hmmm, ok. any idea how that could happen when I have replaced the sensor already and the wiring seems to be ok?

I removed the pump unit from the tank and didn't really learn a lot, the pump is all contained inside a plastic housing thing and i couldn't see a way of taking it apart. I saw people talking about a strainer getting blocked on other threads but on mine I cant see how id be able to check it, if it even has a strainer that id be able to clean or replace.

Johnson4130 said:

hmmm, ok. any idea how that could happen when I have replaced the sensor already and the wiring seems to be ok?

I removed the pump unit from the tank and didn't really learn a lot, the pump is all contained inside a plastic housing thing and i couldn't see a way of taking it apart. I saw people talking about a strainer getting blocked on other threads but on mine I cant see how id be able to check it, if it even has a strainer that id be able to clean or replace.

Click to expand...

Not specifically.. no

Unplug the sensor.. check for 12v at pump

Bridge sensor wires.. " - " -- ""

varesecrazy said:

Your rail pressure sensor is back in the frame..

If it says its 'full' pump demand is off

Click to expand...

oh just thought, if i managed to get a good scan tool on it it would probably show up on there is this was happening. ill try again to get one working.

varesecrazy said:

Not specifically.. no

Unplug the sensor.. check for 12v at pump

Bridge sensor wires.. " - " -- ""

Click to expand...

i cant get a read on the pump whilst it is plugged in, if that was going to work though the pump should just run so ill try that. will have to be tomorrow now though i don't fancy working in the dark

Thinking out loud..

Remove sensor.. so rail is at atmospheric pressure

Disconnect blue fuel hose.. place in a pot

When you turn ignition.. how long does pump run : how much fuel is delivered ?

Hi all,

The diesel fuel rail is pressurised by the high pressure diesel pump. This only happens when the engine is rotating, either by the starter motor or when engine running.

The high pressure pump is supplied diesel by the in tank lift pump.

Cheers Jack

My 1.3's run the tank pump for 10+ seconds

Something is obviously not quite right here

Going back to the start of this thread it looks like someone said there is a problem with the fuel rail pressure sensor-perhaps the problem is there is no pressure building in the fuel rail.
No pressure or insufficient pressure in fuel rail means no start.

It has been suggested already to check fuel rail pressure while starter motor turning engine-excellent suggestion.

jackwhoo said:

Going back to the start of this thread it looks like someone said there is a problem with the fuel rail pressure sensor-perhaps the problem is there is no pressure building in the fuel rail.
No pressure or insufficient pressure in fuel rail means no start.

It has been suggested already to check fuel rail pressure while starter motor turning engine-excellent suggestion.

Click to expand...

Yes i checked the pressure at the rail, there was none. i cant say for definite the high pressure pump is working but i strongly suspect that that is not the issue and the lift pump not working is my problem. I already drained a lot of the fuel out of the rail by changing the sensor and undoing one of the pipes to the injectors, therefore if the lift pump is not providing any more fuel (which if definitely isn't) then the high pressure pump will never be able to make any pressure as it has no fuel to work with.

I just need to figure out why my lift pump only blips on for a fraction of a second and then cuts out. I know it works as it runs when given an independent supply, i know there is some kind of power to it as it blips on and pumps a tiny amount of fuel out when the ignition is turned on, i just don't know why it cuts straight of again.
I went back to the pics of a fuel pump on another thread and i now think i know how to take it apart and check the strainer so i'm going to try that tomorrow and some of other the other things suggested here.
Would welcome any more ideas.
Cheers
James

The pump in tank will turn off when up to pressure, maybe pressure sensor is not working.
I would suggest doing live read to see which sensor is saying what.

Is there another sensor for the low pressure side then? i wondered if that was the case, though if it is then why do they always run for about 10s normally?

managed to partially dismantle the fuel pump assembly so i could see the strainer today, whilst i didn't actually clean it it looked totally fine so im confident that is not the issue. I also swapped the fuel filter as I had one waiting to be installed and there is some kind of sensor on the bottom so i wondered if that was anything to do with it but still no joy. I also unplugged the fuel rail sensor and it blips the pump exactly the same as if the sensor is plugged in. not sure where else to look now.

I have found something, its definitely an electrical fault and nothing wrong with the pump.
I found the relay for the fuel pump by pulling them 1 by 1 and trying the ignition to see which one stopped the fuel pump from bumping.
I then tested for voltage at the coil terminal for the relay (with the relay removed) and there was only 8v which explains why the relay is briefly closing causing the pump to bump but it cant hold on. now just to figure out why ive only got 8v

Done some more testing and learnt a bit more, i think the relay i have been looking at is actually the fuel cut off relay. The car has now started showing a message "fuel cut off unavailable" on the dash when you turn it on which is new. I traced the wire which provides coil voltage from the relay box back to the ecu (a white wire with a green stripe) and did a continuity check which showed the wire was all good at 0.3 ohms. However after searching the forums for "fuel cut off unavailable" there were several people talking about damage to the wiring where it goes into the boot hatch. I had recently repaired some damaged wires in there which had been stopping the boot latch from operating so i stripped all the covers back again and discovered the are two white with green stripe wires in that part of the loom but neither has visible damage, I have also spotted there is one in the drivers footwell the same colour.

Basically I'm thinking this white and green wire must run all over the van as part of the fuel cut off circuit and it is damaged somewhere which is causing voltdrop at the relay and cutting off the fuel supply. question is how do i find the break? do i need to just rip the whole van to bits and find every run of wire in that colour? there must be a better way?
additionally the van now unlocks itself again when I lock it unless I disconnect the battery, which is fun.
I also have a reading in k ohms when i measure from the fuel pump relays coil live terminal to the battery negative. I think there should be no connection there and this is due to a broken wire shorting slightly to earth somewhere, causing the voltdrop i have found. Other relays i tested didnt have any connection to batt negative when i tested the same way but this might be a red herring as i have found weird k ohms range connections on stuff before that have turned out to be nothing.

I ended up taking this to a diesel specialist who sorted it out for me.
The volt drop i found on the pump relay was a red herring that was somehow being caused by the real problem. They found that one of the wires going to the high pressure fuel sensor was partially broken. This meant that when i tested it for continuity it measured ok but when the ecu was trying to read a signal down it it was getting a false reading. there was also a bad connection on the plug into the ecu, they had to fit a new pin to the plug and ecu to get it to make contact properly.

Glad you got to the bottom of it..
Thanks for updating