strange power loss 1/2 full tank

[jaky cakes]

Hiya folks - i've got a wierd problem i'd like to run by you all for some input.

My truck has developed a problem with fueling when level gets below 1/2 full.
I'm running on 66%WVO dried and filtered to 1ym - which I've used for 3 years or so without concerns.
regularily serviced - fuel filter changed recently and often run redex / ATF fulid through once a month.

The problem is this - once level gets below 1/2 full - engine sounds rough at idle as if running on 3 cylinders and upon pulling away she hesitates and looses power intermintantly throughout reving. engine check light comes on and plumes of whiteish/grey smoke out of rear.

When this happens the fuel filter prime button gets sucked/jammed down, and the fuel lines are empty both to and from filter housing. I fitted clear fuel lines in engine bay last year - that's how I know they're empty.

If I remove filler cap there is no hissing / sucking as such.

I've cleaned the wee breather non return valve on tank.

Once tank is refilled to top - the problem disappears until the level gets down again.

So I'm thinking there must be something cutting off supply at tank end of fuel supply, as opposed to blocked fuel filter - as vacuum is drawn on whole line - not just on filter to engine line.

Is there some kind of filter type thing inside tank - or is there a lining on inside of tank that could be coming away on blocking outlet??

Really got me confused this one!! - how much chew is it to remove the tank? or can the fuel line be accessed with tank in situ??

Ohh and what is the best way to empty tank?? ( apart from driving it like you stole it!!)

any help/ input greatly appreciated.
Cheers

[That Ruddy Squirrel]

Isn't there a filter at the tank end as well - perhaps that's blocked


Trev

[BUSHWHACKER]

There's a small breather valve on top of the tank clipped to the tank edge. Pull it off and make sure it and the rubber pipe is clear.
p.s. My 2.4 tank, I guess the 3.0 is similar.

There's a drain plug/bolt at the bottom of the tank that can be removed without taking off the tank protector plate.

[jaky cakes]

Isn't there a filter at the tank end as well - perhaps that's blocked


Trev

That's what I'm thinking as well but unsure if there is one

There's a small breather valve on top of the tank clipped to the tank edge. Pull it off and make sure it and the rubber pipe is clear.

I blew them out a few weeks back when problem first occurred..

It only happens ( maybe coincidence) when tank gets below 1/2 full. Happened last 4 tank fulls.

Now this may sound a bit daft, but it's as though tank oultlet pipe is getting blocked by something once level gets low.

[GRASSMAN]

Hi mate,
The fuel pick up pipe in the tank may perforated near the
half way mark, allowing air to be drawn into the fuel line and
causing this problem.
Hope this helps.

Gman

[jaky cakes]

Hi mate,
The fuel pick up pipe in the tank may perforated near the
half way mark, allowing air to be drawn into the fuel line and
causing this problem.
Hope this helps.

Gman

Thanks for that Steve...
my problem appears to be a blockage - hence tha vacuum in the fuel line as opposed to drawing air - but may well be associated!!

I seem to have checked everything bar the tank itself.
I guess I'm gonna have to bite the bullet and take of tank to make sure..but how much of a job is it to remove??

[BUSHWHACKER]

There's a small filter on the back of the fuel pump on the 3.0, although the problem would be there regardless of how much fuel was in the tank.

Dropping the tank isn't difficult, just time consuming.
Remove filler cap.
Drain tank via the drain bolt underneath.
Remove tank protector.
Loosen clamps on the filler hose and in/outlet pipes.
Remove bolts and lower tank.

Much easier to get at the hose clamp on the filler tube if you have a bodylift.

While the tank is off, clean/hammerite it and the chassis behind it also check the hard brake lines as wet mud gets trapped behind there and corrodes the lines.

[GRASSMAN]

Thanks for that Steve...
my problem appears to be a blockage - hence tha vacuum in the fuel line as opposed to drawing air - but may well be associated!!

I seem to have checked everything bar the tank itself.
I guess I'm gonna have to bite the bullet and take of tank to make sure..but how much of a job is it to remove??

Just got out from under mine, looks like tank guard first, then
under n/s wheel arch, and remove panel, (a few bolts) to expose
filler pipe fittings, dissconnect fuel pipes, (rubber to steel) and lower
tank on a trolley jack, take care with the electrics, (dissconnect
the batteries?) there is a drain plug towards the rear of tank
6 gallons of fuel will be quite heavy, so take care.

Gman

[Bogus]

What makes you sure your tank is half full. Im assuming thats because 30 litres or so makes it full again ?
I know this sounds terribly obvious and likely to offend, but is there a chance that when you think its half full its nearer empty?

Is there a chance that over the last three years you have collected a layer of something ( fats , whatever) with a lower SG that is floating on top of your fuel and when you get to half way this layer of stuff causes a blockage?

I think my first move would be to drain the tank and see what comes out,

Bogus

[jaky cakes]

There's a small filter on the back of the fuel pump on the 3.0, although the problem would be there regardless of how much fuel was in the tank.

Dropping the tank isn't difficult, just time consuming.
Remove filler cap.
Drain tank via the drain bolt underneath.
Remove tank protector.
Loosen clamps on the filler hose and in/outlet pipes.
Remove bolts and lower tank.

Much easier to get at the hose clamp on the filler tube if you have a bodylift.

While the tank is off, clean/hammerite it and the chassis behind it also check the hard brake lines as wet mud gets trapped behind there and corrodes the lines.

Just got out from under mine, looks like tank guard first, then
under n/s wheel arch, and remove panel, (a few bolts) to expose
filler pipe fittings, dissconnect fuel pipes, (rubber to steel) and lower
tank on a trolley jack, take care with the electrics, (dissconnect
the batteries?) there is a drain plug towards the rear of tank
6 gallons of fuel will be quite heavy, so take care.

Gman

Thanks for your help guys - much appreciated.
Going to try to syphon most of tank by mouth then remove dregs via drain plug. wish me luck!!
will write up findings!
cheers

[jaky cakes]

What makes you sure your tank is half full. Im assuming thats because 30 litres or so makes it full again ?
I know this sounds terribly obvious and likely to offend, but is there a chance that when you think its half full its nearer empty?

I'm going off distance travelled rather than the gauge - i know I get around 400kms per tank.

Is there a chance that over the last three years you have collected a layer of something ( fats , whatever) with a lower SG that is floating on top of your fuel and when you get to half way this layer of stuff causes a blockage?

I think my first move would be to drain the tank and see what comes out,

Bogus

That is my thoughts - I've seen somefuel monsters in tanks over the years - grey jelly growths in oils/ fuels.

going to start draining tonight then possibly tank off tomorrow.

cheers

[jaky cakes]

just finished syphoning / draining tank. 20 litres via syphoning and then dropped drain plug for remaining 10 litres or so.
In the drained 10 litres, i've found a couple of hard tar like lumps about 5-6mm in diameter which crumble between thumb and finger. also found (more alarmingly) a hard metalic lump (too hard to file and ever so slightly attracted to a magnet - ie ferrous).
At first I thought these lump may have part of injection pump - being so hard - but then realised this lump (about 1/2" diameter) would not have able to pass through return line to tank. I don't think this material is used within the tank so presume it must be part if the filling station pump that has been transfered to my tank when filling.

So anyway it seems my tank may have a considerable amount of lumps of the tar like substance - a few of which fell out of the drain hole. So tomorrow I'm taking the tank off for a flush and thorough clean.

[GRASSMAN]

Hiya Jakey,

Just a thought.
These tar like pieces? could they be rubber? ie the insides
of your fuel lines, they can only be from the return pipes tho'
as feed pipe probs will be stopped by the filter. Have you got
any "crunchie" fuel pipes?

Gman

[johnd]

hi mate dont know if you have sortred it yet but i have had a few cars in this year with the same thing.
i have never been in a surf tank ( yet ) so am not sure.

but all the ones that i have done have had an o ring seal on the pickup pipe in the tank , so as the fuel drops below the seal it will suck air .

this could also be a split in a pickup pipe doing the same thing .

anyway good luck

john

[jaky cakes]

well all done and back on and running.
took the tank off and removed all attached plates/covers (sender unit,fill pipe etc) and looked inside. found a layer of what looked like thousands of waxy flakes. the tank sides were coated in a white slimey waxy coating. the screen on the end of the fuel outlet pipe was choked in a similar wax.
so filled tank with 1 gallon of diesel and scrubbed the inside walls with a long bottle brush. emptied and refilled with more deisel to rinse. Now spotless inside. I took the opportunity to under seal all the missed areas behind tank, as well as tank itself and refited. filled tank half full of deisel and bleed fuel through to filter and went for a run - OK.
can only presume the waxy flakes are from a while back when i was using SVO from makro, once or twice i noticed the cartons having a white waxy layer at bottom - presumable a harder fat that I thought would melt or desolve with the diesel.
So all done - all in 6 hours work and a bugger of a job by yourself espescially trying to manovre tank and feed filler hose back into place.