REF/////C63

Hey guys - new to MBWorld but I've been checking in every time I have an issue with my C63 (i.e. frequently). I've had the car for 3 years and it has about 67k miles.

A month ago I brought the car in for CEL code 2540 - low fuel pressure. The intake manifold gasket was leaking and was replaced by the dealer under warranty. I've driven the car about 1,000 miles since then and on Sunday got CEL code 2540 again. I brought it to the dealer and the shop foreman can't figure out what's wrong with it - they've had it for 3 days. He clears the code and it keeps coming back on, but they insist the fuel pressure isn't low. Service rep said Mercedes NA is sending someone out to assist. I'm concerned because my extended warranty ends at the end of this month and it looks like I'll have a lot of expenses in my future at the rate we're going, but I love this car too much to get rid of it. I've already replaced the fuel pumps about 1.5 years ago for the same low pressure issue. Probably also worth noting I've already had the headbolts and purge valve replaced if that helps. I've checked the threads and it doesn't seem like anyone's posted a resolution to this type of fact pattern - seems like I've already replaced everything that could've been causing this issue. Would greatly appreciate any thoughts (besides buying the W205 C63 that is)!

qjumpr

Have you replaced the fuel filter? Mine ended up being that for a low fuel pressure code. The actual plumbing in the tank from the fuel pumps was almost black on the inside. Looking at it I didn't think that such a small reduction in pipe diameter from the sludge could have done it, but once I changed the filter the light went out and has been out ever since.

Part cost me $449.

Like you I had changed all the usual suspects and using a fuel pressure gauge at the fuel rails also showed the fuel rate was perfect. Turns out there is a sensor in the filter assembly, and I'm guessing that was causing the code.

REF/////C63

Thanks for the suggestion. They have not replaced the fuel filter or the fuel injectors. They've tested both and said they were fine. I just called this morning and insisted that they replace the fuel filter - hopefully that's what it is!

REF/////C63

Just heard back from the dealer - fuel filter was replaced and CEL code 2540 still coming on. They still can't figure out what's wrong with it...not sure where I go from here. Only other thing I can think of is to tell them to replace the fuel injectors but they told me it would be a different CEL code. Thoughts on next steps from here? Thanks again for the insight.

qjumpr

Next step would be data log and get out the volt meter, if they haven't already done that. Maybe there is a slight blockage in one of the lines from the PCV, Fuel rails, injectors etc. If you do a search all of those have caused issues.

The hard part is eliminating all the electrical possibilities. It could even be a sensor, and maybe not the Fuel pressure one on the fuel rail. They may have even knocked a wire loose when replacing some other parts. Even the O2 sensors can effect fuel pressure and data logging would show range values for that.

If they find out the final result let us know.

solekeeper

lets say the dealer can't figure this out, what happens?

Missionary

Thought about putting it on the dyno and having the shop confirm the pressure across a power run with a fuel pressure gauge to rule out the sensor?

Has the voltage at the pump being checked unplugged and with it running? If it is low there will be a voltage drop somewhere. Relay perhaps?

I would just build a case, take the proof to them and say fix it. How should not be your issue.

betrezra

We had this issue on my wifes 2014 C63 with only 250 miles..... it turned out to be the fuel pump p/u disintegrating and plastic bits plugging up the p/u....... have them put a fuel pressure gage on your ride as they drive it and watch fuel pressure under load.

New fuel pump and she was good to go. Something to consider.

layzie12g

We had an ML63 with issues that had a fuel pump replaced. Turns out it needed another one.

REF/////C63

Thanks for the thoughts, all. Just got it back from the dealer today. They replaced the fuel pumps (both main and auxiliary, for the second time as they were both replaced about a year and a half ago), the fuel pressure sensor, and the mounting plate. Put about 150 miles on today and it looks like we're in the clear. Warranty ends in 10 days so things are about to get interesting!

qjumpr

Glad you got it fixed, between the new pumps, filter and everything else I'm sure its good to go!

I am Jeff

Don't worry about the expiring warranty. Since you have brought this issue to the attention of your dealership prior to the warranty expiring, MB will address this issue as a sign of goodwill. I've had items replaced under warranty even though my warranty has expired.

betrezra

Good news!

REF/////C63

Very good news indeed!

UPDATE: I brought the car back on Monday as the sensor for the front brakes went off on Saturday (day after I picked it up - slightly suspicious but I'm due so I'll roll with it). While it was there, they checked fuel pressures again and said that while the CEL wasn't going off, they wanted to replace the injector seals just to be sure I don't have any issues. That means they're also going to need to replace the intake manifold gaskets again since they'll be cracking it open to take care of the injector seals. Can't tell if they're trying to print money or if I've befriended the shop foreman and they're trying to do what's right - I'm hoping the latter. I'll keep everyone posted.