Hello, I have an 03 Deville DHS. Nearly 200k miles. My exhaust pipes are heavly coating in carbon. I also, have a smell that seems to be coming from only on the driver side. I had the problem before I replace my CAT, and still have it. No codes are present. Last two codes were P0303 and one about the MAF. Any ideas?

 

probably running rich, burning oil, or a spark plug is not firing .. that be my top three suspects.
with no codes and engine running "OK", i would suspect the 1st and its cause being a sensor.
1st on my list would be the engine temp sensor.

wait ..

smell from right side of what? right side exhaust pipe?
if that is what you mean, forget the sensor, I be looking at 2 or 3 as it applies to the cylinders of that pipe.


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Thanks for responding. The smell is coming from the left side near the rear wheel. I can see how the sensor will be a likely problem. The engine running in a closed loop.