So I’ve got a ‘10 GL450/M273 and it’s had a little bit of a lumpy idle I’ve thought in recent history but set a CEL and P0305 cyl 5 misfire and a P0430 pending for bank 2 catalyst. I’ve owned the vehicle about 10 months and probably 15k miles. I’ve take two 500+ mile road trips with it and loved it. Smooth sailing. I have a carfax with brief history, it was always dealer maintained. Was a 3 yr lease and then the next owner bought it CPO until traded on an Alfa Romeo. That’s where I bought it. Anyhow I’m sure plugs are original but my concern is that I’m seeing my long term fuel trim at +10% on bank two, same bank as my misfire. If it’s long term positive I’m under the impression it’s actually correcting for a lean condition. So that to me says it’s not ignition related and I’m also guessing nothing like a CAT or MAF as those things all effect one full bank or whole
motor. I read an in-depth write up about a vacuum test on an E class V6 and it ended up being a broken valve spring causing the valve not to seal properly but still run decent. In that instance they specifically noted that the car had a misfire on two cylinders. They were next to each other in firing order and basically because the first cylinder wasn’t sealing 100% that it was changing how much air/fuel was available for the next cylinder. They also mentioned the extra oxygen was hard on a catalytic converter. I want to nip this in the bit before it’s a huge issue. Anybody with experience/ideas?

 

http://www.mercedesmedic.com/mercede...sfire-problem/

 

I read that. Majority of it doesn’t seem to fit. If it was a spark issue it would show long term negative not positive. Things like a MAF should effect the entire motor and some of the others would effect an entire bank. Oddly enough the light extinguished it self this evening, though it’s still of slight concern to me