Hi, Wifes R56 base automatic, she says while driving on freeway she experiences a loss of power and even with pedal to the floor can only maintain about 50 mph. Pressing sport mode does not help. Has happened a few times, initially I was skeptical and thought perhaps she accidentally hit the paddle and forced into M6 mode but she says no and actually its a somewhat dangerous situation. She says engine is not shaking like it would with a spark plug coil failure (has happened before) Previous occurrence there were no codes stored but has happened again so will check when she gets home.

I did a google search "R56 loss of power" and found an old thread on Reddit describing this exactly - press accel to the floor and even downshift but still cannot maintain speed. Says he pulls over and shuts off car and restarts and problem is gone. With my wife problem seems to resolve itself after a while. Its odd that this would not store a code, you would think engine would be run very lean in this situation unless... This car is electronic throttle so its possible CPU could be ignoring pedal and not operating the throttle butterfly as it should for some reason- just a wild guess. ECU will only do this in a wheel slip situation AFIK in which case the traction control dash light would flash.

One responder to the thread said he replaced VANOS solenoids (I did that a few years ago due to cam code) and the vacuum pump which resolved the issue although it was not clear he had exactly same symptoms.
I changed the PVC diaphragm with an aftermarket when doing the timing chain replace about a year ago (I think I broke the OEM). I would think a serious vacuum leak would confuse the ECU (because leak bypasses MAF) and result in a code.

Appreciate any ideas.

 

I suspect the coil packs, I had a similar issue when I got my countryman and it was the ignition coils. They can fire intermittently so you wouldnt assume a regular misfire like a spark plug. Use a code reader and see what codes popped up first.

 

I agree symptom is similar in that engine power is drastically reduced but even intermittent coil pack failures throw codes for me and when one completely fails I get the red engine check because its a risk for catalytic damage.

Again no codes stored this occurrence so very strange.

So the guy on reddit with identical symptoms responded to me and told me it was an ECU failure. He says his shop diagnosed it - it was throwing throttle body failure codes but that had been replaced already so shop concluded it was ECU. Probably some failure of the throttle body control signal. I'll pull connector and spray some contact cleaner on it. Also I did a few drain and refills of the auto trans and every time I spilled oil on the ECU so it may have compromised the connector - I have seen this before on my truck where a connector always had oil dripping on it and eventually there was signal failure.

Dont want to bash mini too much but first repair on this car was the thermostat housing at 60k miles. As I pulled of one the connectors I ended up with lots of little shards of plastic in my hand and I saw that even though the conn housing separated all of the male contacts were stuck in the female side. Could not believe it. Was able to reassemble it but suffice to say Mini conns might not be the best in industry.

In many shop manuals it will tell you if ECU is suspected to install a known good unit but of course not many of us have one laying around.

I'll just see what happens, often these issues get worse over time and make the diagnosis easier. Over my lifetime I have had a few of these intermittent issues that no mechanic would touch. In every case that I can recall it ended up being an electronics failure of a module, sensor or in one case an oxidized relay contact.

 

As mentioned, the first step is to pull the DME fault codes.

 

Already said twice no codes but I know I'm a bit long winded so easy to miss. I have thought about this and for some reason ECU is limiting engine power.
If ECU was not intentionally limiting engine power there would be a code because of discrepancy between pedal position and throttle butterfly since there is feedback on butterfly position (safety issue).
ECU will limit power when there is loss of traction and some cars limit power during breakin, various forms of abuse, hi temp etc.

I'll clean the MAF since I have seen this cause problems on cars w/o causing a code - ECU thinks air intake is less than actual so reduces fuel although this will create a lean condition which you would think would generate a code.

Update - Just noticed I did not latch the EGR vac hose last time I worked on the car so it was a bit loose.
The EGR is spotless so did not spray any cleaner on it.

 

Fixed?

 

Issue only occurred a few times over the last few months so we will see.

Thanks for asking.

 

Sounds like a good fit. Good luck!