So I'm having one hell of an issue with my R50. At cold start vehicle runs and drives fine. Once at operating temp if I keep rpms above 1k, no issues. If I let the car at idle at operating temp for more than 1 minute, I developed a p0302 code, miss on cylinder 2. If I turn the vehicle off and let it sit for 10 mins, it runs fine. I've checked compression, I've measured cam lobes, I've traced and addressed any possible issues in wiring, and I've replaced the following.

Spark plugs
Spark plug wires
Ignition coil
Fuel injectors
Rocker arms
Valve springs
Air filter

What could I possibly be missing?!

 

Going to move you to the Stock Problems/Issues area.

That is a cylinder two misfire code. I am wondering if you have the beginning of a burnt valve. When it throws the code, try a dollar bill test (you will see a link or vid in the thread below).

 

I just went out and did the dollar bill test and I have no suction, so I don't believe it's a dead valve.

 

Provide a brief history and condition of the car, and most important the mileage. These will help a lot for others to help you.

 

3rd owner, 119k miles, r50 5spd. I don't know much about the first owner, second owner was a college age girl. I am 27 and use it as a daily gas saver. First owner did supply lowering springs and a staged clutch so I do imagine he probably ragged on it slightly, although it was in the name of a middle aged woman (maybe bought for a child or husband?) Condition wise I do have service records throughout it's lifetime and it was sold by the previous owner due to a xpin connector being corroded and she lacked the knowledge and/or finance to fix the issue. Has been a decent commuter car for me for the past year, developed the issue about 6 weeks ago.

 

I know hindsight is 20/20. I wonder why you would replace the rocker arms and valve springs, as well as measure the cam lobes?

How did the old spark plugs look before you replace them? Usually the plug in the misfiring cylinder, especially with a bad valve, would look different from the rest. I am not one to quickly jump to conclusion you have a bad valve in cylinder #2.

Did you replace the valve springs without removing the head? I ask because you would know the condition of the valves if you did, which leads me to think not. It take some skills to do this without removing the head.

In the list of stuff you already replaced, are they for all cylinders?

Doesn't seem you have given much thought to the DME engine sensors.

 

I did the rocker arms, valve springs and cam measuring after reading some forums and deciding it was a cheap measure to try and wouldn't hurt. I did replace spring but pumping air into the cylinder, compressing springs, removing retainer, replacing spring. Yes I've done on all 4. All plugs looked the same, and misfiring is only present under the conditions I have specified, it's not a constant thing. I have peeko scoped the cylinders and I did not see excessive carbon build up, but I could not see the valves. The vehicle got 02 sensors done at 90k miles, I have service records for that, and I haven't had signs of any other sensors nor any other codes that would direct me so. I have a friend that has a 02 mini, and I actually have a 03 mini that I have parted out and have the engine on a stand just in case I need to swap engines.

 

My thought leans toward one of the engine sensors since the symptom is mainly in idle/low RPM/light load. Since you have a spare engine, why not start swapping them one at a time, but always return the old one back if proven no change. It might just be running too lean at idle/low load due to a bad sensor. By bad I include being off parametrically speaking, as opposed to outright kaputt.

 

I will try swapping some sensors around tomorrow, are there any you would suggest to start with? I am also going to try swapping the ecu out and seeing where that gets me. Thanks for your assistance thus far.

 

For sensor like coolant water temp I would just compare the resistance of the two at the same temperature, instead of swapping them. They are just NTC or PTC thermistor. I would start with the easiest.

 

I would take the code pointing to specifically #2 with a big grain of salt.

 

Just thought I include not to overlook fuel delivery too, like fuel rail pressure. However reason would suggest fuel pressure/rate problem would tend to affect medium to high load.

 

I've come to terms with the cyl 2 code may not actually be cyl 2 after some reading. I have replaced the injectors, but I do not have anything to test pressure at the rail at this moment. You're going with the "low" pressure side, but I feel like it's almost flooding, since high load is unaffected and it's only at idle and clears after just a few minutes of sitting.

 

Swapped coolant temp sensors around (measured the same resistance) swapped maf/map and ecm, still facing the same issue. Here's the new question. I'm pretty sure I'm just going to either:
A. Swap entire engine
B. Swap cylinder head

A few questions, 1 what would you suggest. I have none of the special tools, nor have I pulled the head on one of these cars. 2, can you use an r53 head gasket set on an r50? Reason in asking it's much easier to find a decent quality set for an r53, and by my understanding there's really not much difference.

I'd be interested if anyone had tips for timing on this as well.

 

Modmini has allot of good Gen1 MINI vids on youtube.

 

Update:

I ran cleaners in oil, gas, and through the intake as I'm conceding to either a sticky or burnt valve. Trying the tricks before putting it down to swap the heads. As of right now, results seem to confirm sticky valves because the cleaners smoothed the issue. I will be replacing the head soon, but this will tide me over until the issue has a permanent fix, and it will allow me to upgrade the donor head before the swap. Thanks for the assistance.

 

Rather than sticky valve, I would think excess carbon deposit on the exhaust valves might worth considering. That was why I asked if, during your replacement of the valve springs, rockers did you have a chance to inspect the valves. You confirmed all was done with the head in-situ, hence no.

Carbon deposit on the back side of exhaust valve can result in glowing amber, and cause uncontrolled ignition. To this I personally has no experience to the symptom tendency - like high or low RPM. I would reason that it take some sustain high load to cause the amber glow, then immediately at low RPM the uncontrolled ignitions manifest.

I think most valve deteriorations starts with the valve guide seal harden with age, temperature, chemical attack, and mileage. Once they fails to seal well, excessive oil is sucked into the back side of the valves through the valve guides. I for one would consider replacing all the valve guide seals while the engine is relatively healthy.