Has anyone else had this problem? 2004 MCS is VERY sluggish under acceleration. I have no warning lights and no fault codes. Idle is smooth and mpg is normal. It will rev all the way to the limiter, but takes FOREVER to get there.
Air filter is clean, replaced injectors, plugs and wires with my spare set...no change.
The dealer examined the car and stated there was too much ethanol in fuel. I have used the same brand fuel (Shell) from day one. I have run 3 more tanks from 3 DIFFERENT Shell stations with no change. NOT buying the ethanol theory at all.

2004 MCS, 76 K miles, 15% pulley, 2% crank pulley, CAI, JCW injectors. All parts have at least 15,000 trouble free miles on them.

HELP!

 

You need to go to the dealer immediately and trade it in for an R56 model.

 

supercharger failing?? pulley slipping?

 

try the 1st Gen section. I know the ECU on the 2nd gen can get thrown off and not allow any boost at all in a sort of safe mode, but that it should be fixable by turning the car on and off and it does not throw a CEL.

OOOOh, Cat maybe? Is it getting worse? I had a Cat plug up on a GN partially, and it had symptoms similar to that.

 

I like the cat plugged theory, as well as the possibility of a boost leak. BUT, the #1 thought in my mind is a faulty bypass valve. Sounds like it gave up the ghost. Vacuum/ boost driven, and it won't throw a light. Might try testing it first by wiring it shut, then if that fixes it, ring me up for a Detroit Tuned BPV.

Good luck!

 

Ditto Adams theories. Busted bypass valve or plugged catalytic converter are most likely.

 

I really appreciate all the help. I’m going to check that bypass valve first since that’s easier than the cat! I’ll let you know.
Thanks again,
Russ