E320 Wagon Losing Power, Making Strange Sound
 

My parents have a 1994 E320 wagon that has been causing some trouble lately. The "check engine" light came on recently, and our mechanic diagnosed a bad O2 sensor. While he was working on that, he noticed that some of the cylinders weren't always firing. He found that the insulation on the wiring harness was bad and there were bare wires in places that were causing a short. So that was replaced, too.

The car still drives like crap, though. I have a 560SEL and a 400E, and they are both pretty quiet, smooth, and fast. This E320 wagon is totally different. When I press the gas, I can hear a metallic scraping-like sound in addition to the engine sound (the sound comes from the outside, not from inside the cabin). Very hard to describe it -- kinda like the OLD VW beetle's engine, but raspier and more metallic, superimposed on TOP of the benz's normal engine sound. It only happens when I press the throttle -- as soon as I let up on the gas, the sound disappears. It also isn't present at idle, not even if I press the gas with the car in "park". Only when I'm in "drive" and pressing the gas, especially when I press it harder. And the car feels really weak. I have little to compare it to, since my other benzes are V-8s, but it feels too weak for a 217hp engine. At times, it can bolt. But at other times, it feels like the old Camry wagon my parents used to have, and it seems to hesitate before accelerating.

Thanks for reading this far. My parents are trying to decide between further repairs (they've already shelled out over $2K on the car in the past month or so) or tossing the car. The body is in great shape, and it only has 100K miles on it, so I'm thinking there should be plenty of life left in it, but I agree that it sucks the way it is now. Ideas on what could be wrong with it?

Thanks for all your help!

Take it back and ask the shop to see whats wrong. Don't ask them what they did wrong.

They should deal with the diagnosis with an appropriate point of view if you don't come at them aggressively.

With that said don't allow much of what they find to be your problem. If they are fair they will probably unerwrite much of their diagnostics costs even if there is another problem.

Remember from their point of view the current problem is no easier than the first problem (maybe a whole lot harder).

Your description rings no bells in my head but from a lot of experience I would replace the sparkplug connectors under the three coils. They often cause load related misfiring.

Reading your description of the sound gave me the impression you may have an exhaust leak. The would be from the exhaust itself or from the egr system.