W210 Poor Mileage After Cat Change

[shailey]

Hi, Folks,

The dealership in town changed out both catalytic converters on my 2002 E320 last week under warranty, (no questions asked, 79,600 miles). Since that time, my in-town fuel mileage has dropped from about 20 mpg to 10 - 11 mpg. The exhaust sounds louder under part-throttle operation. The car seems to have a harder time starting, though it runs fine after a few seconds.

I've contacted the service adviser at the dealership, but haven't heard back from him. Prior to speaking with him, I was wondering if anyone has an idea regarding the cause of the new symptoms I'm describing.

Thanks, in advance, for your help.

Steve

[Arthur Dalton]

See if they plugged the 02 sensors back in....

[ILUVMILS]

Originally Posted by shailey

.....I've contacted the service adviser at the dealership, but haven't heard back from him.....

If you don't receive a return call by the end of the next business day (at the very latest), call back. If the SA won't/can't take your call, ask to speak with the Service Manager.

One of the biggest no-no's an advisor can commit is not returning a clients' call.

[tinypanzer]

I'll bet they forgot the 02 sensors.

[nhdoc]

He didn't mention getting a Check Engine Light but I would assume not having the O2 sensors connected would trip the OBDII system and throw a code/warning light. Not that it matters, the dealership needs to fix whatever they did wrong and obviously they did something wrong.

[tinypanzer]

That's a very good point - I would expect you are correct, it should throw a code.

I guess we could sit here all day and guess the problem, but he really needs to just take it back to the dealer.

Maybe they just forgot to take the plastic cap off the sensor

[ARNOLDLewis]

First things that come to mind...
1) Correct spark plug wire routing and making sure each one is COMPLETELY pushed onto plugs and terminals at both ends
2) Correct spark plug gaps on each plug
3) Correct park plug heat range
4) Any of the new plugs get cracked during install
5) Spark plugs installed tightly
6) Maybe a vacuum line got disconnected while working in there