My wife came home today and said the MINI was acting up/ stumbling at take off. I went out to drive it, and it's definitely stumbling while accelerating. It idles fine, but if you give it alot of gas it stumbles/hesitates while trying to rev. It was doing the same a couple of weeks ago, and I replaced the fuel filter, but now it's back, and I suspect the fuel pump itself. Any thoughts?
Thanks

 

How about a little more about the Mini. Year, miles and other pertinent data. That would be a start. I'm assuming there are no warning lights? If there are not then I would get it scoped. It could be several things beside the fuel pump. You could be chasing for awhile and wasting money.

 

Any CEL's ?

1) Spark - coil, wires, plugs
2) Fuel - injectors, lines, filter, pump, fuel pressure regulator on fuel rail.
3) Bad DME.

First two good areas to start with.

Check the items in #1 - But after that it is a situation that without a code, you could be chasing this down for days and $$$$$ later. Mechanics have devices to measure any pressure losses in the injection system, and could diagnosis this alot quicker and maybe even cheaper for you in the end.

 

Sorry, wasn't thinking. '05 Cooper S, manual, 85k. Only mods are a 15% pulley and Borla exhaust. I'm taking it down to get the fuel pressure checked now.

 

Fuel pressure tests ok: 53 psi key on, 45 at idle, drops to 42psi when revving it. Any ideas? No one can look at it until Thursday

 

Solved it. Decided to check the plugs, two were 3-4 turns loose, so I decided to change them out (they were replaced 20k ago). Runs like a champ now.