Hi all,
My Van, a second gen Doblo cargo with the 1.6 TD engine, has some kind of issue with the fuel pressure sensor (the high pressure one on the end of the injector rail). The van was intermittently loosing power for a split second then coming back which got progressively more frequent until it started cutting out completely.
I went to a garage and got it code read, they said the code was showing an issue with the high pressure fuel pressure sensor, mentioned above, and that it would likely be either an issue with the wiring or the sensor itself broken. I managed to get the van home but it cut out completely and wouldn't restart just before I got back so I had to push it onto the drive.

I tested out the wiring with a multi meter and all seems to be well, between the plug for the sensor and the big connector on the bulkhead (the furthest point I can access and locate the wire without a wiring diagram) the wires measured all good for continuity. I then tested the wires into the plug with the ignition on, one wire (yellow) has 5V on it so I assume this is the power, another wire (black and purple) has a direct connection to the battery negative terminal (0.8 ohms) so I assume this is ground and the other wire (red and green) I assume is the signal from the sensor, this didn't show any voltage with the ignition on so I thought the sensor must be broken.
I have replaced the sensor at an eye watering cost of £130 but it still wont fire up
Obviously I lost a bit of fuel out of the rail when I changed the switch, I did turn the ignition on and wait 10 seconds then off and on again several times before I tried to actually turn it over thinking that would prime the rail but no joy? Is there anything else I need to do to prime the fuel rail or bleed it or anything? I'm at a loss and would really appreciate any help
Cheers
James.

Are you SURE its actually getting the rail pressure high enough to inject ?

Haven't a clue, I hadn't really considered that it could be down to a lack of pressure.

It previously died with exactly the same symptoms and that was due to a broken wire on the fuel metering sensor, which is just next door to the one I have changed and on the same bit of loom (I might have called that wrong I am just trying to remember what the garage told me). last time the garage repaired it as it broke down on the road and I got it recovered to there, the same garage code read it this time and pointed me at the fuel pressure sensor.

How would I test if the pressure is actually high enough?

The pump in the tank supplies fuel.. just like with a carburettor

However the diesel needs MASSIVE pressures to inject and run

Cranking should give @250bar
Running will be thousands..

The sensor should give data visible via the OBD port - near the steering wheel

There are chances of either.. a failing HighPressure pump..

OR a good pump.. but dribbling leak..
So fuel pressure lost..back to tank..or into the cylinders


Can the garage give you rail pressures?

Seen lately..and seen now

Oh dear, that doesn't bode well for me. I'm stuck with the van at my house now as it wont run and I don't have access to an ODB reader to check the pressures myself. Not sure what to do next...

Johnson4130 said:

Oh dear, that doesn't bode well for me. I'm stuck with the van at my house now as it wont run and I don't have access to an ODB reader to check the pressures myself. Not sure what to do next...

Click to expand...

IF you feel confident to do it safely ..

Towstarting can get the motor spinning quicker than on the startermotor

More speed : more pressure

Look here to see if somebody is local:


https://www.fiatforum.com/multiecuscan-members-register/

Charlie - near the M4

varesecrazy said:

IF you feel confident to do it safely ..

Towstarting can get the motor spinning quicker than on the startermotor

More speed : more pressure

Click to expand...

Hmm that sounds scary haha,

I measured the new switch and when the ignition is on I am actually getting a tiny voltage on the red and green wire, about 0.018v. although its small its definitely different to when the ignition is off making me think the sensor is picking something up and from watching a how to video for a similar sensor the voltage seems in the right range. Can anyone else who's had the issue or knows more about it verify if my numbers are right or wrong?

Can you post a couple of pics.. so we are definitely testing the same thing

Thanks for having a look, this shows the plug close up and a wider view of the fuel rail with the plug on the left end of it. I got a friend to come round with an OBD reader but unfortunately it was just a basic one so couldn't tell me the pressure at the sensor :/ I'm going to try another one tomorrow that supposedly goes more in depth and hopefully that will give me the answer.

Ok i think the problem is actually nothing to do with the pressure sensor, I just tried cracking one of the pipes that go to the injectors and turning the ignition on to see if there was any pressure there, there was not.
After a few tentative goes i unscrewed the locking nut totally and when the ignition turned on no fuel came out of the hole in the fuel rail (there was a tiny dribble as you would expect from gravity but there was no pressure whatsoever)
This makes me think the pumps are not even getting the signal to fire? any idea where to start looking with that?

Does the car recognise the Chip in the key..?

Another possibility is the Fire Prevention System..

And bumps will cut power to the pump in the fuel tank..

Is the diesel filter under the bonnet still getting fluid?

varesecrazy said:

Does the car recognise the Chip in the key..?

Another possibility is the Fire Prevention System..

And bumps will cut power to the pump in the fuel tank..

Is the diesel filter under the bonnet still getting fluid?

Click to expand...

I had problems with the key chip before and it showed the immobilizer symbol on the dash which it isn't doing now so i'm pretty sure that's all good.

no idea about the fire prevention system

its not had any bump apart from pushing it onto my drive but i have driven it on the same way 100s of times. that's the inertia switch that cuts it out after a bump right?

not sure about the filter, ill try removing a line there and seeing what happens.

Thanks for all the replies by the way, really appreciate the help. I'm pretty good with mechanical things like suspension and brakes and replacing head gaskets etc but i've never messed about with this sort of problem before

You are very welcome.

A great deal of this comes via the forums excellent SEARCH.. and owning and maintaining cars myself

Always something new to learn

ok been away from this for a few days due to buying a house and some crappy weather but back on it now.
I have removed the covers for the fuel lifting pump on the tank and when you turn the ignition on it doesn't make any noise at all. I unplugged it and tested for voltage on the plug and there wasn't any but I am not sure that this is a true reading though as the fuel level sensor is on the same plug so it might not try to run if it thinks there is no fuel. either way it seems to me like there is no power going to the fuel lifting pump.

How do i go about finding the relay/ fuse etc that powers the pump? anyone know where I can buy a decent manual online with wiring diagrams etc?
cheers
James

I found a fuse box diagram and checked the fuse for the lift pump, it was ok and there was voltage at one side with it removed.
I couldn't find a relay diagram but i have tested every relay in the engine relay/fuse box and they were all ok (i checked resistance across the coil and then applied 12v to the coil then checked resistance across the contacts to make sure they closed)
Unless the relay for the fuel pump is elsewhere it must be ok. any ideas what i can check now?

I have now tried wiring the lift pump up to a 12v supply directly, it works! Am i right in thinking the pump should activate for 10-15 seconds every time you turn the ignition on?

I'm now thinking there must be a broken wire between the fuse box and the fuel pump

scratch my last post, i tried the ignition again after plugging the pump back in and it does actually do a little bump but doesn't run for any length of time. I have removed the fuel filter and tried the ignition again and same thing, shoots about 20ml of fuel into the cup i have under the end of the line then cuts out. blocked strainer in the tank or something else electrical maybe?

Your rail pressure sensor is back in the frame..

If it says its 'full' pump demand is off