in tank pump

[3disco]

Originally Posted by James.uk

Hi Ian, I seem to recall Jules saying much the same thing, in that the in tank pump only kept the tank fuel level, but didn't send much fuel to the under bonnet one..

Logically if you upped the power on the ITPump, with an "out" feed, you could do away with the lil under bonnet one....

My lil ZX only has one pump and manages very nicely innit...
...

Hi Bob,there seemed to be several threads in the past which said if the itp failed then the ubp would shortly follow so change as soon as possible,so as said before why would it in any way compromise the ubp if fuel kept to around a 1/4 tank or over and how have they deleted the ubp,what feeds the high pressure pump?ps/ there are scones and cream in the freezer if you are local at any time.

[James.uk]

Scones and cream... mmm, I remember well our last visit, we had a lovely time.. And your place is a great place to spend time at..

I was down there in May, stayed at the coach house Chideock, but had guests so was unable to visit you...

I will visit again just as soon as I can find an affordable place to stay that allow lil white dogs..

Oddly, the last three places we rented for Hols down there, have all been sold..

Ummm, ah yes the topic... I think three fuel pumps is two too many!!!
...

[3disco]

Originally Posted by 3disco

Hi Bob,there seemed to be several threads in the past which said if the itp failed then the ubp would shortly follow so change as soon as possible,so as said before why would it in any way compromise the ubp if fuel kept to around a 1/4 tank or over and how have they deleted the ubp,what feeds the high pressure pump?ps/ there are scones and cream in the freezer if you are local at any time.

Does nobody know the answer?

[Mike Noc]

The reason the later system works without the UBP is that the ITP is more powerful and they also changed the pipework to suit a single LP pump set up.

Originally Posted by 3disco

Can you explain how the pump does both jobs as I do not see a physical connection to the outlet?

Hang on 3disco I didn't say it does both jobs, just that it isn't solely used for tank equalisation.

After looking at my CDT and my daughter's Freelander TD4 I do think the diesel fuel system is a bit more sophisticated than most people give it credit for though.

There are also venturi pumps in the fuel tank to assist in equalising the levels either side of the saddle. Of course Freelanders don't have those.

To try and get a better understanding of how they work I've run both the ITP and UBP pumps on the bench.

Interestingly the UBP doesn't draw all its fuel through a failed ITP. There are two valves on top of the ITP, one that is a normally closed bypass valve to bleed off any excess pressure, and the other a normally open vent valve that closes when the pump pressurises. This enables the system to be self priming.

So, although the UBP pump can suck air, it may struggle to self prime if the fuel runs out, and the ITP ensures the system can self prime. Important for a luxury diesel - if you run out you don't want to be out there pumping a fuel bulb for all your worth.

When they replaced the original set up with a single LP pump I think it was placed in the fuel tank to make it easier to self prime in the event of running out of fuel.

The vent valve is also the reason why the engine stops around the quarter full mark with a failed ITP: As it is on the top of the pump, as soon as the fuel level drops below it, the UBP starts sucking air and the ECM shuts the engine down due to lack of pressure registered by the HP fuel pressure sensor in the fuel rail.

It is often stated that ITP failure causes the the UBP to fail prematurely. What I think actually happens is that the ITP fails, and the car runs fine on the UBP as long as the driver doesn't let the fuel drop too low in the tank. Then eventually the UBP fails which they will do even with a working ITP, and both pumps are found to be dead so the connection is made that one pump took the other out.

Yes the UBP has a bit more work to do running on its own, but I ran mine for 20k miles with a duff ITP and it was still going strong when I replaced both of them.

It is also often stated that fuel passes from the UBP to the HP pump and what isn't used returns along with any injector leakback to the fuel tank. Not from cold it doesn't.

If you trace the pipework it looks like, apart from a leak off for excess return pressure, the unused fuel stays in the circuit and goes round again to the UBP, with the losses being topped up by the ITP, if it is running. The fuel only starts to return to the tank once the temperature reaches 73 C, with the spill back then regulated to stabilise the temperature of the fuel.

It is also often stated that to preserve your ITP you shouldn't let the tank ever fall below a quarter full, and that is pure bunkum.

If you always top up before the tank drops to a quarter full then you won't know your ITP has failed........ until the UBP does.

PS Just realised how much I've rambled on. Sorry about that - shouldn't sit down with the laptop and a pint.

[3disco]

Originally Posted by Mike Noc

The reason the later system works without the UBP is that the ITP is more powerful and they also changed the pipework to suit a single LP pump set up.



Hang on 3disco I didn't say it does both jobs, just that it isn't solely used for tank equalisation.

After looking at my CDT and my daughter's Freelander TD4 I do think the diesel fuel system is a bit more sophisticated than most people give it credit for though.

There are also venturi pumps in the fuel tank to assist in equalising the levels either side of the saddle. Of course Freelanders don't have those.

To try and get a better understanding of how they work I've run both the ITP and UBP pumps on the bench.

Interestingly the UBP doesn't draw all its fuel through a failed ITP. There are two valves on top of the ITP, one that is a normally closed bypass valve to bleed off any excess pressure, and the other a normally open vent valve that closes when the pump pressurises. This enables the system to be self priming.

So, although the UBP pump can suck air, it may struggle to self prime if the fuel runs out, and the ITP ensures the system can self prime. Important for a luxury diesel - if you run out you don't want to be out there pumping a fuel bulb for all your worth.

When they replaced the original set up with a single LP pump I think it was placed in the fuel tank to make it easier to self prime in the event of running out of fuel.

The vent valve is also the reason why the engine stops around the quarter full mark with a failed ITP: As it is on the top of the pump, as soon as the fuel level drops below it, the UBP starts sucking air and the ECM shuts the engine down due to lack of pressure registered by the HP fuel pressure sensor in the fuel rail.

It is often stated that ITP failure causes the the UBP to fail prematurely. What I think actually happens is that the ITP fails, and the car runs fine on the UBP as long as the driver doesn't let the fuel drop too low in the tank. Then eventually the UBP fails which they will do even with a working ITP, and both pumps are found to be dead so the connection is made that one pump took the other out.

Yes the UBP has a bit more work to do running on its own, but I ran mine for 20k miles with a duff ITP and it was still going strong when I replaced both of them.

It is also often stated that fuel passes from the UBP to the HP pump and what isn't used returns along with any injector leakback to the fuel tank. Not from cold it doesn't.

If you trace the pipework it looks like, apart from a leak off for excess return pressure, the unused fuel stays in the circuit and goes round again to the UBP, with the losses being topped up by the ITP, if it is running. The fuel only starts to return to the tank once the temperature reaches 73 C, with the spill back then regulated to stabilise the temperature of the fuel.

It is also often stated that to preserve your ITP you shouldn't let the tank ever fall below a quarter full, and that is pure bunkum.

If you always top up before the tank drops to a quarter full then you won't know your ITP has failed........ until the UBP does.

PS Just realised how much I've rambled on. Sorry about that - shouldn't sit down with the laptop and a pint.

Hi Mike,many thanks for your post,I just cannot see as you have said in an above paragraph "with the losses being topped up by the intank pump" as I could see no physical connection with the intank pump to the fuel outlet on the tank, I just cannot get my head round it,I am not saying you are wrong but as said I cannot understand it.

[Moodster020]

A bit overly complex for a fuel tank ive always thought, why didnt rover keep it simple?
It seems to fail regular with the amount of people having to change the units on here...

[bobthethird]

Out of general interest has anyone had a UBP fail when the ITP is still working, or have people just changed the UBP without checking the other pump.
I am thinking more about garage repairs, it is easy to diagnose the UBP, change it, and just ignore the other one. This of course is just storing up trouble for the future, and giving out cries of "That new pump didn't last long."

[Mike Noc]

Originally Posted by 3disco

Hi Mike,many thanks for your post,I just cannot see as you have said in an above paragraph "with the losses being topped up by the intank pump" as I could see no physical connection with the intank pump to the fuel outlet on the tank, I just cannot get my head round it,I am not saying you are wrong but as said I cannot understand it.

You aren't getting the fuel burning heater supply hose mixed up with the outlet pipe to the UBP?

The return pipe and fuel burning heater supply pipe are both situated in the offside tank module top and the outlet pipe to the UBP is on the nearside module top.

If you unplug the UBP then disconnect the outlet pipe on the nearside tank module and stick a smaller pipe in the connection and the other end in a jar, with key to position 2 you should get fuel flowing out if the ITP is working.

[HarryM1BYT]

About a year or so ago, a member did an extremely detailed write up with detailed diagram explaining how the fuel system worked. They were not themselves entirely convinced they had got it completely correct, but for those who might be interested in how it works it is well worth studying - but be warned its operation is extremely complex.

The system involves a number of valves, two pumps, a venturi system, a cooler and temperature regulation system.

[HarryM1BYT]

Originally Posted by Moodster020

A bit overly complex for a fuel tank ive always thought, why didnt rover keep it simple?
It seems to fail regular with the amount of people having to change the units on here...

Complex it certainly is, but I don't think the system fails as frequently as you suggest. You only get the failures reported in a forum, never the pumps which just keep plodding along for years as mine has done.