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Hesitation/Stutter on over-boost/full acceleration

125K views 39 replies 28 participants last post by  baines.j2 
#1 ·
Hi all,

I hope you can help me, my car has had this problem for some time. I took it to Mini Nottingham (Sytner's) and they, ahem, 'diagnosed' deteriorating spark plugs which they duly replaced under warranty. Needless to say it didn't fix the problem. The car drove a bit better but the problem came back.

Symptoms:

Under full acceleration and at highish revs the engine stutters badly causing a dramatic loss of power, this is accompanied with loud metallic pinging noises for the duration of the stutter (detonation?) and smoke from the rear. I have not determined what colour as yet because it's more noticeable it the dark when illuminated by others' lights and of course all smoke looks similar in the sodium/halogen glare!

If you back off the revs it's fine and probably won't do it again until the next day, for example. It seems to happen just once a day and the first time I boot it; usually when in second or third gear. It won't happen if I am tootling along in fourth or fifth - it's almost as if I need to take it by surprise with a sudden & quick increase in revs.

In addition to this the car and probably unrelated as this is more recent, the car's coolant has turned a murky grey/black colour - no smell of fuel or combustion gases though.

Any ideas?

Hope someone can help!!

Paul
 
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#35 ·
In reply to the original post....Definately pinking or pre-igniting due to carbon-buildup in the intake manifold. Solution to this is a walnut blast, relatively inexpensive and cures instantly.
The preventative is to fit an oil separator to filter out the oil vapour droplets from the crankcase gasses that are fed into the inlet manifold. over time the burnt oil deposits build up around the valve stems and valve seats, reducing airflow through the manifold and causing pre-ignition. The pre-ignition is the loud rattle noise on overboost (usually at about 3000rpm) and this results in a sudden loss of power until the ECU anti-pre-ignition software cuts in and retards the timing momentarily. You'll probably notice a cloud of sooty exhaust too.

Good luck!
 
#36 ·
I have had the walnut blasting done on my car, at a cost of £250. mine is a 2006 r56 mcs and although its better than it was it certainly hasn't cured the problem at all. I was told the car was re mapped before I bought it, is there a way to reset the ecu myself to clear the remap? i'm also looking at getting all software updated on the car as well. this bloody hesitation thing is doing my head in now. I know its possible it could also be the HPFP problem as well.
 
#37 ·
Hesitation on Hard Acceleration

Hi All,

I too had this hesitation issue. I inadvertently stumbled upon (pardon the pun!) what I feel might be the solution. I set about replacing all the seals to resolve the many oil leaks attributed to the N14 engine: Oil feed & return lines, Oil Cooler, rocker cover and the oil filer housing gasket.

As I had limited time and was working predominately from below, I addressed all but the Oil Filter Housing Gasket. The oil leak unfortunately persisted, as Murphy's law would have it, it transpire the oil filter housing gasket was the culprit. I also noticed the stumble under @ circa 3000 rpm under hard load persisted despite all the changes.

The leak got progressively worse and I started to notice smoke on warm up as oil was now dripping onto the down pipe. I therefore set about replacing the oil filter housing gasket; luckily I had only replaced the absolutely necessary bolts on the heat shield.

On replacing the gasket, all oil leaks had ceased. The gasket was completely brittle and I noticed little notches on the housing used for guiding / keeping the gasket in place. When driven hard I immediately noticed the stumble had also ceased and has continued to do so some 3 months later. It appears the brittle gasket and these notches may have caused the engine to decompress under hard acceleration.

If you are experiencing an oil leak from the front of the engine and this stumble / hesitation on hard acceleration, it’s worth a look.

Best of Luck
Neil
 
#39 ·
2011 mini S ............

put new turbo on took car for a test drive it felt like a new car running great till I the boost of the turbo kicked in then car had a bad misfire ive replaced coil packs the misfire would go away after car sat for 20 mins or so any help ????? please
 
#39 ·
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#40 ·
Hi all,

I hope you can help me, my car has had this problem for some time. I took it to Mini Nottingham (Sytner's) and they, ahem, 'diagnosed' deteriorating spark plugs which they duly replaced under warranty. Needless to say it didn't fix the problem. The car drove a bit better but the problem came back.

Symptoms:

Under full acceleration and at highish revs the engine stutters badly causing a dramatic loss of power, this is accompanied with loud metallic pinging noises for the duration of the stutter (detonation?) and smoke from the rear. I have not determined what colour as yet because it's more noticeable it the dark when illuminated by others' lights and of course all smoke looks similar in the sodium/halogen glare!

If you back off the revs it's fine and probably won't do it again until the next day, for example. It seems to happen just once a day and the first time I boot it; usually when in second or third gear. It won't happen if I am tootling along in fourth or fifth - it's almost as if I need to take it by surprise with a sudden & quick increase in revs.

In addition to this the car and probably unrelated as this is more recent, the car's coolant has turned a murky grey/black colour - no smell of fuel or combustion gases though.

Any ideas?

Hope someone can help!!

Paul
Hi stutter on acceleration can be caused by a dirty hot film air meter (map sensor) located in the air duct past the air filter can be cleaned with white spirit and air blown dry, do it a few times you will be suprised at the result if no result may be requires changing but expensive so read about testing them there is plenty of posts on the net ggod luck worked for me
 
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