yoyo/surging feeling under acceleration

[S-Cooper]

Has anyone else with their Cooper S experienced a surging or yoyo effect under fairly heavy acceleration from being stopped between 2000-4000 rpm in second and third gear?

[Johnboy]

Just out of curiosity, does this happen with the air-con turned on AND with the air-con turned off?

J.

[S-Cooper]

It is more noticeable with A/C on and is only felt with heavy but not to the floor acceleration. It's not felt under very light acceleration.

[Johnboy]

Hmm.. Guess that blows up that theory then!
It's just that on the normally aspirated Cooper, I have noted that the air-con affects my throttle response in an unusual manner - I get a surging feeling when driving with light throttle on a downhill gradient, and over-revving when I lift off at high RPM.
It's also noticably less torquey pulling away at low revs.
Somebody else posted something similar in another thread about over-revving when the a/c unit is on.

It's an unproven rumour, but it was once said that the engine electronics advance the throttle slightly to make up for the air-con being on.

Obviously not affecting you though.

J.

[Sashadog]

I too, have felt a slight surging under acceleration. It seems independant of the a/c and load. I would say at about half or more throttle and around 3.5k on the tach.

[foxcasper]

Yes I felt it too - under light pedal accel in mid rev range.

I would guess its one of two things:

1) spark mapping poorly mapped - i.e not smooth transition of spark advance during the increased engine speed.

2) poor gas pedal (and engine speed) to throttle position mapping causing the throttle blade to 'yoy' back and forth.

If you can get a scan tool or get the dealer to log ignition angle, engine speed, pedal position and throttle position during the occurance - it should be obvious.

I'm not near a dealer right now - but when my local one opens I'll ask them to do it.

[Mike Clarke]

Quote:

Originally posted by spectrumm3
Has anyone else with their Cooper S experienced a surging or yoyo effect under fairly heavy acceleration from being stopped between 2000-4000 rpm in second and third gear?

This only happens in my Cooper when I am tapping my feet to TREX

[ches]

Yes, I've noticed this also, particularly in second gear, but I think it's most noticeable during light-to-moderate acceleration, and not very noticeable under heavy acceleration. It's not very severe on my S, so it's more of a curiosity than an annoyance (unlike the cold start problem).

[BruceK]

Quote:

Originally posted by ches
Yes, I've noticed this also, particularly in second gear, but I think it's most noticeable during light-to-moderate acceleration, and not very noticeable under heavy acceleration. It's not very severe on my S, so it's more of a curiosity than an annoyance (unlike the cold start problem).

Ditto for my Cooper S. Noticeable only during light-to-moderate acceleration.

[Addicted_to_S]

Yes, Stonk does this too under medium acceleration. Fortunatly, he'll be run-in soon and there'll be no more need for medium acceleration thereafter!

[An_S_4_Me]

My car does this too, very annoying!

[MINIme762]

I've noticed it too, but only when I take it out first thing in the morning. So maybe it has something to do with the engine still being cold.

Jason

[bigahead]

My MC has graduated from yo-yoing to become an experienced master of 'nearly' stalling infront of large and fast moving objects
It occurs under brisk (read 'required for conditions') accleration from standstill, often across the path of fast traffic (junctions, roundabouts, etc.),
traction either on or off, without dumping of clutch

One holiday, 9 whole days at dealership (four seperate trips), 4 seperate test drives with me and 1 mechanic / 1 service assistant / 1 workshop supervisor and 1 servicing manager (fault occurd everytime during test drives),
1 (pleasantly surprising) chat with the dealership head honcho and - lo and behold they are able to see that there is indeed a fault and it was getting worse (lower rpm).
They originaly decided to wait a month for some area guy from BMW to come and test drive it

I decided not to accept it until the problem is found and fixed, but it gives me time to pretend to be a gangster in the new 5 series they gave me until then

[macduff]

I have it on my S also in 2nd/3rd gear under medium acceleration. Talking to the dealer today, the service folks were saying that they needed the updated Engine Management software to come over before they could sort it out - could be a couple of months. Something to do with the DME - whatever that is.

ANyway, I'm going to talk with them again monday and see if I can get more information on it and if so, will post. Unfortunately I am acouple fo hours away from the dealer so can't run it down for test too easily.....

[noahe]

Yep mine does it too. Never on mild or hard acceleration, but I feel it (quite subtle) on medium acceleration. I thought it was a quirk of the e-gas pedal, optimizing the whole air/fuel/spark thing for best efficiency from millisecond to millisecond. Doesn't really bother me, but I did notice it. Mine seems to do it regardless of hot or cold, but it's quite subtle on our car.