Low Torque and rattling

[metellica]

I have a 2004 Mini Cooper, R50. I bought it second hand and it was pretty clean and smoothly running.

Nowadays, my Mini is not capable of producing enough torque when acceleration is needed. When I apply the gas mildly, the car's response is OK. But, when I step on it, it does not produce enough torque to accelerate and rattles for 3-4 seconds and it does not accelerate swiftly, compared to its past performance. Yet interestingly, this problem does only appear when the engine reaches its operational temperature. The car's response to throttle is very well when the engine is cold.

I encounter this problem since I had the head valve cover and gasket replaced by my mechanic. I had to have those changed, since the coolant fluid almost always boiled up and splashed through the little hole on the coolant container. Changing the gasket and head valve cover resolved this coolant boiling problem, but resulted in this low throttle performance problem when the engine is hot.

I and my mechanic are trying to figure out the root problem. I have done extensive search on the Internet and Mini Maintenance Manual and tried many things. I hope that it does not go somewhere scary.

What we have done to resolve the problem: We first checked whether there is a vacuum problem on the way to the MAP (Manifold Air Pressure) sensor. We checked whether there is loss of vacuum indicating that there is a hole and we observed that there is no vacuum problem. We changed the MAP sensor, but nope, no improvement. We checked all around the valve head and the gasket, but nothing... No cracks, no leaks. Yet, there is no fault recorded by the MCU. The firing timings seem appropriate when we connect it to the maintenance computer.

Next steps ahead: We will try to replace the Crank Shaft sensor first. If that does not work out, we will have to proceed with replacing the gasket and the head valve again.

The strange thing is that; the problem appears when the engine temperature raises to its normal level. Just after car start, there is no problem with the throttle response. So, I ask to myself; what changes when the engine gets hot and finally causes these problems? Is it the gasket that deteriorates when it gets hotter? Or something else?

Any help/comment will be very much appreciated. I love my Mini so much and I would do anything to see it perform well again, cause driving it is such a pleasure.

[stead34]

I wouldn't go changing things just on a hunch its just wasted money if its not the problem. You dont say what engine you have..if the problem can be reproduced when its being diagnosed then it shouldnt be to hard to find if your mechanic is good at diagnostics, not all are..go back to basics, compression, valve timing. If there is a problem the vacuum gauge will see it you just need to know all the tests to carry out with it. If your car idles ok then the gauge will show a good reading at idle. Reading the map sensor reading in parameters whilst driving would be more usefull.

What changes from cold to hot

Lambda goes from open loop to closed loop

Injection duration reduces

Metal components expand and can alter compression, valves and pistons...

My money would be on valve timing, whether it being slightly out on the belt(chain) or variable valve timing sytem being faulty if fitted. This may show up more when cold as it runs rich when cold and can disguise this, not sure why a map sensor would operate differently from hot to cold, crank sensor I think is just a guess as I cant see any logic in that either.

Carry out a compression test when cold and hot.

Best advise though is use a different garage and send them a bill if it is related to there work. Somewhere with a rolling road would be ideal..

[dsakko]

That model never had variable valve timing (one less complication ) but yeah timing could be the thing.

I'd say if there's no fault code in the computer go through the usual mechanicy things ie check your plugs are tight and the leads / coil are ok. Check that there's no water leaking into the oil. And take your mechanic for a drive - if its a misfire they'll know the sound and helps to trace further.

And for the record it's a common thing on them for the coolant to bubble over - almost always caused by the radiator cap No need to go changing gaskets etc. Very rare for the head gasket to go in them.

[metellica]

Finally found the problem. It was caused by a very dirty gas filter.

When we were checking all our options to find the cause of malfunction, we removed the back seat and opened up the gas pump. We opened up the gas pump and we have seen that the filter is so dirty that it almost blocked the gas flow. When we replaced it, it was like a kaiser.

Now the car's performance is not sluggish anymore, it accelerates like a bullet.

Stead34, dsakko, thanks for the suggestions & guidance.