ok ill try to keep it basic 151k, 04 S, 15% pulley, screamin demon coil, 1 step colder NGK iridiums, alta cold air intake, RMS tune(done last september), no issues for @25-30k or until 2 weeks ago!
get cyclinder#2 misfire code, change plugs, wires, coil, ...drive....code on again, switched #2 and #4 injector, reset code, drive ...on again!! took to mechanic, he did compression and bleed down test on cylinders, said all was resonable, he did not give me hard numbers, but my own compression test ran between 138 t0 150, nothing crazy, he said he thinks problem was o-ring on #3 injector causing vacuum leak, replace it(which i think i damaged previous day) reset code, drove...on agian! bought new plugs, stock ngk replacements, drove, SES light back on, switch coil and wires again, same thing, rough idle, at highway speeds no issues, gettin real close to 30 mpg!
also now, it will start to idle real rough, can tell its missing, then the SES light starts flashing, rev it up alittle, flashing stops...still rough idle
did a fuel pressure test at rail, ignition on right at 50 psi, start it, drops to 45 psi, 2k its drops down to 40 psi, not sure if thats acceptable, the 50 at ignition is good, not sure if it should drop at higher rpms that much?
but on a good not, i put around 145k on the car myself, always exxon/chevron 93 octane, change oil 3-5k, no major issues in last 5 years until i get these gremlins! any help would be apreciated, cant afford to jus throw money and time at it right now, maybe later! its the old needle in a haystack, and i cant have a shop guessing at it for days, dont like expensive needles! thanks

 

I am not liking the fuel pressure numbers at all......wonder if your fuel pump is having issues.

BTW: Have you ever changed the fuel filter ?

 

thought fuel pressure was supposed to be 50 psi spec, changed fuel filter with in the last 10k

 

Try running half a can of seafoam through a vacuum line into the intake and see if that makes a difference. Otherwise at this point I'd be pulling the supercharger/manifold and having a look at the backs of the valves.

 

First thing I would do is a compression test and you've done that. Second thing is that I would look for a vacuum leak. Maybe intake manifold gasket? Vacuum leak symptoms sometimes go away when you raise the rpm off of idle. Just a thought. Vacuum leaks will throw off the fuel mixture and make for a rough idle.

Hope you find it

Bob

 

Dropping down to 40 at 2K RPM's seems low.

My thoughts were:
51-52 at pos 2
41-42 at idle
61-62 at Rev.

 

151k is a good run....depending on how it is running, it could even be more of a cam/spring/rocker issue, or even a head issue. It seems like you have beaten the simple stuff to death...
My suggestion...if you have a way (like a flash tool) remove the more agressive RMW tune, and put the factory tune back on the computer...see how it runs....if it runs ok, then a sudden change in your motors condition (drop in compression, carbon build up, maybe a hotspot on the head) has made the custome tune too agressive for the motors condition, and once corrected, you can reflash the old custom tune, and be in good shape.
One question on your train of thought...if the fuel preassure was too low, why would it be one cylindar, consistantly be misfiring....you already moveed the injectors around, elimnating that it could have a slightly clogged injector (which would have been exasterbated by low fuel preassure).
After moving the injector, the problem remained...on the same cylinder... in my head this points you toward a mechanical issue, or sudden change....

 

This situation happened to my car 5 months ago. Dealer told me I need to overhaul my engine. I did all the test and all came normal. I replaced the brand new spark plugs with a new set of NGK 4 prong plugs. Everything just went back to normal. Try it.

 

 

Pass the popcorn...

 

1 1/2 cans of seafoam through vacuum hose, 1/2 can in 1/2 tank of gas, put around 80 miles on it, no change same code, #2 misfire,
the plugs which i put on yesterday where brand new ngk 4 prong, switched back to the old iridiums for the seafoam treatment!
new idea... IF some oil came off my air filter, what would that do to the system?, got some MAF cleaner im fixxin to spray through it and then put new plugs back in, and drive!!!

 

A dirty sensor would likely result in generaly poor running on all cylinders...as the air is fead past it to all of them. Over-oiling a reusable air filter can cause some issues, but the codes would not be so specfic...#2 misfire is very specfic....
And please remember, sea-foam is good stuff, but adding it to your fuel will, like most petrolum based cleaners, drop your octane a bit, possibly causeing more of an issue. I would go in the opposite direction...drop a can of octane boost in...and see if adding octane helps. But remember, it is looking like a mechanical fix is needed....delaying, and trying to use a "mechanic in a bottle or some majic oil" will likely be a waste of time and money, and they my cause, or allow more dammage to occur.....

 

Went through the same sort of thing a few weeks ago. Cylinder 1 and 4 misfires and P0300 non specific cylinder misfires. I replaced coils, plugs, wires and fuel pumps to no avail. Finally had two different shops look at it in the Charlotte NC area. Turned out to be the engine temp sensor. My spec is way different than yours, my 2006 S is almost stock and has 84000. Might be a shot in the dark, but it might be something to check.

 

1st-gen MINIs don't have a Mass Airflow Sensor (MAF). They use speed-density, which requires two Manifold Absolute Pressure (MAP) sensors. One goes to the engine, the other vents to the atmosphere. Computer reads between these, as well as accelerator actuator, O2 sensors, etc., to determine proper A/F ratio.

If you read through the forum threads, you will see some have had issues with the Screamin' Demon coil pack in the past. Did you put the stock coil back in or buy another Demon?

If you bought the remote tune tool for uploading tune files from Jan, +1 to try the stock tune. If Jan tuned it directly, that's not gonna be possible.

I'm guessing you checked the fuel pressure at the end of the rail. What about checking the fuel pressure regulator valve itself?

Can you recall anything out of the ordinary around the time the problem started? Did this start after a really hard acceleration, or perhaps while driving at 3K RPMs on the highway for awhile?

+1 to Gray Raven's comment on the fuel pump. I don't have a Bentley Manual in front of me, but researching through the forum, you should have no less than 50 PSI +-3.