Hey everybody!

I have a 2007 R56 justa, with 48k miles. The car is suffering from a pretty nasty knocking sound (especially because I live on a hill!). I purchased the car a while ago from a mechanic, and he said he would fix any issues on the car.

what the mechanic has tried:
- replaced knock sensor
- replaced knock sensor harness
- replaced mass air flow sensor
- seafoam in the gas tank (twice)
- adjusted "adaptation value" (twice)

The mechanic is a bit lost now, but thinks that adjusting the adaptation value again might solve the problem. He is saying that the motor itself is good, but that the engine management system is forcing the engine to run lean (hence the knocking?).

I'm a bit skeptical, and think it might be a more fundamental issue with compression (potentially piston rings?), so I will try to check that later this week. Also, I will try to scan engine error code and post it here.

Anybody have any other ideas of things to check?

 

Disconnect the battery for 30-90 minutes. Sounds crazy I know but read here (jump to end): https://www.northamericanmotoring.co...013-justa.html

 

Ironically, I did exactly that earlier today, while I was working on something else.

Upon reconnecting, the Mini did seem exceptionally strong, with no sign of knocking.. but the knocking later returned. I will try disconnecting the battery for a bit again tomorrow to see if I can recreate the no knocking scenario.

 

What fuel are you using. Have you tried a tank of premium?

 

I have been using only premium for several months.

I just got back from reconnecting the battery after 2 hours, and driving it around. The knocking is still very much present :(. I noticed that the engine light was still present after reconnecting though, which makes me wonder whether the system was actually reset. I will try again overnight this time.

 

I just disconnected the battery for another 30 min, depressed the brake pedal a few times, and reconnected.

Upon reconnecting, the engine seems to rev really well in the low gears, but once I hit a higher gear and put the car under load, the knocking comes back, and it feels like the throttle response is reduced. This makes me think that the engine could have some inherent issue causing knocking, and the engine management system is reducing power, as a result (not the other way around). I am not sure yet whether that makes sense, but it's the current hypothesis.

Any good ideas around diagnosing this? I will try to check spark plugs, measure compression & do a leakdown test at some point, but it still seems very high level. Anything in particular I should check via a scan tool? I think I will have access to one via the local college auto shop class.

 

If you want to read error codes in the computer you can buy a cheap elm327 Bluetooth adapter and install Torque or a myriad of other ODBII apps on your phone. Plus you can use BMWhat to program hidden features if your car using the same adapter. I have no idea though about the knocking. Maybe a deeper search of this site would help.

 

Why not find a qualified mechanic?
Sounds like you, your car and your mechanic could all use one.
Is the knock pre-ignition?? Rod knock? Valve train knock?
Check intake valves if the former...., pull plugs and take a look with a scope.
Get the codes; probably misfires.

 

If I hit a dead end, then maybe I will! Investigating this myself is more fun though

Ok, I finally was able to hook up a scan tool to the car. I took pictures of the live results (attached). I did not find the freeze frames in this tool in the time I had. However, after resetting the codes, the engine light turned on again and I later scanned it with an elm327 adapter (which showed a P115C, Air Mass too low code). Below is the freeze frame info I was finally able to pull from the elm327 adapter.

Though the long term fuel trim on the freeze frame below is slightly negative, it looks like it's within acceptable range (given a basic google search). The air mass flow rate does seem a bit low, but I haven't found any good references on where that number should be around for a given speed. I suppose it can be roughly calculated given the speed of the car, but I think the air flow pressure in the engine would alter this calculation a bit.

What do you guys think would be a good next step? I could try the MAF cleaner, but not sure if the snapshots indicate I should focus elsewhere.

Freeze Frame
-P115C: ISO/SAE Reserved (Powertrain, Generic)
-Fuel system status: Fuel system 1: Closed loop (1)
-Fuel system status: Fuel system 2: NA
-Calculated engine load: 62.4 %
-Engine Coolant Temperature: 46 °C
-Short Term Fuel Trim - Bank 1: 0.0 %
-Long Term Fuel Trim - Bank 1: -3.1 %
-Engine RPM: 2793 RPM
-Vehicle Speed Sensor: 33 km/h
-Ignition Timing Advance for #1 Cylinder: 16.5
-Intake Air Temperature: 18 °C
-Air Flow Rate from Mass Flow Sensor: 29.63 g/s
-Absolute Throttle Position: 42.7 %
-Time Since Engine Start: 166 s
-Commanded Evaporative Purge: 100.0 %
-Fuel Level Input: 34.1 %
-Barometric Pressure: 100 kPa
-Control module voltage: 14.35 V
-Absolute Load Value: 67.5 %
-Fuel/Air Commanded Equivalence Ratio: 1.000
-Relative Throttle Position: 32.2 %
-Ambient Air Temperature: 14 °C
-Absolute Throttle Position B: 43.1 %
-Accelerator Pedal Position D: 40.4 %
-Accelerator Pedal Position E: 20.0 %
-Commanded Throttle Actuator Control: 42.7 %

 

If the justa's suffer from the same carbon issues then I would say that your valves are coked up.

There is a lot of threads on walnut blasting. It might be worth looking into.

 

If he's getting oil coked valves his valve seals must be letting oil through down to the valves.

 

Actually, justas don't have direct fuel injection, so they do not suffer from the same carbon valve issues as the S. This was part of the reason I opted for the base model. However, it looks like I have my fair share of issues anyway .

Thanks for the suggestions though!

 

I should say that it's possible the valve seals are an issue. Given that it's only 49k miles though.. it seems unlikely, right?

For the P115C Mass Air Flow too lean at idle code, are there a set of steps used to diagnose the MAF?

 

I too am interested in this P115c code. Ive been getting this code on and off for a few months now.

Usually when it comes on and I take some time to clean the MAF and use a scanner to clear the code (takes about 3-4 attempts at clearing).
Originally I had a custom charge pipe installed that deleted the noise maker so I thought that might be causing "too much" air to pass so I swapped for the oem pipe and I've yet to see a code (fingers crossed)

 

Woohoo! P115c code has been solved. It was due to a leaky pcv hose. Power is restored to the mini.

Now to diagnose the weird rattling sound that shows up on hills.. The shop thought it might be normal drivetrain sounds, but it seems pretty bad to be normal.

The knock sensor appears to be faulty, but will replace that later (as there is no knocking).

 

Weird rattling sound could easily be knocking... Potentially very hazardous to your engine's health!

 

hey everybody, the rattling sound has been diagnosed and fixed.

It was indeed detonation. Turns out the knock sensor itself was fine, but the engine harness had a break in it. After repairing the break in wires, the engine runs much smoother, and no detonation is taking place!

It is suspicious that an engine harness would have a break in it, given there were no accidents. I suspect that my mechanic swapped the harness with another one that had a break in it, while trying to repair one of the other issues (for free..).