I have an 02 c320. When I start it and start driving my check engine light starts to flash and then my car idles very badly and it hardly goes. The computer says the first time it was my cylinders so I changed all thw coil packs and the plugs and plug wires. And it will say mass air flow so I changed that out. And everytime I put it on computer ia says different stuff. Now I put it on computer it says bad 02 sensor. So I change that out and its still not fixed it also doesnt wanna chamge gears when it starts messing up and I hace to come off the gas to get it to. Change. I have to pull over to as well so I can restart my car...please help me

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Profile picture for user MercedesMedic

Hi!

Sorry to hear about your issues. There is a couple of things going on here.

First, the car has gone into limp mode. In other words it is stuck in second gear to prevent you from driving further and causing unnecessary damage. I would not worry about th no shift condition. The car may go out of limp mode once you fix the missfire. If it doesn't go out of limp on its own, you can use a scanner that read and clear MB transsmision codes to reset the transmission.

Second, the misfire issue. Misfires happened most commonly because fuel is not getting burned. Now there could be other issues as well. It could be a low fuel issue or a clogged catalytic converter. Or maybe even a bad head gasket.

A bad oxygen sensor should not cause the car to missfire. So I don't think that is the problem. It is more lighlty that it is a clogget cataltyic converter. What you can do is either temporarily unplug the upstream O2 sensor and see if the car runs better. Or do a back pressure test. That will tell you if the cat is clogged.

Then do a fuel pressure test and compresson test as well. These are test that you can perform yourself if you have the right gauges. Fuel pressure test takes 15 min. Compresson test takes about 1 hour.

I don't want you to keep replacing parts. Read the codes and let us know what they are. Don't erase the codes hopping it will fix the problem. You or your mechanic needs all the codes stored in the ECU. Erasing them makes it harder to diagnose the problem.

Let us know what codes are present and we can go from there.

Profile picture for user ashleybills

Ok I will get back with you on the codes in a bit.. I have heard my catalytic converter make sounds like it is backfiring and I get a stinky smell coming thru my car smells jus like exhaust. But no rotten egg smell.. But with my catalytic converter stopped up would that make the scanner read them codes to my cylinders 4 5 and 6..and what do I do with the catalytic converter if it is stopped up.

Profile picture for user ashleybills

Idk how to do any of them test your talking about fuel pressure thing I don't have gauges. And what oxygen sensor would I unplug in the upstream do I unplug them on both sides of the upstream or what?? I'm so lost with this mercedes and it has cost me so much money I can't afford all this stuff...

Profile picture for user Boki

Hi!

Which o2 sensors did you replace? 

Ones between the engine and catalytic converters (upstream 02 sensors)?

Or ones after the catalytic converters (downstream 02 sensors)?

Profile picture for user ashleybills

I did the upstream then it was bank 2 sensor 1.. So I can unhook what upstream sensor to see if it runs better do I jus unhook one or both? And if it runs better then its my converter??

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