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paulob1

fuel sup[ply problem...just check this out for a queer one

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okay on the leyland daf, when the fuel reaches a certain point in the tank the truck refuses to run...

 

we started at the tank and the fuel pick up shows that it has never been left dry at one point, it is bright shiny coated, the rest of the pipe is time faded...

 

so my thoughts are that the lift pump cant actually lift the fuel out of the tank once it gets so low. Now that would be silly.

 

So we get a jerry can put the can on top of the tank and brum away she goes, no more problems running sweet as normal.

 

so my thoughts are that there must be a tiny air leak in the system, such that when the tank is full or above the specific point it works fine the fuel running freely enough to make the air leak unnoticeable...but once below or at this point the fuel draw is so great that the air leak becomes too intense and she then sucks air rather than diesel...

 

now we will strip the system down and hopefully find the source of the leak...there are only a handful of joints and they cannot be difficult to clean and secure but I know when i bought it Dave was having the devils only job keeping it running, he woreked on all the pipes and it seemed to work fine, but now its playing up again, so trip and refit is the next step...

 

Anyone got any other ideas...there are no holes in the pick up pipe at the specific fuel level...it is sucking air, but we have yet to ascertain from where...any ideas on how...we will change both the pre and post pump filters in the mean time...anyone know where I can get them from...assume a normal truck dealer would do them...

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Paul can actually look inside the fuel tank? Father-in-law once had an intermittent running problem in his car that for quite a while defied all tests & explorations. The cause was a rag floating around in the fuel tank that at certain levels & speeds got sucked over the fuel uptake pipe.

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had a look insid with fibre optic scope, cant see anything other than diesel but think we may empty the old girls tank and take it off if we cant find the fault, it has to be a very very small air leak somewhere but where...there are not that many joints to check..but there is certainly something going on with the depth of the fuel in the tank, i would guess that this tank has never dropped below 20 gallons of fuel, ever....

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Had a Bedford MK or MJ come in to Workshops, broken down on the road and recovered, driver said it had a history of fuel problems, since the tank was repaired. I took the tank off and had a look inside.......guess what, it was a delivery note from Serck, floating around inside. Some numpty had rolled it up in the neck I guess.

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I worked at one place and we had Massey Ferguson come down to demonstrate the new latest greatest Dyna trac! The last word in modern tarctor design. With a great fanfare the demo driver swung into the yard with the shinest tractor I have ever seen. That promptly stopped dead and refused to play. Hours later, paint flakes found in a fuel line! Some prize**** had painted all the fuel lines bright gold before fitting. :nut:!

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I knew a Jaguar that ran fine until low on fuel.

 

Upon investigation the suction pipe was close to the bottom of the fuel tank.

With the full weight of fuel in the tank the bottom bowed slightly increasing the clearance and all was well, but with little fuel in the bottom sprang up and flattened out closing off the pipe.

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Could the pickup pipe in the tank have a hole in it.

When fuel drops below this point it would start sucking air from the empty part of the tank.

 

Mike

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Hi Paul, the engine filter is a perkins OD 19596, any truck spares company should be able to get one. The filter nearest the fuel tank is a sedimenter/ heater assy so no replaceable element here.

May be worth blanking the end of the fuel pickup and pressure testing the pipework, including the sedimenter. The fuel shut off valve is also at a mid tank level so include this in the tests. 15psi is the normal test pressure for this type of component, (but doesnt allways show a suction leak). Good luck.

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I knew a Jaguar that ran fine until low on fuel.

 

Upon investigation the suction pipe was close to the bottom of the fuel tank.

With the full weight of fuel in the tank the bottom bowed slightly increasing the clearance and all was well, but with little fuel in the bottom sprang up and flattened out closing off the pipe.

 

i recon you might have hit the nail on the head Mike. You know the best way to check the pick up pipe for a leak is to blank one end with your finger bung the other nice tasty end in your mouth, suck and stick your tongue over the pipe and wait to see if you lose vacume.

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thanks guys, will give it a go tomorrow, thanks for the part number will get that fom the shop tomorrow...it looks new but will try anything right now...

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Have you checked the tank breather? If it is blocked then with no air to enter and replace displaced fuel a vacuum develops. The pump may not work against the vacuum. I know of instances with prolong fuel problems that were cured with a simple clean of a breather hole.

Just another thing to try.

Doug:undecided:

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A friend of mine put a new seal around the fuel cap of his Bristol RE bus, this caused a vacuum after a while, might be worthwile to check that?

 

Also, another friend found a bit of solder floating around the diesel that got sucked onto the pick up pipe stopping the flow.

 

I found part of a broom handle in my Mercedes 608D minibus fuel tank, bus opperators used to dip the tank with a broom handle, can only assume a bit rotted and broke inside the tank!

 

Mark

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thanks all good ideas i think tank removal and clean out is on the cards no matter what, but its the fact that this truck has a clear mark on the pick up pipe that has never ever been corroded because it has always been covered in diesel. its really really odd. there is a clear perfect stop line, like someone designed it to be like that but clearly it isnt supposed to be.

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I hate these sort of faults... To rule out the tank try to replicate the height of fuel in the tank and the same amount of lift to get it over the top of the tank say using a jerry can and a long piece of hose try to get the height of fuel in the jerry can the same as in the original tank, so they are the same height and see if it will run, if this works you can reassemble to original tank and try it again and it should fail if so you have a problem in the tank.

 

Good luck

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I once had a Golf with the same problem/symptoms.

In the end it was that someone had put the fuel feed to the fuel pump onto the fuel return line into the tank and vice versa. The fuel return line drains into the tank from half way up whereas the feed obviously feeds from the bottom...

might be worth a look.

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found the problem, its the through chassis brass fitting, it looks like it was mullered from installation and has been over tightened ever since. It is a bugger as the local truck stop doest do the long ones anymore and so we are having a bit of a job finding a replacement..ho hum at least we have the fault found, it will soon be fixed.

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