1998 C230, when accelerating and especially up a hill it makes kind of a rattling/bad bearing sound which seems to come from underneath the car. An obvoius guess was pinging. And at the dealers recommendation I have tried different types and octanes of gas. After now doing this "testing" for a couple of months at least, I can say that the different octanes seem to have no effect on the noise. There is one thing in particular that makes me think it is NOT pinging and that is that the noise gets worse with higher RPM's, and seems to peak around 3K to 3500. In my experience, pinging is worse at LOWER RPM's where lugging is more likely. I can say that the noise definitely peaks and is quite bad at around 3000 RPM's. Sounds like a coffee can full of metal keys or like my refrigerator fan when the bearing goes out. Can anyone advise where I need to look for the problem? I really want this solved.

Thanks!
Mike

__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

Check for a lose exhaust heat shields. A catalytic converter that is coming apart could make that noise. Shake the catalytic converter, if you hear a rattle, its bad.

That was one of my first theories a few months ago so I got under there and shook and banged on everything. I even bent some of the heat shields that I thought might be rubbing. No effect. When I bang the side of my fist on the cat converter I just get a nice melodic tone, no rattle. I admit it does sound like that is what it is, I just can't simulate it by banging or shaking anything underneath the car.

__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

I would explore the catalytic converter further, as it seems too be the most likely cause. I would perform a hot tap test on the exhaust. Let a muffler shop do it. The catalytic converter can reach very high temperatures.

I did some more testing tonight and I am really at a loss about this problem, and I don't want to end up in a financial loss... I banged on the exhaust system while it was hot (trust me it was hot). Nothing. So then I put a mechanics stethescope on the cat and then the middle (first) muffler and revved the engine (by pushing on the accellerator with a long stick). Nothing. I am not averse to removing the exhaust system for inspection but I am not sure what definitive test I could do. The only definitive test I can think of is to put on new exhaust components and see if the problem goes away. This is a very expensive way to test! Could it be the Cat even though it absolutely passes the "pound" test? Everything about it makes me think it is NOT pinging except the fact that the noise only occurs under some load and not with any amount of revving while standing still. I am really not sure how to proceed. I can go to the dealer and throw money at the problem and sort through all their lies and mistakes for the truth. Yes, I know I am bitter. I don't know any mechanic that I trust to figure this out. Am I "overthinking" the problem. The rattling is very loud and driving me crazy. Do I just bite the bullet and buy a new Cat on a whim? That would be at least $500 and if I do that and it still rattles, well you might read about me in the paper. Any thoughts appreciated.

Mike

__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

Any competent tech should be able to distinguish between an engine ping and catalytic converter or shield rattle. There must be a shop in your area that can diagnose the cause. Let them diagnose it and you fix it. Good luck.

Did you ever solve this...I have the same issue on a 190E 1990 and its driving me mad! I changed all the exhaust and heatshields but the noise is still there!

Hello,

Yes I solved it, sort of. First I found a good test to check for "rattling cats": What you do is hit each cat with a rubber mallet. This will tell you if one is bad (It will make a rattling noise). I had one bad and one good. It was a whole assembly so I changed it. This helped quite a bit, but I thought the source of the rattling was still there and the cat was just "sympathetic" rattling. However, a couple of years down the road and it seems all the rattling is gone. I had also tested my knock sensor which was working fine.

Anyway, tap on your cats (with the car NOT running), and see if you can hear any rattling noise. What happens is the insides come apart for whatever reason.

Mike

__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra