TD4 fuel pressure info required

Hi all, been trying to fix the white smoke at 1800 problem which looks fairly common on the facelift models but there have also been multiple fixes but can afford to try them all, I have been advised to check fuel rail pressure and harness which makes sense but OBD doesn't seem to read frp on a couple of different units .
so here's the questions
1 if I unplug the fuel pressure the engine stutters but keeps running and no dash light - is this normal ?
2 with the sensor unplugged what the default rail pressure ?
3 what's the minimum and maximum rail pressure in comparison ?

tp/maf/map/iat/ect/v all seem steady so knowing these answers might help find the problem

1: The engine will run with the rail sensor unplugged, although it'll run badly.
2: With the rail sensor unplugged, there's no way to read the rail pressure. If there's no rail sensor signal at the EDC, there's no live data available on the diagnostic device. The EDC most likely substitutes a default value or the engine would stop. However very few people would know what that default value is. It'll be part of the EDC programme.
3: Min and Max rail values vary between engines in normal running. However ballpark figures would be about 25,000 Kpa at idle to around 115,000 Kpa at full power RPM.

Thanks Nodge, yes default pressure is going to be a difficult one unless we have a specialist on the site - what about the dash light if you unplug it while it's running should it come on or stay off ?

There's the injection data.


From memory. A bad connection on the rail sensor, doesn't activate the MIL.

I had a light and almost zero power with a dodgy connection on the fuel rail sensor. Funny thing is the engine warning light came on some times but not every time. I was fitting a Ron Box at the time and a quick reseat of the sensor sorted it but had me worried for a few minutes, the car ran fine on first start up, then after moving out of the garage it ran like a dog..

Thanks Alibro, if you ever see the white smoke thread it's a bit odd that so many members have had this but not found a common cause, like so many others I don't want to throw money at it blind

Been looking on the net for info on the Turbo solenoid valve but don't seem to be able to find some simple information so could do with some assistance please.
The three connectors go manifold vacuum at the top - turbo in the middle and vent on the bottom. so the question is on tick over is there vacuum at middle bottom or both ?

The top pipe is the vac feed from the reservoir.

The middle goes to the turbo vane actuator.

The bottom goes to the vac filter.

Thanks but if you put a vacuum gauge on middle or bottom what should I see at idle

Greg Storm said:

Thanks but if you put a vacuum gauge on middle or bottom what should I see at idle

Click to expand...

Nothing, or very little.
The vac solenoid connects the vac feed on the top to the vac actuator on the middle, when the EDC energizes the solenoid value. When the electrical power is removed. The vacuum in the actuator is returned to atmospheric pressure, by joining it to the bottom pipe connection. There's a filter on the end of this pipe, to stop debris getting into the solenoid valve.

Thanks Nodge, what I am finding is full vacuum on top (-30inHg) as expected and around -6 on the middle actuator line and a slow build up of vacuum on the bottom breather line. So I assume all that vacuum has to be going somewhere and I've tested the actuator and line so it's not there but unless there is some form of internal bleed then I assume the solenoid is leaking or am I missing something?

Is it just a simple on off solenoid or a variable valve like a idle valve

Your vac readings seem about right. There could well be up a small amount of bleed through from the 30Hg to the open vent. I don't think it's a big issue. It's designed to allow a small amount of atmospheric air in, that's why there's a filter there.
The vac actuator is modulated by the EDC. This enables it to very the boost given by the turbo.

Thanks - found a video of one being stripped so can see how the top chamber and plunger in the armature works. I think last thing to do is take a physical reading of the manifold pressure/vacuumed to rule out blockages or boost just in case the obd is out. Is there a way to get the ecu to recalibrate to a base setting.

Are your vac pipes in good condition, they are know to perish and collasp internally, especially the long one from the vac reservoir.

pipes seem ok, did a leak off test but had 3 pass a lot more than 1. how would you know if you had 4 knackered injectors is there a volume over time or do I need new injectors?