Big Jimbo

Left Lambda frozen at 1.00. Right Lambda on a different screen with variable voltage.


For a few months my C63 with only 30k miles has had an intermittent dead cylinder and CEL that gives code P0307 for cylinder 7 misfire. It usually starts missing while driving down the freeway at about 75mph and never stops until I turn off the car and then restart it. Even if I only wait 30 seconds and restart the miss is gone for a while. I have pulled the plugs and none are fouled so I was thinking it had to be a lack of fuel, not spark. I read here several people saying that bad O2 sensors could cause the problem but have checked the O2 sensors with my hand held scanner several times (including just yesterday) and they always tested fine. Well today the misfire returned and I finally had the brilliant idea of scanning the car while it was missing before I shut it off and guess what? The Left pre-cat sensor was totally dead! There must be a German gremlin in there that causes the O2 sensor to intermittently quit working and then mess with the fuel supply to some cylinders more than others, and never throw a CEL for the O2 sensor!. I am an old guy and have been playing with FI cars for many years and have never seen anything like this. If I hadn't read about the O2 sensor issues on this site I would never have thought this possible. Thanks to everyone here for making this great information available for us crazy folks who like to search for answers and not randomly replace parts.

hachiroku

thanks for the info!

Savage-wp

Good to hear you have found the fault.