Rick X Joaquim

BiturboSF

I've noticed this happening on my '13 as well, I did not have this issue on my '09 C63. As soon as I fill it to full with either 91 or E85 (I have the flex fuel kit) it pulls incredibly strong, & like yours, once the needle drops pass the middle mark, the car feels sluggish. Initially I thought it was the gas going bad however I burn through a tank in 3-4 days, so that shouldn't be enough time for the gas to go bad. All my fuel injectors were also replaced 3 months ago as preventative maintenance, the fuel pump was also on the back of my mind. However I didn't want to blindly replace it without really knowing the problem, I just hit 60k miles on mine.

Funkwagen

I've noticed this recently and then threw a code in the past week for fuel rail pressure. The CEL came on but then turned off about 30 minutes later and hasn't shown since. The car still runs no problem but I do notice the occasional hiccup when the fuel tank is below 1/2.

Does anyone know what the fuel pressure is supposed to read around while the car is running? I'm having issues with my STAR diagnostic system right now (waiting on parts for my laptop..), so I can't check in Xentry.

My car is at 135,000km at the moment, started showing signs of this around 134

Vladds

which code, what's the number?

Funkwagen

P2540

FactoryFast

whats the interval for the fuel filter...id try replacing that first...

jptaylor

There is no serviceable fuel filter on our cars, the pump has an inlet sock and also an integral filter that is injection molded inside the fuel pump housing as it is being made. Tasos did a video where he tried to get at the internal filter and was only able to destroy the fuel pump assembly in the process.



As for the issue the OP and others have opened up here I think that the answer is pretty clear. Electric motors run very, VERY efficiently....under the right conditions. The primary condition that must be met is temperature. The hotter the motor gets the less efficient the motor pumps. Conversely the age/condition of the motor itself contributes to the motors ability to run/work without producing excess amounts of heat. Once the fuel pump motor wears to the point where it is producing a little extra heat in order to perform to the same level the engine was demanding when the pump was new it will require some outside assistance in staying cool enough to output 100%. The primary method of cooling for your fuel pump is the gasoline under which it is submerged inside of your fuel tank. When you fill up the tank with gasoline your fuel pump has a nice big pool of very high efficiency heat transfer fluid within which to dissipate any additional heat it is producing. Once your gas tank level drops to say the half full point your fuel pump is still being tasked with outputting the same demanded pressure/volume/etc but now only has HALF as much external cooling capability as it did when the tank was full. Once you see this scenario happening under these conditions your only real option to remedy the problem will be to change out the fuel pump assembly. Fortunately on our cars it is really not that big of a deal and even a basic wrencher can handle it in under half an hour or so(its underneath the rear seat and VERY accessible).

Rick X Joaquim

chrisridebike8

I had to replace both fuel pumps around 90k miles. My symptoms were initially hesitation under part throttle. The car would chug a little bit going uphill or going from say 60-80 mph on the freeway without forcing a kickdown. Then the hesitation got worse. Then the car would sometimes stumble at constant speed like it died and then came back. Then the car would sometimes die trying to leave a stop. I took it to HG Motorsports and they said the pumps were drawing too much voltage at idle and then not enough at part throttle. I also had a check engine code that popped once, P228F and P229F if I remember correctly. Once the pumps were replaced, the car was back to normal. The fuel sending unit was not replaced, but I wish it had been since the fuel filter is in there. I am thinking about replacing that now just as a precaution.

chrisridebike8

also, if you are a DIY type, those covers under the rear seat are hard to get off without the tool to remove them. Amazon sells a universal one for like $15 which is worth it.

Fabioppp

Hello, did the car sound different?
I’ve been having a problem with my 09 car after I tracked it it had a fuel pump engine light. And car lost soul, deep ness and acceleration.
the engine light still comes on when pushing the car.

could it be the fuel pump because I was also considering could be distribution but no errors on that end. All been checked and good.

Been trying to solve this issue for a year.

thanks