CLS 350 CDI fuel pressure issue

[ras8963]

Hi all,
Long time since I posted here, my car was on the CLS register when I bought it new back in 2014 and 8 years 45k later I am still happy with it though it has developed a persistent problem which I was hoping someone in may have experienced and resolved.....

Initially after a full power loss the code reader identified by my Breakdown chap as fuel pressure loss.
After having the car towed to my Specialist MB mechanic this was confirmed and both pumps in the tank identified as an issue.
At a cost of around £1300 both were replaced and I left.
After the install of the new pumps I filled the tank and ran it to the low fuel light to ensure all worked well and it did....until two weeks later when I had a repeat of the power loss, returned car to garage where it sat with lots of head scratching.
My Mechanic has suggested it may be a "high pressure" pump at the front of the car, (how many pumps can a car have?), and they now need it for a further (third) visit.

Anyone experienced similar?

Thanks
r

 

[AndrewOl]

I would maybe look for another MB specialist as this one has already had a go for £1300. The fuel control systems on modern diesels are quite complex and as you have found the parts are expensive. The in tank pumps which you have changed are low pressure lift pumps which deliver to the camshaft driven high pressure pump. There are various sensors involved too, all of which can cause problems. In short you need someone who knows what they are doing or it may get prohibitively expensive for you. Either a better MB indie or a diesel specialist.

 

[ras8963]

I would maybe look for another MB specialist as this one has already had a go for £1300. The fuel control systems on modern diesels are quite complex and as you have found the parts are expensive. The in tank pumps which you have changed are low pressure lift pumps which deliver to the camshaft driven high pressure pump. There are various sensors involved too, all of which can cause problems. In short you need someone who knows what they are doing or it may get prohibitively expensive for you. Either a better MB indie or a diesel specialist.

Thanks,
The MB specialist I use is a very highly recommended one who has serviced the car each year since 3years old. For me I have £1300 in the bank if they have incorrectly diagnosed.
What I don't get is the reader should be able to identify a sensor fail as it does on all of my other vehicles….all we seem to get here is a fuel pressure fail reading…..odd.
All the Best

 

[Supernoodle]

the code reader identified by my Breakdown chap as fuel pressure loss.

I'm sure that isn't a proper fault code description. The wording is important.

What I don't get is the reader should be able to identify a sensor fail as it does on all of my other vehicles…

The ECU identifies sensor failures (not the reader), so it's probably not a sensor if it hasn't.

Even with no faults what you can do with a decent tool like Star is run actuator tests and routines to test the fuel system.

Common rail systems haven't really changed much, there's not a lot to them.
A low pressure pump, maybe a low pressure sensor (only more recent), fuel temp sensor (won't stop it working), quantity contol valve, HP pump, rail pressure sensor, injectors and pressure contol valve.
An MB specialist should be checking all these before replacing parts.

 

[TeddyRuxpin]

I'd be annoyed if a mechanic had made me spend £1300 on guesswork and still hadn't fixed the issue

 

[AndrewOl]

Sounds like they are decent guys then and should get to the bottom of it. As others have said getting a diagnostic carried out on Star (I’m assuming they don’t have it) will help no end in identifying the issue.

 

[ras8963]

Thanks all, for the responses, each encouraging.
The Garage I use is a well known, reputable MB specialist and have STAR etc…….I am however alligned with the frustration that the problem persists having been “solved” a couple of months ago.
The car is back in on Monday, beyond that it goes to a main dealer if unresolved.
Will keep you all updated.
Thanks again.

 

[Woodst]

Thanks all, for the responses, each encouraging.
The Garage I use is a well known, reputable MB specialist and have STAR etc…….I am however alligned with the frustration that the problem persists having been “solved” a couple of months ago.
The car is back in on Monday, beyond that it goes to a main dealer if unresolved.
Will keep you all updated.
Thanks again.

Did you ever get to this resolved

 

[ras8963]

Did you ever get to this resolved

Hi yes - the car was taken back in and further diagnostics identified the other pump was faulty. The Garage didn't charge me for rectifying so whilst i have a a full “set” of pumps I only paid the initial cost. Great service in the end And car har run fine since I last posted.

 

[Woodst]

Thanks for the reply local indo said they had no idea what I'm getting low pressure as star says everything is OK apart from lower pressure code how is that OK. Car with 45k and goes into limp mode if I put my gut down. Don't they actually test anything these days