Hi everybody,

I have a 05 clk320 cabrio. I need some advice on what to do on my car to make it run better. By better, I mean power. The car is very slow when accelerating from idle. It also seems to be idling a little rough but not terribly. It doesn't feel like it performs like a mercedes should. I have been maintaining it very well but there must be something I forgot to do. The car has 98,000 miles on it.

Things done on it:

Spark plugs -93,000 miles
A/T service-90,000
A-service at 97,000
Egr valve replaced-95,000
Belts replaced
Fuel filter replaced

There is a weird rattle coming from the rear of the car. I was told it could be a bad catalytic converter and it could be causing this. Maybe the MAF sensor? Any help would be great!

I have one more question:
How good is the m112 engine as far as reliability, and power? Are they strong engines? I'm almost afraid to drive my car at high rpms because it doesn't feel like it is a strong engine. It feels like a weak engine and I'd hate to make it work harder than it can. Am I wrong?

 

The M112 is a solid engine - one of the best MBZ has made since the M617 (the 3.0l 5-cylinder diesel from the W123). Do not hesitate to give this engine a workout - it's built for it.

In terms of HP and torque, it was great in its day (late 90's/early 2000's) but by current standards, it is probably a bit below average. Still, it should not feel sluggish unless you other car is a modern V8. Any sort of rattling in the exhaust, especially as you approach the 100K mile mark, is suspect of catalytic converter failure. Often what happens is the hot, molten platinum material breaks away and ends up lodged in the resonators and muffler, causing restrictions, definitely resulting in poor performance.

 

Would cleaning or replacing the MAF sensor help too??

 

I replaced my original MAF at 200k. There was nothing wrong with it, no codes, errors, or failures. I felt no difference with the new one.

 

If the catalytic converter happens to be clogged, does it have to be replaced or can it be cleaned out?

 

I don't believe you can unclog them. Even if you could, you would have to remove it to do so and that is probably 1/3 the cost of just replacing them. Just make sure you have someone check that they need replacing before just changing them.

They often make a rattling sound when you rev the engine in neutral or under heavy load when driving. The rattle is due to the ceramic or metallic substrate (to which the precious metals used to convert NOX is attached) having come loose at the point/s where it connects to the cat shell.

When they are just clogged, the "clogging" is likely exhaust residue blocking the perforations in the substrate. The exhaust must flow through these holes. When it is more difficult for the exhaust gases to flow the engine has to overcome the resulting back pressure. Over time, the pressure of the exhaust from the engine will break the connect points and you will start to hear the rattle. Pieces of the substrate will start to break off due to the vibration. These pieces flow to some downstream point until blocked (generally in the muffler).

 

Yep, Fat is on the mark - the cats themselves don't get clogged. What happens is the platinum in them has finally been all used up and the resulting material becomes brittle and breaks apart. Molten pieces of it lodge in the resonators and muffler. While you could just replace the cats themselves, you will still have clogged resonators and mufflers downstream. This is my MBZ only sells the exhaust as one complete "system". Its actually fairly simple to replace, except maybe dealing with a few rusted attachment bolts.

 

Is it safe to use aftermarket cats on this car? What brand do you recommend?

 

I use magnaflow but my setup is very different than stock. Even though I was able to run a wire through my stock muffler I would not recommend that as a method to clear any foreign objects. And you would still have the resonator as a possible point of clog. It would take additional cuts and welds by someone who could do quality "butt" welds and who would take the time to ensure the resonator and muffler were clear. Otherwise you have a chance that the clog would remain after the cat replacement.

This could be more costly than replacement;

re Rodney's point that Mercedes sells the whole exhaust.

 

Check engine light just came on with code po455. Maybe this is the reason for the poor performance and vibration? Idk

 

P0455 is "P2013 - [2] Major leak in purge system : Hose in system not connected or filler cap open". This likely won't affect performance. First check the fuel filler cap. If it seems secure, it may need a new gasket. Or you could have a leak in the filler neck.

 

Everyday I drive my car, it feels like it is getting worse! I know it's 10 years old and coming up on 100,000 miles but the car just doesn't drive right. It's not comfortable on the road because it doesn't feel as smooth and the car seems to want steer itself ( if that makes sense). Also, the power it has is just awful! It feels like it's got no guts. Takes forever to get up to speed in the damn thing. Almost like this heavy car is way underpowered. Believe it or not I get a better joy out of driving my moms 2000 ml430 than driving this. It feels smoother, and also shifts on the dime. My clk just isn't comfortable at all. What should I do to make it feel like a Mercedes again???

 

At that mileage, I'd expect the suspension to be shot. The "upper" control arms have fluid-filled bushings that rarely last more than 50K miles. The performance issues could be the catalytic converters reaching end-of-life.