leak off pipes

Could someone please explain the purpose of the little leak off pipes next to the injectors on a 300tdi? From what I can see they return fuel back to the pump? But why would you have unused fuel at the injectors at this stage anyway?

The pipes on my 300tdi look in very poor condition and one appears to be split, would this have an impact on the engine and if so what symptoms would you get from a split leak off pipe?

leak off pipes return fuel to pump , this is because pump is running at a certain delivery rate for a given engine speed , when engine speed slows ( foot off throttle ) the fuel in that has left the pump needs to go some where , hence spill pipe . Injector need a certain pressure to work ( lots of PSI )fuel needs to be over supplied at all times to enable smooth and instant acceleration , again spill pipe needed . think im right . I know the practice putting it into words not easy though .!!!!!!!

The fuel system is a continuous loop -excess diesel from the pump and the leak off pipes returns to the tank-the whole system needs to be air tight ie no leaks.If you have an air leak in any of the lines,fuel can syphon back to the tank making starting long winded as fuel has to be primed again-if your leak off pipes are perished or holed,change them.I have renewed mine using aquarium air line as a temp fix

The symptoms would be diesel leaking out over the engine and floor, the MPG would also suffer.

Easy and cheap to fix, just pull of the pipe, cut a new piece the same length and push back on. 3.2mm braided fuel hose works fine, about £3 per meter on ebay.

Mine split, symptoms were poor starting and a slight smell of diesel when i got home, as said, just buy pipe on ebay (1/8" ID - 3.2mm x 7mm) ie here linky.

I know it's a bit old this thread but I came across it whilst doing a search after having the same problems and replacing my heater plugs....

each banjo has two connections which go to either the next cylinder or off to the tank/pump or wherever it goes OTHER than the cylinder nearest the bulkhead. This cylinder only appears to have one connection and the other seems to be open, should there be something blanking that??

My problem, I later found, was that the heater plug which disintegrated took out the 60amp mega fuse.... I replaced that and it appears to be working now.

I think you will find that the one that appears open is actually blanked off (otherwise diesel would be leaking out), though the same about mine when I first go it

which line would you put the non return valve in ?
would it be the supply line from the tank to the filter housing or the from the filter to the pump ?? .
reason for asking my disco has the same fault i.e some mornings it will start fine heater light out touch key and away fine other mornings go out let light go out and you have to turn it over until it primes and then away it goes .
starts fine every time if I park it facing down hill if parked facing uphill for say a hour you got to let it turn over for a while .

Basically you need a couple of metres of fuel pipe with an internal diameter of 3.2mm then just measure each piece one at a time then pull that one off and replace each in turn. Job done. I've also been advised to fit a fuel non return valve into the main Diesel pipe after the filter to stop fuel simply flowing back into the tank from the feed pipe. I'm not sure how much use that is but got one off eBay for £2.45 and it's on its way.

hodge911 said:

which line would you put the non return valve in ?
would it be the supply line from the tank to the filter housing or the from the filter to the pump ?? .

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Between the filter and the throttle/injector control unit I would suggest.

cept for a 300tdi change "pump" for lift pump and "injector control" for injection pump.

timtheenchanteruk said:

cept for a 300tdi change "pump" for lift pump and "injector control" for injection pump.

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I know, I already had this diagram from when I was first looking at a dual tank veg oil setup last week. I think the names get closer as I go through the diagrams

Talking of non return valves, I ordered 6mm ID, hope this was right but thinking it could be 8mm now!

You shouldn't need a NRV, just fix the original fault.

I've added the mother of all ground straps today then started it and it started first time so hopingi have fixed it after all.

Thought this was about the injector return pipes.
The same airline that is used on the p38 air suspension works well. You may heat the ends a bit with boiling water before pushing on. Advantage of the nylon line is that it should last a very long time and is impervious to bio and veg.