Fuel Pressure Way Too High

[French Jeff]

I'm looking for some advice please. I have a 2007 Viano 3.0 CDI. I have an engine warning light displayed and have most of the time much reduced power (especially when hot and when the auto gearbox changes down). I am told that the fuel pressure is normally around 260 bar, however two mechanics who have tried to diagnose the problem have told me that the pressure is between 800 and 900 bar!!! It has been suggested that a Sensor is faulty, however there are 3 related sensors so I don't know which to try 1st. Anyone have experience of this issue that could shed some light on the solution please?

 

[Craiglxviii]

I don’t think... no, I’m absolutely completely certain that the high pressure fuel pump is mechanically unable to get rail pressures that high. It might have a 7-10% reserve margin in the design, but that’ll be it. Not a 350% margin.

Yes, there will be a faulty sensor. The first thing to do is to get your car on a Mercedes diagnostic system and have the fault codes read. Cost around £60 at any decent independent garage. Where are you located, perhaps we can recommend a garage..?

 

[French Jeff]

Thanks. I tried that and took it to a Garage where the head Mechanic worked for Mercedes for 10 years. He didn't specify the error codes but suggested that there were several problems, that he was not prepared to do the work and that my best option was to replace the engine and turbo - hence my local Mechanic is trying to have another attempt at resolving the problem. I'm currently in SW France and hence trying to have it dealt with here. I'll translate the ex. Mercedes Mechanic's Report and post it here in a few minutes.

 

[French Jeff]

Now that I think of it, the ex. Mercedes Mechanic did show me a photo that he took of the error codes. I am puzzled by the fact that, having had the problem for several months, 3 weeks ago I drove about 2 hours North and had to stop multiple times as I was reduced to a crawl while on the Motorway. Bizzarly, before I returned several days later the power suddenly returned and I had it for 13 days and then suddenly it was gone again!!

 

[French Jeff]

The Mechanic's report said that he identified problems with: Turbo, EGR valve, air conditioning pipe, engine harness, exhaust leak, air suction pipe, significant oil leak in various places.

I am puzzled by this as the Turbo seems to be perfect but there is an air leak somewhere. There is also not a single drop of oil on my driveway so I am very puzzled about the suggestion that there are oil leaks. Being 2007, it had the problem with the original oil coolant seals which were replaced several months ago which is when this problem surfaced so I am wondering if something was done wrong when the turbo etc was reinstalled (all the seals were replaced).

 

[LostKiwi]

Where in SW France are you? We're hoping to be back there in October and I can read codes for you if necessary.
We're an hour north of Bordeaux.

Split boost hoses are common as are rotted intercoolers (though probably less prevalent in France due to unsalted roads).

An oil leak on the inlet manifold seals can cause oil to drip on to the boost actuator and cause issues with it, the swirl flaps and EGR from memory.

 

[mersum1es]

About fuel pressure, commonrail pressure are up to 1600bar so nothing drastic there...

Problem is that you mechaninc is doing diagnose by device which is not copatible with MB (no, it isn't, whatever he says, if diagnose sounds like lottery).

As above boost line tightness is 1st check (and like LostKiwi said, EGR and swirl flaps are included in boost air 'route', and gives opportunity to leak spots). Hehe, what I actuallu said ...

If turbo seal has been installed badly, it will eventually cause problem and in worst case turbo failure.

 

[French Jeff]

Thanks for your replies. LostKiwi, I am about 2 hours South of Bordeaux but happy to make the trip North so if you get back please let me know.

 

[axelcls]

Hi Jeff, you’re 2 hours south of bordeaux , tolouse maibe ? I’m in north Italy at the moment, in Ventimiglia in holiday, I have a iCarsoft pro in my car and if’s not to far for you just let me know. I’ll be here for 3 more days, Alex


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[French Jeff]

Hi Jeff, you’re 2 hours south of bordeaux , tolouse maibe ? I’m in north Italy at the moment, in Ventimiglia in holiday, I have a iCarsoft pro in my car and if’s not to far for you just let me know. I’ll be here for 3 more days, Alex


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Many thanks for the offer Alex, unfortunately I near the Atlantic coast! Enjoy the holiday.

 

[axelcls]

Sorry, thank you


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[Craiglxviii]

Wow, that’s some serious freebie help offered. Well done you guys!

 

[French Jeff]

Update on above. Both related sensors were replaced but it made no difference! I have it booked in with Mercedes Bayonne next week however due to the number of issues the chances of them offering to do any work are slim to none! My local mechanic bought himself a new diagnostic tool this week and plugged it in yesterday evening and the photos show the codes displayed. Any educated suggestions would be welcome please.