amoffitt

Hey guys,

My car seems to be losing fuel economy. I changed the air filter about a month ago and now I am thinking about change the spark plugs and wires. The car about 96K miles on it and those have never been changed since I have owned the car to my knowledge since it had 18K miles. How hard is this to do on these cars. It seems like the spark plugs are easy to access from what I saw while doing the air filters. Also is there anything else that you guys would check from a mechanical side as to why my fuel mileage took a drop? Thanks in advance.

amoffitt

Any ideas?

Trancebolt

always use premium; manual says replace plugs at 91k, dealer told me at 60!; Do the fuel filter change, run some 101 octane through it and definitely get the spark plugs changed. Any prolonged maintenance will affect you eventually.

Also, if you use tiptronic in low gear and taught the car to keep low gears, and rev higher in 2nd and 3rd, it will affect fuel economy. I used to drive my c300 to work and lightly on the streets, and got between 19-21 (23hwy).
Now, i only drive it fast in the city and get 15-19 depending on if im in any kind of drive-thru or traffic scenario. If you sit in line with the a/c on somewhere for 5 mins even, count on 1-2 mpgs to go down. Hence eco start stop being a great solution to city drivers.

amoffitt

Yea I was going to start with Spark Plugs and replace those. Do I need to replace the wires also? The wires look slightly different from anything that Ive messed with before.

babyboxer1

The spark plugs are relatively easy to replace. I followed a youtube guide just to get an idea on how to remove them. If I recall correctly, to access each spark plug, you must undo 2 bolts and pull the cap off. Regarding the wires - I've personally never seen or heard of the wires being changed on these vehicles.

amoffitt

That was kind of what I was thinking about the wires as well. They seem more advanced than regular wires but I just wanted to make sure.

amoffitt

I am thinking about ordering some spark plugs from one of the Mercedes Parts suppliers online. My question is who has experience with any of them and which ones already come with the gaps adjusted like they should be?

babyboxer1

I bought mine at NAPA, they were the OEM plugs from MB, for about $90 CND. They were pre-gapped

vipsa

This isn't a 90s benz. There are no "wires" any more. The car uses individual coil packs to ignite the spark plug. I would pull a couple of plugs and check their condition. Unless there was something really wrong with the engine at some point and it fouled out the plugs, I doubt that's your issue. Plus you would be getting random misfires.

Have you pulled the engine codes to see if there's anything stored?

amoffitt

I just ordered some new plugs so we will see if it helps once I get them put in.