Thread: Long range tanks and fuel pumps

i did notice on george 130's truck that his was making a nasty noise aswell and his is a long range tank.

also on this topic about hard to get to... i remember seeing a post either here or elsewhere with someone who basically cut an access hole into the floor of the fender

that too would be me, I havent cut mine yet but once the workshops back on the ground its happening, pics will follow.

Mate, thanks for the detailed run-down - this is very helpful.

So what do you reckon - should I be getting that much noise with 20L still in the tank? If I rule out heat (not a factor) it would appear I'm suffering the cavitation factor predominately.

I accept the echo chamber theory too, but the fact that I'm noticing a performance impact is telling. Do I get the vendor to take off the tank and check for the placement of the fuel pickup?

Originally Posted by Blknight.aus

heres the rough as guts skinny on the setup, the terms aint exactly what they should be but close enough that you should get the idea

While getting a tank modified, I was talking to the person who runs the workshop that manufacture the Longranger tanks.

From what I recall, he mentioned that with rover diesels, they found that they had to put the return line into the baffled section where the fuel pick-up is located.

AFAIK most tanks have the return line some distance from the pick-up to keep heated fuel and turbulence away from the pick-up.

I didn't make a connection at the time, but his comment may have been in regard to the Td5 fuel pump issues.

Do you know whether your fuel return line discharges into the pick-up section of LRA tanks?

Is there a way to swap to an external pump?

Originally Posted by Bush65

While getting a tank modified, I was talking to the person who runs the workshop that manufacture the Longranger tanks.

From what I recall, he mentioned that with rover diesels, they found that they had to put the return line into the baffled section where the fuel pick-up is located.

AFAIK most tanks have the return line some distance from the pick-up to keep heated fuel and turbulence away from the pick-up.

I didn't make a connection at the time, but his comment may have been in regard to the Td5 fuel pump issues.

Do you know whether your fuel return line discharges into the pick-up section of LRA tanks?

No idea - but will certainly bear in mind...

Originally Posted by Blknight.aus

heres the rough as guts skinny on the setup, the terms aint exactly what they should be but close enough that you should get the idea

****backround info

all diesels have a low pressure and a high pressure fuel system...

common rail(also known as unit injectors, electronic injected or hydraulic electrically actuated fuel injected (HEUI-hydraulic electric unit injectors) engines have 3

a low pressure a medium pressure and finally each injector has its own high pressure section...

ok normal mech diesels are pretty simple a low pressure pump with a good flow volume pumps fuel around fills the injector pump plunger as needed (thats the bit that gets you your timed high pressure injection pulse) and excess is used to lubricate the injector pump (regardless of type) and cool the thing.

the fuel system typically follows this kind of scematic

sedimentor/strainer-lift pump-filter-fuel injection pump-return to tank.

with unit style injectors you can have up to 3 pressure levels, for simplicitys sake i will only describe the workings of the td5 setup if anyone wants to know the others I'll go into them too.

the fuel system works as follows..

strainer-lp pump-filter-mp pump-mp fuel lines-unit injector-return line.

with any form of unit injection the plunger that creates the HP fuel pulse that fires the injector is built into the injector itself there is no high pressure fuel lines as such (injector lines) as its all in one piece the plunger moves the same amount every time and as per typical fuel injection the spill port drops the pressure off when the required injection is done.

the td5s plunger is mechanically driven and the spill port is controled by electronics which is why the oil in the harnes problem is such a big one, if the volts reaching the injectors isnt right the injection just doesnt happen.

***the bit on the fuel pumps in a td5

The fuel pump is pretty simple...the low pressure high volume part of the pump grabs fuel out of the tank through the strainer, pumps it to the pickup side of the medium pressure pump via the filter. The medium pressure pump doesnt shift as much fuel so excess bleeds of into the cup that both pumps sit in to cool them. From there the filtered medium pressure fuel is sent to the injectors to fill them prior to injection and cool them down.

The fuel pressure regulator keeps the pressure to the supply chamber at the correct level to ensure that the injector plunger chamber is correctly filled. As fuel demand drops so does the fuel manifolds pressure.


your problems begin when a, the fuel is getting hot enough to no longer cool the pumps effeciently. b, the low pressure pump begins to cavitate.

point a isnt so bad.... youd like to avoid it if you can but you cant always...(if your car is parked on an 80 degree road surface with say 1/4 of a tank and theres no wind your going to have hot fuel)

part b is the problem when the pump begins to cavitate its got air in the line not much but enough, when the air hits the medium pressure pump most of it if not all is spat out via the relief valve so you still get good fuel going to the injectors. But the pump must now work harder to deliver the required fuel to the injectors and as its a fixed displacement pump it must spin faster to do so. When you get really low on fuel the pump will be screaming its nipples off as it no longer can keep the pressure up to the fuel manifold on the engine..

The engine will still run as the fuel pressure regulator will be doing its best to stop fuel from returning to the tank and so long as there is some fuel in the plunger chamber the injector will fire, just not as much.

(when this happens you will notice a loss of power, if you lift of and drive slower as the fuel demand is less you need to inject less so you will get power again up to the point where your injecting more than the lift pumps can deliver)

so when you run your fuel level low your attacking your pump from 3 directions...

1. your not cooling it, thats bad
2. your making it spin faster, thats also bad but the worst is
3. your not lubricating it, the diesel is the lubricant, if its areated its not lubing correctly.

On a note of lesser evil....

you will notice the fuel pump noise more when the tank has less fuel in it, the tanks a big resonance chamber when its empty... bang the side of an empty 44 gallon drum then a full one, you'll get the idea..


Hope thats insightful or helpful to yall.

Dave, I would just like to thank you for the reams of extremely useful information you post here, well done it is most appreciated, Regards frank.