My 1999 E55 has $54K miles on it and it has always run very strong. Recently I went on a 3 week vacation and when I got back, the battery was too weak to turn the engine over, and since it was the original battery that came with the car, I decided to replace it. Now, during normal driving the car drives ok, but as soon as I get on the gas I can tell that the power is not there, the shifts are not as smooth as before and at around 4K-5K rpm the enigne hesitates and does not run smooth.
Anybody else experince this before. Any feedback would be greatly appreciated.

 

The dead battery caused both the engine ECU and trans computer to lose their adaptives. Drive it hard for a couple of days. I would guess your problem will be solved. Also, it shouldn't have anything to do with a dead battery, but if you've never replaced the MAF sensor, that could be on it's way out as well.

 

Thanks for the response Fast55. I had heard about the MAF sensors on these cars. The only thing is that the car ran extremely strong before the battery died so I had guesses that it had something to do with the computer losing its settings or something.
By the I had read up on some of the threads about your supercharger. How is that working out for you. Did you get the issues ironed out yet. Since you are up to date on this, how much would the supercharger install cost now?

 

Runs good as long as it's completely warmed up. I have another independent dyno scheduled for tomorrow morning to see how it's doing. Cost of HPS is about 9K installed VS 15K+ for the base Kleemann system.

 

I had a bad battery on my 02 E55. It went completely dead in 3 days.
I replaced it with AutoZone one and I never had any problems with hesitation, e.t.c. I think you shouldn't blame the battery here.
I actually feel the car being tiny bit faster now.
(one of the cans in my old battery was shortened, so I guess it took more power away thru the alternator).

I had my adaptive system once remembered "comfortable driving settings" and I was worried where the hell the power is? I fixed it with 3 spirited full throttle short runs on the back street.

Your problem might be also in the gasoline. Sometimes even premium on good gas stations sucks, and computer can reduce power to avoid knock (detonation).