I'll give that a try mate, will try and get some some new bolts and nuts and see how it goes.
Cheers for the help.
Cheers for the help.
jamesmartin
Well-Known Member
you have 2 pumps in the tank unit,fuel goes from lp pump to filter then back to hp pump then to engine ,returning to the filter head rather than to tank ensures fuel doesnt drain back overnight
jamesmartin
Well-Known Member
stick to m6 use a recoil kit if you can ensure top is full located before tightening nuts,its trying to pull top down that shears the threads
sierrafery
Well-Known Member
It's only one pump with two compartments James... and in a setup like the OP thought first time that only the return from engine and LP return to pump are connected most of the fuel passes above the filter not through it hence the LP feed is on the other side and my statement that it's not filtered
jamesmartin
Well-Known Member
if you look at the filter head you will see the 4 ports either enter the space above the filter or center threaded tube, 2 outer most do top space 2 inner most center tube,of front ports one does top the other center tube so fuel has to pass through the filter as with op only 2 pipe setup as he mistakenly thought
with the pump, theres a plastic vane impeller pump at the bottom takes fuel from swirl pot, then out through hose to filter, back via hose to steel hp gear positive displacement pump out through green hose to engine
sierrafery
Well-Known Member
I dont want to contradict you just to understand your theory... so if there are two pumps means that if you remove the metal pump the other impeller pump should still work? that impeller pump is driven by what? as it's only one electrical feed which is connected to that one pump which IMO is a two stage LP/HP pump hence if the HP stage fails it's still running on LP with lower currect draw... i'm opened to other explanations though
Last edited:
jamesmartin
Well-Known Member
one motor one shaft both pumps are driven by the same motor and shaft sat on top of pumps unit, lp pump on bottom with filter screen attached(separate to the outer screen on the swirl pot housing), then a chamber then hp pump, fuel enters through screen into lp pump then out through lp feed to filter no7 in diagram then back by no6 to the chamber to feed hp pump, then out to engine by no8
sierrafery
Well-Known Member
OK i understand how it works, it seems it's just a matter of semantics as in my head i can't consider two pumps as long as it's one motor... maybe that's why LR also named it ''two stage pump" 
AHA!
That now makes more sense.
This is what happens when you never have to take part of a vehicle apart. You don't get to know and understand exactly how it works.
I think this is why it is possible to buy an entire Haynes manual on the Weber carb.
Emulsion tubes etc, this used to befuddle peeps in the past yet I understood it and could work with it, but only because I had learned how to, through necessity as well as interest.
TBH, airflow, exhaust, cams, valves, old skool fuel systems, filtration, profiles of trumpets or whatever you want to call the bits you stick on carbs to improve flow, all of these I studied, how to make various cuts on the backs of valves and their seats. And mostly how to sort out the truth from the rubbish.
I have even written articles on springing and stuff for kit car magazines. But as any teacher will tell you, you have to want to learn it before you learn it. Which is why I really do have a bit of a mental block when it comes to modern car electronics.
As for the fuel system on the TD5, I was about to go back to the diagram to see if I could get my head round the necessity for the double filtration, but then I saw your post. And the thing about fuel not draining back makes perfect sense. Except me being me, I cannot see why a simple one way valve could not do the same job.
Thanks so much for all this and I will be messaging you later on with something I think your son might find useful to help him a bit with his learning, if that is OK with you.
replied to the first post before realising so much more had been posted on this. Seems i'm not the only one confused by it all.Yet if we each had one on the bench and took it apart, we'd grasp it immediately.
Another example, despite having rebuilt gearboxes, I only realised the other day that synchro rings only ease the gears togther and then move away. I imagined they stayed agains the gear until next needed, i.e. until the lever disengaged one to move towards another set. Seems mad but then unless you have a plexiglass top and can see it all happening when driving it isn't obvious. Well to me it wasn't! And with the plexiglass top it would be continuously awash with oil so that was a stupid idea right there!
jamesmartin
Well-Known Member
im not certain why the system is like it is can only think its so the steel hp pump which isnt very hp really, gets fed with filtered fuel
I think that makes sense. If the hp pump gets worn by the bits of sh!t that can get into fuel, espcially things metallic then a/ the pump would wear and not be even as hp as it supposed to be and b/ it would shove the metallic etc bits up towards all ther injection gubbins and we all know what can happen then.
Also don't you think water might be a big issue? I have heard that water is a big no no in injectors and of course can eventually rust metal bits like, maybe in the pump.
I once had water ingress into a kit car fuel tank. It took me ages to work this out as I could only see the carburettored fuel system as having a fault. The car ran but it seems to need to run on full or partial choke the whole time, and it played merry harry with fuel consumption. In the end I fitted a diesel fuel separator and that sorted it, and enabled me to see the problem. Getting the water out of the tank was no problem and things seemed to be fine after that.
Until I noticed fuel leaking out of the tank. The tank was a steel tank with special fire resistant stuff in it like wire wool. (It took ages to fill cos of it.)
So the water had been accumulating in there for some time right up until the point where the pick up pipe actually started picking it up.
So, new specially made fuel tank time, made for me by a guy recommended to me who actually rana LR garage. He turned out to be a real cowboy and the tank came with the mounts on the bottom instead of the top. The guy told me my drawing was rubbish until I pointed out, on the mounts I had actually written "top". It was underslung, not fitted to the floor of a boot.
So I had to take it on, grind the mounts off, fab new ones and then lie under the car, in the dark, in a puddle marking up the points to drill them, then take it back off, drill them and then refitting the whole thing. As it was February and I was leading a convoy of cars with it the following day!
Lesson learned: do not use a pressure washer near a Monza style fuel cap! (Or probably any type of fuel cap, but then most are behind a flap, innit!)
jamesmartin
Well-Known Member
waters allways been an issue old lift pumps had waterproof gauzes, td5 has a drain or switch on the filter
NPG
Well-Known Member
I'm pretty sure that the low pressure feed is designed to improve the performance of particle filtration and water separation in the diesel filter. Also, when fluid is passing through the filter membrane, it is restricted and too much pressure could result in turbulence and bubbles to form due to recirculation cavitation, which could easily damage the pump. The pump unit is effectively 2 pumps in series, rotating at constant speed and designed to deliver fuel at sufficient enough pressure (4 bar) to sustain a constant flow, reduce pulses caused by the injectors and also minimise the time any given volume of diesel stays in the engine long enough to absorb too much heat. At least, that's what I think and I have to say that, in my limited experience of diesel engines, whoever designed this fuel delivery system deserves a medal for its reliability and sheer simplicity.
jamesmartin
Well-Known Member
NPG
Well-Known Member
Maybe you're right and I should not make judgments based on my own experience. But I only ever had to replace a leaking regulator and a fuel pump - not even the injector washers and seals although I did buy a set years ago just in case ! And mine is 21 years old with 330K kms on the clock.
jamesmartin
Well-Known Member
sierrafery
Well-Known Member
I changed my pump two years ago when the vehicle was 18 years old and had around 180K miles but the pump was running well just the sender failed so as i had a new one for spare i fitted that one. IMO they live longer if the tank is kept above quarter all the time cos the hot return fuel is mixing with more cold fuel in the tank and the pump is not exposed to so much heat.
Good advice in any fuel system to try to run with at least a 1/4 of a tank, helps to avoid picking up sh!t.
Have drained the filters on both TD5 and 300tdi lots of times, never seem to find water in them, yet ages ago, when turbo diesels started being fitted to smaller cars, in our case a Renault 19, I regulalry found water. Do you think this could be because so many cars are diesels now and the tanks on forecourts get filled and emptied so much faster?
sierrafery
Well-Known Member
Sorry, i have no ideea about what is the real cause for water ... what i know is that all my friends who had more than one pump failure in 15 years saw the low fuel warning too often anf filled small amounts of diesel each time while i've seen it maybe twice in 20 years but i usually fill it up to the top and dont let it much below quarter
....it even runs better with cold fuel
