I hope this is nothing major! I don't even know where to start looking for the issue. I had that red battery light come up one day and replaced the battery just to find out it was the alternator not keeping up with the Voltage requirements. So I replace the voltage regulator behind the alternator and that worked fine for normal driving but at WOT i would get the Red battery warning light. I replace the alternator with a new this weekend and now voltage is perfect 13.9-14 at idle and stays the same at WOT. But the car is not making power smoothly it cutting and out every other millisecond.

I'm thinking it might be a fuel pump? I'm not throwing codes so I don't think it's the ignition. Also I don't hear any knock so maybe I have a electrical problem?

I did replace the alternator with a brand new Bosch unit

Thanks in advance for any help you can give me.

Just a quick update. This morning while starting the car it ran rough so I think I have a fuel pump failure. I can't find online where the relay is to see if it's a cheap fix or do I need new pump. I found where the rely is on the e500 next to the navi cd disc player but also read the e55 has the rely in a different location because it has two pumps so MB need to wire the car differently.

What steps do I need to perform to identify which pump is failing?

Thanks
Eric

It will feel that way if the supercharger belt is slipping at WOT also.

I didn't have any rough running when the pumps were dying.

Relay is right hand side, behind the paneling in the boot. Mine was the top relay and was obviously damaged.

How did you know your pumps where dying if you didn't have any jerkiness?

I have just been through this whole fueling process in my car.. Man what a nightmare trying to diagnose everything... But yes if car is jerking and bucking like a rodeo under throttle then I would start with fuel pressure. It's likely to be the pumps. The relay will be on the right hand side of the trunk, behind the paneling. Mine was the centre relay.. In a cls55

I was like most other people. My filter/sender unit had cracked and was leaking fuel into the car. After I replaced my filters and pumps, I had one more instance of the car stopping, just cutting not jerking. That was due to the relay in the boot having been damaged by the old pumps causing over current draw.

Once that was replaced the car hasnt missed a beat. I've been wrong before, but I wasn't under the impression that the pumps necessarily 'failed', they just leaked. I've had jerkiness in a car from a bad fuel pump before, but it isn't quick on and off feeling. It is fine, fine, then the car will fall on its face, then quickly be fine again.

Yip that makes sense. My car would be fine under normal acceleration, as soon as you hammer it, it would fall on its face, bucking around... Fuel pressure would just be dead... So have replaced both pumps now.. Car needs a retune we think as it's still not 100%.. All relays are fine

Thank you for the suggestion, I don't think that is the problem because I data logged boost and it's steady. I do get belt slip in 2nd gear boosts between 13.8 to 14.x but I don't get it in other gears so I don't think thats the problem. I will say that 2nd gear belt slip is still very smooth compared the issue I'm having.

Ok So

I checked the Fuel Pumps all good over 80 PSI at idle. (YAA)
Replaced the serpentine belt with a new tensioner (little better still have the rough running)
Jerry at EuroCharged suggested I check the alternator electrical connections just to rule that out and I did and reinstalled them and check the wires. That looks good.

So Now I think it's my IC pump or I need the bleed the system. I had to remove the radiator hose to remove the Alternator and thinking I should have bled the IC system .

I have not had a chance to really data log the IAT so I will do that and confirm what I'm thinking.

Any other suggestions?

Thanks!

If you're checking your fueling, don't neglect the fuel sender (opposite side of the tank from the pumps). It has an internal fuel filter that gets pretty nasty.

Thanks for the heads up

Speaking of that, I have just pulled that fuel filter out.. Tech reckons don't need it... So we just left it out.. Anybody else done that?

I found my issue and fixed it today. It was supercharger beltslip. Thanks for all the advice.

Just changed my belt

Glad u found it. That was my first thought