nickclk430

to make a long story as short as possible I picked up a 1999 CLK430 and had the MB dealer do the inspection everything came back fine. The car had the mass air sensor replaced about 4 months ago by the same dealer for the previous owner. About a week or two after I purchased it I noticed that when I punch the gas real hard the car was basically falling on its face and accelerating real slow with the RPM's at about 3500 rising very slowly. I took it to the a different MB dealer (where I live) and I had them service the tranny to be safe. It still ran bad when hitting the gas hard so I took it back again to the same dealer they ran some more test rest the adoptions and said the only thing that came back with any problems was the crankshaft positions sensor instead of paying another $300 to have them do it, I ordered it and replaced it myself a couple weeks later but since they had re-set everything it ran great for a week in between. Before I replaced the CPS I did a battery reset at my house instead of going back to the dealer and that fixed it for another week or so. Right before I actually did replace the CPS it started doing the same thing again. This time I took the car to a very well know independent MB mechanic called MBI here in Portland OR. They did all the test they could said all the adaptions where almost perfect but did say that the CPS had not been reset since I did it myself. They cleared the ME (Engine Electronic Control Module) to the initial factory settings. And of course the car runs perfect again. They said that if the problem comes back then they are pointing to-wards a new computer. They said I could get a used one and send it to Beckman Technologies in N. Carolina and they could unlock it for me. I called them and spoke to a gentlemen and he really doesn't think I have a bad computer he said these computers are always mis-diagnosed and they are a very reliable computer. So right now I'm stuck and really hoping the problem doesn't come back and something MBI did get fixed but if someone has any ideas as to what the problem could be please please help me out here. Oh yeah car runs perfect all the time if you don't punch the gas, I only know there is a problem when I step on it.
Thanks so much

MarcusF

I'd check the catalytic converters. The center substrate is known for breaking loose from the outer shell. When that happens, the ceramic material can rattle around until it breaks and partially blocks the exhaust. This can be checked by removing the primary O2 sensor, running a borescope down the hole, and visually checking the cat. Alternatively, checking the exhaust pressure at the primary O2 sensor on both sides will work. Check it first at idle, then at 3500 RPM. If one side has a lot more pressure than the other, I'd guess one of the cat’s on the high side is bad.

IHTH

CurYousGee

Dang Marcus, I have been on the forum for years, and you always have tons of knowledge....

MarcusF

Sorry for the delay in thanking you for the complement. I didn't subscribe to this thread, and I thought I did. Anyway, some of the answers I've had are from stuff I've done before, or when I've helped someone out on a project, or researched an article, read about, or worked on something related.

So Nick, was that it? Because if it isn't a bad cat, I'd really like to know what it is. If the ECU / ME has a fault, it would be interesting to find out why. Wet, hairline crack in a board, bad solder, voltage issues, it's got to be something. Please post back when you find out. Thanks.

nickclk430

as of right now the car still runs great since they cleared in on Monday, I'm praying it keeps running good and maybe the kink got worked out. I'm leaning to something besides the computer. The old tech who use to work on it thinks it might be a EGR valve?? I called him this week and explained the problem. I'm also leaning towards a bad mass air sensor the one he might have put in 6 months ago might have been faulty. I will keep you updated on how it goes and thanks again for your help, you really do know a lot about these cars