Have 2007 R56 N12 (89,000 mi) throwing P0303 cyl # 3 misfire. Now, the vehicle runs great and easy to detect a misfire in a 4 banger, not the case, Performs quire well cold or hot.

I have:

Replaced plugs (due anyway)
swapped coil packs
Fuel pressure on the rail is good
Removed and tested all injectors, just fine
Compression, a little high but consistent @ 220-225 psi across all, wide open throttle, fuel pump disabled
Traced all injector and coil wiring, good.
From the somewhat high compression, looking at the piston crowns seems some carbon buildup so I tried the Seafoam thing, without any difference (compression OR performance)
no oil leaks from the plug seals, so replaced anyway to be in "good form"

so..... clearing the code results in about 10-15 miles before re-occurrence of the P0303, hot or cold start, easy or "spirited" driving.

Just stumped, since the damn thing runs so well and has been for the last 3-4K miles with this issue

Anyone seen this before?? thx.

 

Yes, take the car to an indy shop and have them put it on the scope. My problem was an intermittent injector that showed up on the scope. Replaced injector (just the #2 cylinder) and the problem disappeared.

 

Did you have a P0302?? thx.

 

Yes.

 

Yes I understand the DTc's..... P0301, cyl#1 Misfire, P0302, cyl#2 misfire.... etc...

Was Kindly asking what was YOUR DTC code? thx.

 

He does have a good idea, move the coil and injector to another cylinder and see if the code follows...

 

Nope.... coil and injector already swapped, no change still P0303

 

What do I know, just have a R53...