Highly pressurised fuel tank!

Hi all, long time lurker first time poster in need of help

Got a strange problem, my diesel tank is getting under a LOT of (positive) pressure, quite a force when you take the filler cap off. I’ll list what’s happened so far, hopefully one of the great minds on here can piece this all together.

1994 defender TDI300

Started losing power a higher speeds, pulled fine in lower gears and at slower speeds but was lucky to get above 35 or 40 mph. Always started fine with no smoke etc.

Over the next couple of days the problem got worse, engine would run fine for up to a minute and then lose all power and almost stall. After 10 seconds or so of spluttering it would regain power and I could spurt forward again!

Finally it gave up altogether and got to the point where I had to limp in first gear at tick over revs and crawl along.

I did a lot of searching (thanks to the good people of these forums and google) and changed the fuel filter, no difference.

Though it might be the lift pump so changed that, again no difference.

So, here is my gut feeling, for some reason either not enough fuel is getting into the fuel filter before the fuel pump empties it, or air-and-fuel is being pumped into the fuel filter. If I take the bleed screw out of the air filter no diesel comes out no matter how long I leave it ticking over and if anything there is a slight inwards pressure if I put my finger over the hole.

The latest symptom it a pressurised fuel tank!

Does any of that point to anything obvious to anyone here? Or are there any simple tests I can apply to narrow things down a little.

Here’s hoping.

Change your filler cap for one with a breather.
That will allow the fuel to be replaced by air in your tank.

does it run ok without a filler cap on?? Obviously don't go driving round without it as diesel spills are lethal, but will it tick over and rev? if so the tank must have a blocked breather

Thanks, the filler cap is the same one that's always been on, its the standard locking cap (I thought that was vented?)
Sorry I should have said I've tried running it without the cap on and it still has the same problems but without the tank pressurising of course.
When I pump the lift pump should I feel any resistance? the leaver feels as free as it did before I connected it up.

the lift pump should have resistance as it is trying to push fuel through the system. Sounds like you need to replace it - you have symptoms of fuel starvation.

I'm hoping its not the lift pump as I've just replaced it, but I agree its not looking like its doing much.
The original one I took off feels like it still works so was thinking of de-gunking it and sticking it back on. Place your bets now on how many times I drop that right hand bolt this time!

Kipling said:

If I take the bleed screw out of the air filter no diesel

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THANK God 4 that ! else you would be in the sh*t !! Sorry
Is the lift pump ON cam? Have you put the pipes on the WRONG way round ?
Have you blown the feed from the tank to the fuel filter back to the tank?
DID you fit a NEW lift pump? or the one that the p/o chucked in the back of the truck when he changed it ?
You can hear if lift pump is working in your hand ! should sound like a strangled Duck + you should be able to feel it suck if you put your finger over the inlet pipe!
Also check that you have tightened EVERY thing back up

Steve

#Steve HaHa yeah diesel in there would mean I've got something very wrong!!!
I hope I've not mixed up the pipes, that would be an embarrassing first post
Is it possible to fit the pump with its leaver under the cam rather than over it? that would explain it not pumping - would it physically fit that way?

The new pump is completely new, the old pump feels ok and leaves a nice oily ring on my tongue when I test it
I'll blow some compressed air down the pipes tomorrow - I thought there was a non return valve on the tank out-pipe?
I'll put the old pump back on tomorrow and hope for the best.

Your new pump could also have a mis shaped cam arm. I had that once, did my head in trying to figure out how it pumped fine in my hand but refused to fitted to the block. It was impossible to bend it to a different shape so it was obviously made wrong.
I wouldn't have thought that would pressure your tank though.
There is no non return valve at the tank, it's part of the lift pump.

You won't be the 1st & you won't be the last to get them the wrong way round(ask me how i know)
On your Tongue should HURT
IF the l/p is good it should bleed the system WITH OUT opening the bleed screw on tick-over(mine duz)
Don't think it's possible to get the l/p arm UNDER the cam(views may differ)
Guy not so many post's ago blew pipe back to tank & said filter in tank was blocked & has run with no probs since So worth a try

Steve

Over use of emojis make the post a pain to read! (Just my personal opinion).

Magicgrotto said:

You won't be the 1st & you won't be the last to get them the wrong way round(ask me how i know)
On your Tongue should HURT
IF the l/p is good it should bleed the system WITH OUT opening the bleed screw on tick-over(mine duz)
Don't think it's possible to get the l/p arm UNDER the cam(views may differ)
Guy not so many post's ago blew pipe back to tank & said filter in tank was blocked & has run with no probs since So worth a try

Steve

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Yeah, I remember that, he said tank filter had a snot coat and had changed/cleaned it ...

Well, good news and bad.
The bad news is the old pump must be shot, the vacuum it pulls is only week (hence the tongue test) and it doesn't sustain it.

The good news is the old landy is now working, its was a case of the loose nut between the steering wheel and the seat

Magicgrotto said:

Have you put the pipes on the WRONG way round ?

Click to expand...

It turns out the new pump works fine as long as you connect the pipes the right way round

I'm embarrassed to say I'd got them reversed, and I was so careful too! Time to hang my head in shame and hang up my spanners.

Thanks for all the help guys

Kipling said:

I'm embarrassed to say I'd got them reversed, and I was so careful too! Time to hang my head in shame and hang up my spanners

Click to expand...

That won't happen It's a landy
Been there done that ! Got the T/shirt
Glad you got it sorted

Steve

Just make sure you have fitted a Delphi lift pump as anything else is just crap and won't last.

cheers, It is a Delphi pump, I even waited longer for delivery to get a genuine one, which is not like me at all normally!

Yeah worth the wait for the Delphi one anything else just doesn't last.