fuel problems again!!

hi every one, posted a while ago about my fuel problems (since then bent a few conrods aswell ooops) anyway having problems again with the fuel.
the engine appears to be sucking air in the fuel line somewhere, i hav,
-cleaned the fuel tank and cleared the breather pipe
-bypassed the sedimenter
- added two fairly small inline filters / with a pretty wide gauze
-changed the lift pump
-changed the filter and the filter housing (the bleed screw was buggered)
-and replaced the entire length of fuel pipe with new rubber pipe
problem seems to be after driving maybe 2-3 miles less depending on the load i put on the engine she'll lose power, then eventually splutter and conk out instead of idling. then if you try and start her up again she'll run (once the fuel is pumped through) just for a shorter distance then the same will happen again. will go a bit further if you go at low revs for a while put will not pick up again until youu stop and wait like i sauid before.
i am wondering whether it could be the sender unit on the tank, the joints are quiute corroded and i have worked around them a fair bit (replaced boot panel etc) anyone had similar problems? any help would be great cheers!

top of the sender unit the 2 metal pipes are known rust parts, try removing the sender unit and cleaning them with some emery tape to find any small holes, you can use epoxy resin to seal them or replace the whole unit.

Also, make sure the tank is VENTED to let air IN as fuel is taken OUT.

Venting arrangements vary from model to model. Some need a filler cap that is vented.

You can eliminate this possible source of bother by driving with the fuel cap OFF for long enough to find out. If the problem doesn't happen with the cap OFF, CARAMBA! Fit a vented cap - or bang a nail hole in the top of the tank.

If it does, replace the cap and look elsewhere for the cause of the problem.

The symptoms sound quite like bunged fuel filter or duff lift pump, but you say you have fixed those. If it is AIR getting in among the fuel, it might be that the tiny air-bleed vent in the fuel filter head is blocked.

On top of the filter is a return pipe. If not, don't read any more.
The return pipe should be connected back to the tank, often at the #4 injector return spill pipe. The idea is to separate air from fuel before the fuel gets near the injection pump

The banjo nut of this pipe on top of the filter allows a small amount of fuel to flow back to the tank through a tiny hole. If there is air in the system, this tiny hole will let a LOT of air pass, and send it back to the tank. Once all the air has passed, a small amount of fuel will flow back, unless the hole is blocked. Essentially it will self-bleed as you drive along, and get rid of any stray air bubbles.

If the tiny vent hole is bunged-up, system does not work, and cannot clear ANY air, and injection pump ceases to do the business.

Worth checking this out. Take the pipe off and start the engine. DIesel should drip or dribble slowly out of the open pipe fitting. If not, it's bunged up, and air cannot be released, and Bob's Yer Flip.

CharlesY

thanks, this sounds promising!! i know there is a return pipe thats on the sender unit, is that the same pipe?

oh yeah i did have a problem with the tank not venting air but since then i have cleared the pipe and that seems to be ok now

Go for the vent on the filter head now.
The more you say, the more it looks like a possible cause.

For Gawd's Sake let us all know what eventually fixes it!

CharlesY

the return pipe look like it on the fuel pump, comes out of the top at the rear and goes behind the engine? is it this pipe?

commercialmatt said:

the return pipe look like it on the fuel pump, comes out of the top at the rear and goes behind the engine? is it this pipe?

Click to expand...

Nothing to do with the fuel pump.

It's the fuel FILTER head we are dealing with.

The pipe does indeed come out of the top possibly at the rear (depends which way round it is sitting) and probably goes behind the engine.

But, think only about the TOP of the filter head.

CharlesY

which bit is the filter head?

commercialmatt said:

which bit is the filter head?

Click to expand...

Keep calm Slob... he's young and innocent ....


The filter head .... well .... it's the aluminium alloy bracket thing that the fuel filter sits under.

You can change the filter easy enough, but the filter head bit stays put with all the pipes connected to it.

They all vary from car to car, model to model, so it is hard to tell from here which one you have. It might not even be the original. Folks change them sometimes.

BUT, in principle most of them have a fuel-air separation vent, and if that stops working the trouble starts soon after.

If you can't work it out, seek someone who can take it to bits, identify the vent, and make sure it's open,

CharlesY

ah right, i have changed replaced bit, there are only 2 pipes on mine, the one from from the lift pump and the other one goes to the fuel pump. where does the return go from on mine do you reckon?

That's a bummer.
If there are only two pipes then you have no air/fuel separation system and it will suffer fast and horrible if there's a leak of air IN to the supply pipe from tank to fuel lift pump.

Remember, the fuel pump SUCKS fuel from the tank, and as pointed out if there's a pin-hole in the steel outlet pipe on top of the tank (which is very common) then a lot of AIR will be sucked in and mixed with the fuel.

Only a TEENY WEENY pinhole in the pipe can let in a LOT of air, and screw things up, or a perished or slack joint. Even plastic pipes can crack, or wear through where they rub on the chassis or clips.

Your Injection pump will cope with a little air and send it back to the tank with the return excess fuel, but the moment too much air arrives, it then cannot escape fast enough, and some will pass through to reach the intermediate pressure pump in the injector-pump, and that stuffs the whole affair in no time flat.

Make SURE your system isn't drawing air with the fuel as described earlier.

One day, find a different fuel filter head, one with an air-bleed separator, or even find an old fuel / water / air separator and fit that.

CharlesY

fingers are still crossed! but, i replaced the sender unit today and took her for a drive and as yet all is well no bubbles at all in inline filter! its looking promising! oh yeah, i also checked every jubilee clip on the fuel line (all of which were fine) but when i went to check the one on the top of the lift pump i found that the top of the lift pump wasnt screwed down tight!! (was a little unexpected!) anyway, im going to keep hoping that the problem may finally been rectified! so thanks very much for your help guys! next on the list is fitting a snorkel and wheel arch extensions so may be on for more adice then!