Ml320 cel
 

Wondering if someone can review my problem and make any suggestions.

http://www.benzworld.org/forums/w163-m-class/1395439-help-what-now.html

I have a 1998 ML320 with 133K and basically I am getting a CEL with codes 300, 304, 305 and 306. I have changed the air filter, MAF and all the plugs. I have tried swapping coils and wires from side to side and still get the same codes. Each time I clear the codes and drive as soon as I put a load on the engine it knocks/pings and the CEL comes on. Thanks.

I would have the exhaust back pressure checked on the drivers side.

I had a similar thing happen with our old '98. Misfires on one side. Turned out that the cat was plugged.

check engine codes
 

Yes, the front cat disintegrates and clogs up the back cat. This is an aging problem but MAY never happen until you drive up a steep grade for miles, with lots of heat generated! My 98 ML320 was on it's way to the Pikes Peak race in 2013 with 184,000 miles on it. The loong grade between Phoenix and Payson got me, so I never got out of Arizona.

Jim in Phoenix