rattling noise when hit accelerator at low speeds
 

I recently purchased a 2001 slk320 with 29K miles. Car has been fine, but about 2 months after purchased I noticed a strange rattling/pinging noise coming from the engine when I accelerate at start-up. I am not sure if it is coming from the engine or the exhaust. If I have the car in park and hit the accelerator, the noise is most noticable after I let up on the accelerator and let the car go back to idle. It sounds like metal rattling on metal. I am a novice when it comes to servicing my MB, so please be gentle.

RE: rattling noise when hit accelerator at low speeds
 

Need to get car on ramp.
Check if exhaust heat shields are touching exhaust. If not check if noise is coming from catalysts near gearbox. If so this is a common problem and is especially noticeable when cold. Unfortunately replacement catalysts are expensive.

If it is the cats let us know and I will give you a low cost alternative way of resolving the problem should you be interested.

Stuart

RE: rattling noise when hit accelerator at low speeds
 

sdufour if I may ask, how much did you pay for you 2001 with 29K on it. I am selling my 2001 with 35K and want to get a good starting price

RE: rattling noise when hit accelerator at low speeds
 

Thanks for the information....I am almost certain it is the cat, which the dealer said they would replace for free under the 8month/80K mile warranty. I will take it in next week and let you know.

In regards to the earlier question regarding price, I paid $23,000 in Feb of 2006 and the car had 28,000 miles at that time. I thought that I got a real good deal as it was a single owner with all the records and a clean bill of health from the MB dealership. It still had the original tires(which will need replaced shortly) and a bit of curb rash on 2 rims. Otherwise in execellent condition. I purchased it from an individual and believe that I got a good deal. I found other 2001 SLK320's that I was able to get for just shy of $24,000 from independent dealers(who knows where the cars came from), but the mileage on those were about 40,000 miles. I hope this helps.

RE: rattling noise when hit accelerator at low speeds
 

Also the cats can touch each other and rattle before they get real hot and expand.
This makes a similar noise to a broken cat.

Bazzle

RE: rattling noise when hit accelerator at low speeds
 

I hope the garage honours its committment under the warranty.
Stuart

RE: rattling noise when hit accelerator at low speeds
 

Dealer fixed the cat converter for free under the extended emissions worry. Thanks to everyone for their help. Can't believe I am leaving the dealership witha a $0 invoice.

RE: rattling noise when hit accelerator at low speeds
 

What, pray tell, is that low-cost way of resolving the problem?

RE: rattling noise when hit accelerator at low speeds
 

Hi,

Glad you got OE parts fitted at zero cost. Maybe you could get my dealer to do the same!
MB UK aren't interested. They know there is a problem but if the cat is over 1 year (possibly 2 years under goodwill) they won't play. You guys in the States don't know what we have to put up with over here.

UK Spec 320's are fitted with California tuned engines presumably in order to reduce the number of engine variants on a low volume derivative. Dependent upon where you live this could be different but I suspect not.

Since the vehicle meets Californian emmission regulations this means that the vehicle is cleaner than it needs to be to meet UK (and potentially other countries) emmission requirements.
In addition the UK 3 yr MOT test does not require the vehicle to meet original equipment levels of emmission, just an arbitary lower standard. You don't need 4 off, 3-way, Closed loop cats with air injection to achieve this arbitary level.

The solution is to remove the bricks from the intermediate catalysts (these are the ones that rattle when cold). Easily done and the casing design is such that once "repaired" you need an expert eye to tell that the can has been opened.

OK, this procedure will alter the back pressure on the system slightly and this may impact the tune map. My personal experience is that it made no difference other than to make the mpg slightly better (measured over a 3000 mile measurement period).
It also makes the exhaust note a little more "delicious"!

Replacement cats, (MB fitted) are circa £1000 here in the UK. Outrageous! Unfortunately nobody manufacturers a bespoke aftermarket cat system for the 320 SLK except specialist tuning firms who also take advantage of the reduced cat requirement.

Stuart

RE: rattling noise when hit accelerator at low speeds
 

AH, I wonder what would happen if I replaced the cats with resonators. Would the change in back pressure screw up the power?