B4 wagon TDI fuel starvation

My B4 wagon now has 140,000 miles

I have been noticing for a while that if I accelerate at full power that the engine starts to cut out at just above 4000rpm.
If I rev the engine in neutral, or drive at high revs but not accelerating hard then the engine goes cleanly right up to the rev limiter as it should.
It seems then that the tank can supply enough diesel for almost full power, but at 4000rpm at full power I think that the pump starts to starve and so the engine cuts out.
I changed the fuel filter and it made no difference.
Then last night the car quit completely in the fast lane of the M25
Luckily I was doing 80mph and managed to coast across all three lanes and onto the hard shoulder.
The fuel gauge was shoing almost empty but not completely.
I had a 5 litre can of diesel so I put that in, and then the car restarted so I drove to a filling station and filled it.
I only got 65 litres into the tank, so when it quit there was still at least 5 litres still in there.
When I got home I changed all four rubber leak off pipes on the injectors because years ago an old Audi 80 TDI that we had did a sort of similar thing when they perished, but it hasn't made any difference.
Also I looked at the clear line from the filter to the pump and there are no bubbles.

What could cause the motor to quit with 5 litres still in the tank and also prevent full flow of fuel at full power?

Are there any extra filters on the tank or something?

I suppose that there could be a blockage in the tank. You may also want to check the line from the fuel pickup to the IP to see if some sludge built up in it. I'm not sure how you could check it, but you could just blow it out with compressed air (after removing it from the tank-end & plugging that outlet).

The fuel pick up has a molded plastic strainer mesh at the lower end. This strainer may be partially blocked by the DERV dirt that has accumulated over the years. Run the tank down to about 1/2 or lower and remove the float pick-up to examine it. The bung is below DERV level with a full tank, so don't try this topped off.
There's a check valve in the line so blowing air to back flush may not be possible with this valve in place.

how do I get to it?
is there an access panel in the boot (trunk) floor or something?

There is an access panel in the boot. It's a round black metal plate with 3 screws in it, then there's about a 10cm plastic threaded ring that holds the fuel pickup/level sender in.

I've also seen the check valve, Lug Nut mentioned, partially clog. Replace it or put a coupling in it's place.

Oops, didn't know about the check valve. May want to gently blow into it from the tank end of things, if at all.

I took the pickup out today and it looked like new.
It has a sprung loaded telecoping section in the middle which according to Haynes is to make sure that the pickup is pushed right to the bottom of the tank.
If this is true then I would expect to have to push down against spring pressure slightly to do up the retainer but that doesn't happen. The pickup just drops into the tank and sits there...

Where is this check valve?

The check valve is in the fuel delivery line on the exterior of the tank just an inch or two from the connection pipes on the bung.

i assume that it's purpose is to stop fuel flowing back to the tank in case you have a small air ingress leak
if so then you don't need it if you don't have any air leaks
I'm quite tempted to get new rubber hose all the way from the tank to the fuel filter

http://forums.tdiclub.com/showthread.php?t=68872&highlight=fuel+sender

check out the 10th post on this forum. it has pictures on what to do. I had a similar problem, and drilled out both fuel sender and return lines, not a problem since.

And how does an A4 fuel sender relate to the B4?

You're right the check valve stops the supply line from draining back if you have a leak, change the filter or open up the fuel system for some other reason. Mine was restricted and causing an air leak so I replaced it with a coupling until I got a new one. I never got a new one.
I would replace the check valve before the whole line.

take the check valve out--and forget about it--unless you park on a severe hill--it was meant to keep the fuel from draining back under that condition-------mine totally plugged--then stuck--on a b4 wagon----sooooooo

Ideal setup would be to install an electric transfer pump and omit the check valve.

And allows electric priming of the fuel filter at replacement time, too!

tried to mount a ford 3-5 psi pump in the tank--as i run 66% wvo---worked for a few pumps--and they would stop?????????? sooooooo--took one apart--guess what--the 66% wvo would get under the brushes--and no contacty---too thick oil mix!!!!!!!!!!! so--if your going to use only pure diesel in your tank--or bio--you may get away with it-----it fit right down thru the tank hole---and i put a wire to the back with a relay and fuse---

I looked on the parts database for this non return valve.
I don't see it.
Can anyone tell me which part it is?

The check valve menioed is part of the fuel pickup assy in the tank. It's integrated into the assy.

It's late, otherwise i wouldn't be so lazy as to not look for you...but if you do search, there is a write up (i've seen it!) on how to remove the check valve.

HTH

Tony

TonyJetta said:

The check valve menioed is part of the fuel pickup assy in the tank. It's integrated into the assy.

Click to expand...

Lug_Nut said:

The check valve is in the fuel delivery line on the exterior of the tank just an inch or two from the connection pipes on the bung.

Click to expand...

The picture isn't too clear but it's Item 12. Item 9 is the return line check valve.

john be right--its not in the tank---

I stand corrected! I must have been thinking about the A4?

Sorry for the confusion.

Tony

And TonyJetta is also on the A4 kick, like jjohnv, ignoring the A3/B4 heading of this group of messages.

John Beyer said:

The picture isn't too clear but it's Item 12. Item 9 is the return line check valve.

Click to expand...

I'm afraid that 9 and 12 are rubber hoses. They connect the metal pipes to the top of the tank.

I suspect that the non return valve is a US spec item that my Euro spec B4 doesn't have.