[ss67ls]

i have a 2011 x3 28i xdrive 3.0 .car runs great half the time then misses on #4 cylinder only. I had bmw replace the #4 injector and coil pack and spark plug and still does it.bmw said maybe issue with the cylinder.does not make sense it will run a day no missing then will start missing only #4 little time later miss goes away.if the cylinder was a issue it would miss all the time .any ideas

[brianhinton77]

Have you inspected the plug? Was it fouled after you replaced it?

[paranoidandroid]

Check the wiring harness going to the plug to see if there are any breaks, especially #4. You can use liquid electrical tape to fix it.

Clean all the electrical connectors and the ground terminals on the valve cover with electronic cleaner. You may need to snug up the ground terminals. Also the check the ground cable at the rear hatch.

[Barbera335]

I would pull the outer DISA flap on the intake manifold and see if it has come apart. I have a feeling you have debris floating around in the cylinder 4 intake port that is intermittently blocking the intake valve. This is a common N52 failure. I replaced my preventively just to be safe.

[ss67ls]

spark plug not fouled. i can play the switch game with plugs and coils work fine in all other cylinders exept #4,i will check he wiring to #4 i just replaced valve cover so i know all grounds and plugs are tight and good.i will check ground by rear latch.i just had the intake off replacing the starter no pieces fell out no rattles i did clean all the runners there was oil in the intake .would the disa valve cause random misfire sometimes just on cyl 4.thank you for the ideas will check any other ideas please let me know thank you

[paranoidandroid]

I had a similar issue and finally chased it down to a failed transistor in the DME - in my case the spark plug looked too clean and the misfire was constant, not intermittent like yours. I had to send replace the DME with a cloned one.

The intermittent part could be a failing transistor. This was a common issue on the E series, in particular the MSD80 DME.

[ss67ls]

thank you paranoidandroid .yes my plug looks good if you dont mind me asking how did you chase it down and who did you use for the clone dme.im thinking its the dme also was going to test light + side of coil and injector #4 and see if i lose signal to one to try and confirm dme since both are direct dme signals

[paranoidandroid]

My misfire was constant, even after replacing coil packs, plugs, cleaning injectors , and checking all the grounds and the wire harness. Compression in the cylinder was good too. I could not get the cylinder to fire at all. Ran all ISTA diags as well.

My mechanic confirmed it was definitely the DME. The guy I used to clone i found on ebay. Look at the seller premier.75.

You can also send it out to the ECU PRO (https://the-ecu-pro.com) of you don't have a local mechanic you trust. They can try repairing it first. Mine was completely shot though. It was making loud sounds too.

[ss67ls]

thank you very much paranoidandroid .I will post repair as soon as i figure it out