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Old Aug 13th, 2014, 05:03 PM
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Question Poor performance issue finally resolved??

This might help anyone with poor performance issues with their R56 Cooper S\JCW.....

I've just booked my JCW (2008) in to an independent BMW specialist to investigate an on going problem since I bought the car 15mths ago.
It's never really run smoothly particularly when changing through the gears, (it seems to lurch in to gear 2nd-3rd), and sometimes hesitates for a split second under acceleration.

So the history looks like this...

I took it to one independent garage a few months ago to check this out, and they reckoned there was an air leak under boost. They did a smoke test, and the test showed no air leaks, but the mechanic mentioned for a JCW, the car didn't feel that quick when he drove it. (It is a genuine factory model)
I didn't know any better, as I was used to the power it was producing.

I then took it for a diagnostic check on a rolling road, and although no faults were found, it was apparently only pushing out 175bhp at the wheels.
This seemed odd, as this is the bhp for a Cooper S.
I was told Boost levels were good , and everything apart from the power output looked fine.
It was then suggested that maybe sometime in the car's history, the ECU was remapped accidently with a Cooper S map, and I should book it in again to have the ECU's software downloaded to check the validity of the current map.
If it confirmed I had a Cooper S map, they would then remap to a JCW map at a cost of 300. I checked this with BMW, and they said that was highly unlikely.
Now, I wasn't present at the Dyno test, and I didn't get a print out of the results either, so I suspected they were pulling a fast one, and I left.

So now at the Specialist garage, they have found that the High Pressure fuel pump isn't working to max output, and this was the reason for the lumpy and poor performance. They replaced the HP fuel pump, only then to discover an air pipe to the turbo had a blockage, and that too needs replacing as the boost level is too low.
I asked why the low boost is now apparent, and not detected earlier, and they said because the fuel pump is now producing the correct pressure, the boost can't cope because of the blockage, and is producing a low boost fault code.
The air pipe is now on order.....
The saga continues...

I'm picking the car up tomorrow, so will report back with the results..
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Old Aug 13th, 2014, 09:53 PM
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175bhp would be a flywheel figue for a standard Cooper S, so if you got that I'd estimate 20% transmission loss so you'd be bang on the money for a JCW flywheel reading.
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Old Aug 14th, 2014, 08:51 AM
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Quote: Originally Posted by k3fus (original)
175bhp would be a flywheel figue for a standard Cooper S, so if you got that I'd estimate 20% transmission loss so you'd be bang on the money for a JCW flywheel reading.

Ok, thanks. That's reassuring
Makes me wonder though why the Dyno guy said it was down on power, and questioned the mapping? I understand what you're saying, but surely they would tell me the same.
He too reckoned it felt 'flat' when he drove it. Which was probably the effect of the HP fuel pump.
It was the remapping comment that got me concerned.

looking forward to picking the car up later...
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Old Aug 14th, 2014, 01:20 PM
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Thats the max reading, theres a lot to learn from comparing the results across the whole rev range. Low fuel pressure could easily be your issue, whilst the max numbers look ok.
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Old Aug 14th, 2014, 03:46 PM
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Well the car won't be ready until tomorrow now, but the garage decided to have the car Dyno tested elsewhere, to check if the performance was restored, and the figure was 186bhp at the wheels.

They reckoned if driven on the road with the assistance of forced air, it would add another 4bhp.
The target figure I was told, should be 192bhp apparently.

So am guessing the official 211bhp would be at the crank?
This is a factory JCW, not dealer enhanced.

I'm hoping 186bhp is ok, as I just want to make sure I've finally got the car sorted.

I will be able to tell if it feels any better once I get to drive it.
Fingers crossed....
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Old Aug 16th, 2014, 05:55 AM
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Ok, picked the car up yesterday, and the jerky gear changes have gone.
Smoother running now, but performance remains the same .

Having seen the dyno data sheet, I see 186.3bhp was at the flywheel, so I'm still down on power somewhere!

Will have to do some further investigation.....

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