from level ground), that would put the leak at the tank end, actually in the tank. Hence my pointing out the joints either side of the level sensor/swirl pot.
Mac.
 
johnyfartbox said:
I think that there is air being pulled into the system somewhere, even after changing the pump, the short length of clear fuel pipe still had tiny air bubbles in the fuel.
Thing is, I've no idea where else to look apart from the fuel filter housing.
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Hi John, air can get it at the smallest gap. It’s not terribly helpful but you just have to eliminate every piece of hose, every connection. One thing at a time. The one thing you haven’t checked seems likeliest. Is the tank full?
Be Sherlock.
I wonder is it feasible to use Vaseline smeared on possible leak points as a diagnostic tool?

Good luck John
 
As @George Hogg has said the smallest gap and air will get in, so small you may not detect it but it may open when hot or cold or under vibration.

There are commercial "pastes" that you can apply to the joints before sliding the rubber hose on. Personally not a fan of them as too much can cause flow issues.

Replacing 20 year old rubber does not sound a bad idea anyway, although getting new OEM may well be an issue.

Even once the air is ruled out there are still other areas that can cause poor starting such as worn camshaft of bad spray fuel injectors etc.
 
All the fuel hoses "set" in position and are hard to remove. The issue then is by removing a pipe you could indeed be introducing a leak that was not previously there. Getting to the point now if a hose is removed better to replace it than refit it even if the paste is used.

Add in the biodiesel is not as good for old rubber the problem will only get worse. Similar situation with E10 and the FSI.
 
audifan said:
As @George Hogg has said the smallest gap and air will get in, so small you may not detect it but it may open when hot or cold or under vibration.

There are commercial "pastes" that you can apply to the joints before sliding the rubber hose on. Personally not a fan of them as too much can cause flow issues.

Replacing 20 year old rubber does not sound a bad idea anyway, although getting new OEM may well be an issue.

Even once the air is ruled out there are still other areas that can cause poor starting such as worn camshaft of bad spray fuel injectors etc.
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Hi Graham. If I remember correctly it runs fine off a wee diesel tank onto the pipes in the engine bay. So the issue is “south” of there
 
Yep pretty much the same as performing a diesel purge. The actual location of the leak(s) is still elusive and there is no easy way of breaking the system down further without the possibility of adding in leaks that were not originally there.

Places to start well start from one end and work to the other probably replacing rubber as you go. Obviously any bodge on the fuel filter is not acceptable nor are obviously damaged components..

The ONLY high pressure fuel pipe is the manifold inside the head, inlet pipes on pump vacuum and fuel return at a medium pressure due to spill off from the injectors.
 
audifan said:
Yep pretty much the same as performing a diesel purge. The actual location of the leak(s) is still elusive and there is no easy way of breaking the system down further without the possibility of adding in leaks that were not originally there.

Places to start well start from one end and work to the other probably replacing rubber as you go. Obviously any bodge on the fuel filter is not acceptable nor are obviously damaged components..

The ONLY high pressure fuel pipe is the manifold inside the head, inlet pipes on pump vacuum and fuel return at a medium pressure due to spill off from the injectors.
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I agree, and if you start at the tank, the first and second joints are above and below the sender top.
Mac.
 
Thanks for all your input guys.
It's now got to the point where I will try to find someone who knows the fuel system and has the professional equipment to sort the problem out.
The car is too nice and runs superb once running to let it sit there on SORN.
A rare white TDI as well.
 
John how much have you driven the car since the work was done? In the past I have had an annoying air bubble that was stuck in the fuel filter that lasted for a couple of month before clearing. It made an annoying whirring noise as it rotated somewhere inside the filter / housing.

So what I am saying is put a hundred miles on the car then reevaluate.
 
The car has been on SORN for over 2 years now, but it was and always is driven around the estate I live on.
Just to keep things moving and such.
What I might do is book it in for an MOT, and use it while the silver one is sorted out, that's got a horrible creaking banging sound on the front drivers side which I think maybe a top mount problem.
 
I do think the car will benefit from a bit of use.

Re the other car anything on the offside front suspension including a broken spring or drop links or ARB bushes
 
I'll be crawling under mine at the weekend to do the handbrake cables, so will check out the state of the rubber fuel hoses and the fuel cooler
 
So, am I about to jinx it again by saying the starting problem is now sorted??? probably. one of the rubber hoses under the car attached to the fuel cooler was a bit 'mucky' compared to the one next to it which was bone dry, so cleaned it up, no visible damage to it but obviously had a leak, albeit a tiny one. Smeared the hose in hylomar blue to seal any non visible pin holes and the car now starts way quicker than ever before, in a split second.. everytime since!!! could this actually be 'IT'?
 
Has the OP mentioned increased brake pressure after start-up? Mine has occasionally had that. Coupled with the uphill/downhill thing that points to the pump.
 
I've just read this right through, and the similarities with the problems I have been having are remarkable.

My first question would be, when the symptoms first started (before changing the tandem pump for a new one) had you done anything to the car that the symptoms could be correlated to? Like a filter change?

To find the air leak on mine I connected the vacuum pump onto the fuel feed rubber hose where it would normaly meet the metal pipes on the engine (see below). I was getting lots of air coming through there, so that proves the leak is down stream of that point.
You can see I started using a pipe clamp to seal off the line when I was emptying the fuel pot. When putting the empty pot back on, I would create a bit of vacuum before releasing the clamp, so that there was immediately suction on the line.

1.jpg


The other end of that pipe is the outlet of the Fuel Filter housing, so next I connected a pipe to that and tried the same procedure again.
IMG_20240331_120514_HDR.jpg

You need a pipe with arund 15mm I/D for this, I happened to have some coolant pipe from my Land Rover that fitted.
IMG_20240331_120435_HDR.jpg

With this setup I was drawing clean fuel through, no air bubbles at all, so the leak was either in the filter housing or before.

So next to check the filter housing, to do this I removed the pipe from the tank to the housing and replaced it. The feed from the tank into the filter housing is the second pipe up from the bottom. With that connected to a fuel can, I was still not getting any air drawn in. So the problem was not the filter housing, which was a bit of a relief to be honest.

So this only left the line from the fuel tank to the filter housing, this was quite easy to replace running through the car and down to the filter housing with clear pipe.
IMG_20240331_170332_HDR.jpg

With this line in place there was no air getting pulled through, so this seemed fairly conclusive.

To prove the point I reconnected the feed to the tandem pump, bled the tandem pump with the return line, and then tried to start the car. After a few attempts, she started. I didn't have a clear pipe in the lines now, apart from the one from the tank to the filter housing, but she has started several times no problem.

I guess I won't be 100% until I have properly replaced that fuel line, which will be fun, but I'm pretty convinced that this was the problem.

I hope that helps :)
 
Yes but you still have not ruled out the other connections / pipes on the filter housing being a source of air.
 
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