Fuel filter problems again

[Head Womble]

Help guys, the disco is going through fuel filters again.
 I was using cheap crap, but swapped over to MANN filters last year, over winter I was running dino (don't ask), as soon as I filled up with bio the filter blocked, this was swapped for another MANN filter that has lasted just 700 miles.

 Now what has me stumped is when I took it off it was not full of fuel, as the disco has a lift pump before the filter how is air getting into the filter causing running issues yet when a new one is fitted all is ok.

 the lift pump is working (pumps fuel from the outlet when cranking), but air is still getting in.

 I'm thinking the ally casting of the filter housing may be porous allowimg air in when the filter starts to block.

 Any other ideas ?

[Julian]

I've run on Britpart £2.50 filters for years and never had a problem.

Air could be getting in before the lift pump ... have you check the sedimenter ... conveniently located on the inside of the chassis rail above the rear axle?

Can't remember the exact problem, but I lent my neighbour a length of griflex hose to bypass his sedimenter and said I'd like it back once he'd cleaned the sedimenter out.  It cured the problem and guess what, I've never seen the hose again.

Fuel pipes on the tank outlet corrode sometimes and I've seen rusty pickup pipes in the tank.

Got a fuel filter body and a fuel pickup / sender unit (just needs the fuel gauge wire re-soldering) and a sedimenter if you need them.

[Head Womble]

If it was getting in before the lift pump changing the filter would make no difference, this one of the things that puzzling me.

[Julian]

Aren't you talking about two different problems here?

1) Filter blocking
2) Air entrainment

I don't think the two have the same cause.

There's a bleed screw on top of the filter.  Have you tried cracking that while it's running?

[Head Womble]

Aren't you talking about two different problems here?

1) Filter blocking
2) Air entrainment

I don't think the two have the same cause.

There's a bleed screw on top of the filter.  Have you tried cracking that while it's running?

No, I haven't messed with the bleed screw, even when changing the filter I don't prefill it, just start the engine and give it some throttle until the revs rise and off I go.

[Jamesrl]

It's a LawnRoamer what else do you expect?

[Head Womble]

I expect to be able to cut the lawn with it.

[Julian]

Aren't you talking about two different problems here?

1) Filter blocking
2) Air entrainment

I don't think the two have the same cause.

There's a bleed screw on top of the filter.  Have you tried cracking that while it's running?

No, I haven't messed with the bleed screw, even when changing the filter I don't prefill it, just start the engine and give it some throttle until the revs rise and off I go.

Yes, I do the same thing but I do bleed air off the top of the filter once it's running.  If you do that and then check it a little later, it will be a good indication of air entrainment.

[Head Womble]

I'll give that a go at the weekend.

[knighty]

if there's a small air leak it might be ok wih a new filter in.... then once the filter starts to block (even slightly) there's a bit more restriction so it either sucks in more air, or the air that's in there makes more of a difference ?

[therecklessengineer]

There's also a strainer in the lift pump. Not all of them are removable depending on what brand you have fitted...

[greasemonkey]

I wouldn't discount a failing lift pump. I've been caught out like that more than once.
It'll look like it's working perfectly, but as soon as the pressure comes on, either wanting more fuel, or a slightly blocked filter, and it just hasn't quite got it.

[Head Womble]

if there's a small air leak it might be ok wih a new filter in.... then once the filter starts to block (even slightly) there's a bit more restriction so it either sucks in more air, or the air that's in there makes more of a difference ?

This is my thoughts,
When a new filter is fitted is back to full power, it then drops off slowly until that critical point when it tails off very quickly.
It's not my fuel as the wife's car doesn't suffer at all.

[Head Womble]

There's also a strainer in the lift pump. Not all of them are removable depending on what brand you have fitted...

It has a Delphe lift pump, the one with the filter and I checked it a few weeks ago, all was clean.

[Head Womble]

I wouldn't discount a failing lift pump. I've been caught out like that more than once.
It'll look like it's working perfectly, but as soon as the pressure comes on, either wanting more fuel, or a slightly blocked filter, and it just hasn't quite got it.

I replaced the lift pump a while back, it was doing this before and since.