CPO is a fantastic lie the industry came up with. At least you have a warranty tho.

JB+ wouldn't kill your plugs like that. Original plugs. BMW changes them every 100k.

I am willing to bet you need a carbon cleaning. I got my car at 52k, put 25 on it never had a carbon cleaning. NEVER.

 

I've been having this same problem for the past two weeks. CEL comes on almost every time once the fuel level goes below 1/4 tank. Misfires in the 4 and 6 cylinders. Decided today to do all plugs and coils since they were never done and my car is at 66k miles.

 

The BMW replacement interval for spark plugs for the N54 engine is 45k miles (usually +\- 5k).

 

Is it really? Its half as bad then.

I went to Rallye BMW with about 60k on my clock and bad injectors and they said they were going to change the plugs because they were never done and weren't due for a while.

It was then when I decided that I was taking maintenance my car.

 

I was experiencing similar issues (misfire/stumbling under acceleration) on my 08 535xi (82k), and thought for sure it was a bad injector. Brought it in, and they diagnosed it as carbon buildup on the intake. They walnut blasted the intake manifold and replaced the plugs, and the car runs like new. Carbon cleaning was covered under the 82k mile emissions warranty (?) and plugs were covered under extended maintenance. Based on the service records, it looks like they did the same thing around 42k miles. Definitely seems to be something that is required every 45-50k.

 

Normally it is 100k and so SA's will assume it is the same for our cars. However for turbo'd engines the CBS is plug replacement at 45k. I've been lucky that both SA's I use have 335i's and they know the correct service intervals BMW follows. In fact today I took it in for oil change and vehicle inspection, mentioned that I had a baby rattler under the car and my SA took it from there. Got the call that car will be ready tomorrow with new turbos, brakes, and oil changed. Now I can finish my etune and then PM wedge to do the SAT flash.

The walnut blasting was probably covered by a cpo warranty. The emissions warranty extension was only for the turbochargers due to the wastegate issue. No matter what that was great of them to get it done. My car doesn't have any symptoms so I'm just going to bit the bullet and pay for the cleaning of my intakes. Luckily it's only $350 for the cleaning.

 

You guys got good BMW SA. The ones I experience are cheap as hell until its on your dime. I got quoted a thousand for carbon build up. 200 for brake flush, and 250 for carbon filter changes. It seems like they get comprehensive once the warrantee and maintenance plan runs out.

 

And I thought mine were bad. Just changed them today. First started noticing misfire under heavy acceleration once the JB4 was fitted. After a couple weeks waiting for the parts to arrive from BMS it was starting to misfire on map 4 even. This:

 

If a plug has been misfiring for long it can take out the coil too. Coils should last if plugs are always fresh and working right.

 

is there a DIY post on changing coils & plugs?