Noisy fuel pump - pressure too high

[Swotty]

Hi everyone,

W215 CL600 TT

The fuel pump had always had a whine since purchase, so took it into Mercedes over here who diagnosed new pump + filter needed, so had them replace in February. Not cheap.

Sound didn't go, so took it back last month. They say the pump & filter is fine and proposed to drain the fuel tank as perhaps the filter at the bottom was blocked.

Have done this and ..... noise still there.

They now say there is too much pressure in the fuel system (7 bar v normal 3.5 bar) and need to look further.

Any thoughts? They say the pump is whining as it's having to work hard to deal with a blockage ......... presumably now, that's further up the line ..... anyone had a similar problem, please?

Thanks,

Stuart

 

[John Jones Jr]

I've no knowledge on your particular engine but the issue points to a faulty FPR (fuel pressure regulator) which by the way is generally controlled by engine vacuum and they cost sub £40 for a Bosch unit or the issue could be a blocked or kinked fuel return line which I'd doubt.

What's really annoying (bar already incurred cost) is why the dealer didn't do a basic and simple fuel pressure test first.

p.s Just to add there could be a fuel pressure sensor fitted to that engine, if so that maybe that's issue. I can't expand any further simply due to lack of knowledge specific to your engine.

 

[Deleted member 65149]

Unlikely to be the same problem, but it reminded me of an issue I had with a BMW 520i many years ago. Soon after a full service I drove to Austria and noticed a strange noise from the back of the car whilst on the autobahn. Whilst checking out the noise I noticed that the fuel filter was fitted the wrong way round - the clue being a big arrow on the filter pointing towards the petrol tank. On returning to the UK I went back to the main London BMW dealer where it had been serviced. They checked it and said it was fine. I refused to accept this and persuaded them to let me point out the problem while the car was still up on the ramp. They continued to deny the filter was wrong so I had to persist. They eventually agreed thanks to intervention from another service team member. They even said, "We'll turn the filter round at no charge"! You can imagine my response. But they refused to replace the fuel pump that had been under strain for a couple of thousand miles. That was the last BMW I ever owned, even though the noise stopped and there was no further problem with the pump.

 

[Lyserman]

I am in total agreement with John Jones Jr.
Basic engineering says that if a suction filter is blocked you get low pressure and something on the discharge side blocked gives high pressure.
Either the fuel pressure regulator is stuck or the return line is blocked or crimped.
It makes me wonder sometimes the competency of "techs" these days.

Hope you get it sorted.

Tony

 

[Swotty]

Thanks, guys.

Yes, I wondered why it took them a while to diagnose the high pressure in the system. Being wary of the way Mercedes main dealer costs can escalate, I got a "devis", which is a binding estimate, before putting it in. They will have had it for 3 weeks come next Monday (Friday is a bank holiday over here). They have full STAR facilities, so dunno why they couldn't pinpoint the fault straight away.

Will ask them about the fuel pressure regulator tomorrow and also check that the filters are correctly fitted.

Thanks again, and will post an update.

Stuart

 

[John Jones Jr]

Will ask them about the fuel pressure regulator tomorrow and also check that the filters are correctly fitted.

Don't forget to ask them about the fuel pressure sensor too.

 

[Swotty]

Don't forget to ask them about the fuel pressure sensor too.

Yes, thanks, John, have done so. They say they have lots of work on at the moment and will look at it again shortly.

They've only had it two and a half weeks!

Stuart

 

[Swotty]

Sorry to take so long to report back.

Very long story, starting with them saying the fuel pressure regulator and sensor were fine, as were the fuel lines.

Just under 6 weeks later and after advice from MB Germany, they changed the sensor ........ bingo!

They did not charge me for the extra and unproductive work, but I was without the car for just under 2 months overall. I did have a courtesy car, but it was a dirty and dented Yaris.

The sensor had to be ordered specially (so they said) and it took over a week to arrive.

My advice to anyone with this kind of problem is to change the sensor, for what it costs.

Downside is the economy is way down, but may be due to the cold weather here at the moment.

Thanks again to everyone for your spot-on advice. This forum is really helpful and knowledgeable.

Happy New Year to all,

Stuart

 

[John Jones Jr]

Good to hear you're now sorted. But honestly it seems shocking to me that a main dealer took so long to sort the issue, I'd reckon a faulty fuel pressure sensor is basic stuff to a competent dealer, M-B specialist or even a general garage. I'd strongly advise you locate a good M-B specialist for your own peace of mind and pocket.

 

[Swotty]

Thanks, John.

Unfortunately for me, that garage IS the Merc service centre for miles around here. The only bigger ones are in Bordeaux or Toulouse, which is a 2 hour drive and then madcap city centre mayhem. It's one of the drawbacks for living out in the sticks here ....... and why everyone drives Renaults, Citroens and Pugs.

A friend has now bought a computer diagnostic kit for his SL and SLK and has offered me use of it, so I'll be taking him up on it, I'm sure!

The car is absolutely brilliant but had only done 46K miles in 11 years and had been stood around for long periods. Despite having full and timely servicing, I'm told these need regular use and am doing my best (!) but am playing catch up.

Thanks again,

Stuart