Intank Fuel Pump Question

[michael bentley]

I bought a 2002 75 diesel auto 2 months ago. I have been told that I should
not let the fuel go down below a quarter full because the fuel pump may not
work below this level, and the engine would then cut out. very inconvenient.
especially on the motorway and reduces the range between fill up to about
250 miles.
before i found this out i let the fuel go down well below this and had no
problems. nothing in the handbook about this. Is someone winding me up
about this?

[klarzy]

Originally Posted by michael bentley

I bought a 2002 75 diesel auto 2 months ago. I have been told that I should
not let the fuel go down below a quarter full because the fuel pump may not
work below this level, and the engine would then cut out. very inconvenient.
especially on the motorway and reduces the range between fill up to about
250 miles.
before i found this out i let the fuel go down well below this and had no
problems. nothing in the handbook about this. Is someone winding me up
about this?

Hi and welcome...

it can be an issue on some models if the in tank pump (ITP) is a little tired or non operational... if both the ITP (If present (eliminated on newer models)) & the UBP (Under bonnet pump) are ok then you should have no problem..

If you do a search on the forum for those terms then there is a lot of information

[Ken Lion]

It's not a wind up, just a sensible precaution.
There is a fuel pump in the tank and another under the bonnet.
If the tank pump is failing the under bonnet pump can still cope with the task so long as there is 1/4 tank of fuel.

edit: sorry Klarzy, didn't see your post.

[Rick-sta]

In tank fuel pump failure is quite common on our diesels, and if it isn't working, then yes the engine will cut out if you go lower than a quarter tank of fuel. Although I managed to get to the last 1/8th of a tank before mine cut out on me.

Best way to check turn the key into position 2 (i.e the one just before starting the car) and then pop the fuel cap off and listen for a humming noise coming from the rear fuel tank. If there is a humming noise then the fuel pump is working, if there's silence then it's most probably not working.

Rick

[Rick-sta]

damn it too slow!

[Mike Noc]

Originally Posted by klarzy

Hi and welcome...

it can be an issue on some models if the in tank pump (ITP) is a little tired or non operational... if both the ITP (If present (eliminated on newer models)) & the UBP (Under bonnet pump) are ok then you should have no problem..

If you do a search on the forum for those terms then there is a lot of information

Pete ITP's don't tend to get tired they just pack up. The commutators wear down to nothing.

It was the UBP that was deleted on the later cars and an uprated ITP fitted.

Sounds like the OP's ITP has indeed packed up. As mentioned check to hear it running. With the system running as it should you can run the tank down to the light coming on every time if you want.

[mh007]

According to the OP, he has let the level drop well below 1/4 tank which would suggest that the in-tank pump is still working perhaps ?
There is a venting system in the tank so when the in-tank pump is working fine, it can still pump fuel to the under-bonnet pump when the tank is virtually empty however, when the in-tank pump fails & the fuel level drops below 1/4 tank, the under-bonnet pump struggles to pull any fuel from the tank & therefore, you end up with a non-runner.
As already said, you can do a simple test to see if the in-tank pump is working:
Ideally have someone turn the ignition on while you either place your ear to the fuel filler neck (cap removed) or by the O/S rear seat.
If you hear a humming/buzzing noise for a period of time, the in-tank pump is pumping, no noise, it's not.
You can just replace the actual pump without the need of replacing the whole assembly/sender unit.
It's also worth saying that if the in-tank pump has failed, you may find the under-bonnet pump is tired as it would have been working overtime.
Both pumps are not expensive to buy.

[Mike Noc]

It depends on whether he was driving on a motorway or winding roads. Fuel sloshes over the saddle on winding roads and you may go well below a quarter of a tank and get away with it.

It is when the level on the offside saddle drops to the top of ITP that the engine stops. There is a priming valve built into the top of the pump and once this is uncovered air gets drawn in by the UBP and its game over.

[Rick-sta]

I was driving on the motorway and got to 1/8th of a tank with the low fuel light on before mine cut out. It actually had me thinking the in-tank pump was working.

[klarzy]

Originally Posted by Rick-sta

I was driving on the motorway and got to 1/8th of a tank with the low fuel light on before mine cut out. It actually had me thinking the in-tank pump was working.

I have gone far lower with no issue, drove for 40 miles with the light on and the needle pointing south before I turned chicken...