trivium91

Hi Guys, i have a 2005 C230 and the check engine light came on with a misfire on cylinder 1 and 4...its actually the wifes car so she wouldn't know even if there was a misfire until the engine stopped working all together. When i test drove it everything was fine, so i restet the check engine light and it hasn't come back on since...although i imagine it will eventually come back. At any rate the other codes that came up with are relating to the O2 sensor/s and the cat. Im bought new ignition coils and im waiting for those to arrive since for reliability those likely need to be changed anyways, however I imagine at 120,000 miles the cat converter is likely getting or soon to be clogged. Im in canada where there is not any catalytic converter laws, if i cut it out i imagine the check engine light would be permanently on...im fine with that. Would it affect mileage or timing or anything else in the engine? I have a budy that removed his on a newer VW golf and everything was fine other than the check engine light.

slammer111

Cats generally don't clog over the lifetime of a vehicle unless you've been running with emissions problems for an extended period.

If your ignition coils have gone bad, then unburnt fuel could dump into the cat, which may ruin it. However if there is such a misfire, there is no way anyone driving the car wouldn't know instantly. This car shakes like crazy (worse than a lawnmower) below 3k RPM when a cylinder craps out. Also I assume the car is smart enough to cut the fuel to the cylinder when the misfire is detected so as to not ruin the cat. If you had 2 of them fail, then I imagine the car couldn't even idle.

Personally I would replace both ignition coils and clear the codes, then keep an eye on the car before doing anything drastic. At this point your O2 sensors might not be bad. The O2 sensor codes may be caused by the failed coils upstream.

The ignition coils either fail intermittently (works fine until I floor it; restarting the car makes it work again) or crap out completely (restarting the car does not fix the problem).

The ignition coils have a recommended replacement interval of 160k km. Personally I just kept spares around and replaced each one as they died. The first one for me died at 197k, which is basically where you are in terms of mileage. Right now I'm at 234k and 3 of the 4 have been replaced.

I imagine removing the cat is going to make the car throw off the fuel/air mixture upstream. Might kill your mileage but this is just a guess.

Russell Ormerod

Rather leave the cats alone. Only workshops that have little knowledge advise to remove them.

trivium91

Hmm im used to old vehicles i guess where the cats clog easily. I build old school mopar stuff though, just finished the top end kit in a 360 5.9L with aluminum heads, 0.525" lift Comp Cam so i would agree that when a cylinder isn't firing you will definitely feel it especially in a 4 cylinder. Im thinking it was just a split second where it failed and the wife never noticed it, or perhaps on startup it glitched and tripped the CEL without her noticing. At any rate, i have four new ignition coils coming and i will monitor it. The upstream O2 sensor most definitely monitors the air to fuel...i guess the main question is than what does the downstream one do? Theoretically the downstream would monitor the conditions of the cat and throw the code when its not within spec, so perhaps it does nothing more than that. Has anyone actually removed their cat though? What about the O2 spaces that are supposed to trick the sensor?

slammer111

You are correct, the downstream O2 sensor is there to ensure the cat is working properly. No idea what the readings would be but I'm guessing the cat helps to burn up some of the particulates, which would lower the O2 level downstream.

If I were to guess, your ignition coils or spark plugs are on the way out. I would look into changing all 4 sparks too (or 1 at a time based on which cylinder is malfunctioning, your choice). Personally I've never had the sparks fail. It has always been the ignition coil which caused the CEL.

Most ignition coils fail under load. Every one of my failures occurred while I was heavy on the throttle, usually when I was on a highway on-ramp. It was very predictable.

I've been told that cats on modern fuel injected engines basically last forever unless the engine was malfunctioning (ie spewing raw gas or oil or coolant into the exhaust stream) and the problem was ignored over an extended period of time, leading to the cat either overheating and burning up, or getting coated with something that stops the chemical reaction from happening. In fact I'm not sure if any W203 members here ever had a cat that went bad due to a manufacturing defect.

trivium91

Very true, a misfire could cause the sensors/cat to read something outside the range for a second or two. Perhaps thats all it was than, stil waiting on those ignition coils. I wont be removing the CAT at all unless i know for a fact that its clogged. so for now im leaving it in there and changing all the ignition coils when they arrive.