Help troubleshooting misfire please!
 

Hi all,

The misfire in my '07 3.0si has returned. When I bought the vehicle a little over a year ago, it had a slight miss really only noticeable when at idle. It was basically just a little blip/dip in the rpms. On the advice of this group I started by cleaning my vanos solenoids and ultimately wound up replacing them. Unfortunately this didn't cure the problem. Next I replaced my plugs with some NGK ILZFR6D11's and alas! the problem went away.

Fast forward to a few weeks ago and the misfire is back. I pulled the plugs to inspect them and they looked alright. I gave them a quick cleaning (lightly hit the points with some fine grit sandpaper) and reinstalled. The problem seemed to go away, only to return a day later. Since then it has only got worse. I found it strange that I'm not getting any new codes, only the same old P0420 & P0430 that have been there since I bought the truck (I have a set of non foulers I have yet to install in hopes of getting rid of those codes).

The fact pulling, cleaning and reinstalling the plugs seemed to help temporarily has me suspicious of the plugs but before I go buying another set or start looking at replacing other parts like coils, or injectors, I thought I'd see if any of you had any suggestions or ideas on how to isolate the issue

Your input would be greatly appreciated.

Thanks in advance,

Cedric

Do you have a scanner that can read the fuel trim data stream for each cylinder? If so, the readings may isolate a specific cylinder that may have a problem. Could be as simple as needing a new ignition coil.

Thanks Unicorn. Unfortunately my el cheapo reader does not pull fuel trim data. Guess it's time to invest in a better reader...

Any recommendations? Preferably a reader that will give me that fuel trim info without breaking the bank...

I personally use an Autophix ES910 scan tool. Lets me see live data streams, program batteries, etc. It was about $100. There are several options. I hear a lot of people using the more popular Foxwell tool or Carly. I think most people will tell you to get a BMW specific scanner before you throw parts at it. I have saved hundreds if not thousands of $ by using a BMW specific scan tool. If you use them correctly you can diagnose misfires before they throw a CEL. Not sure if it is on xoutpost, but bimmerfest has an excellent thread on how to use fuel trims to diagnose engine problems. I had a small misfire in mine that did not throw a CEL and this is how I was able to isolate the problem.

Amazing. Thank you so much for the info.