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Michael Warfield
Michael Warfield, Factory Mercedes-Benz Technician
Category: Mercedes
Satisfied Customers: 3131
Experience:  Mercedes-Benz Master Certified technician
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I have a Mercedes ML320 1999 Codes: P0300-080 As well as O2

Customer Question

Hi, I have a Mercedes ML320 1999
Codes: P0300-080
As well as O2 sensors codes and misfiring on cylinders 3,5,6 Damages TWC
other codes i got: P0300-067,
Please help!
Thanks a lot!
Submitted: 1 year ago.
Category: Mercedes
Expert:  Michael Warfield replied 1 year ago.

Have you done anything to try and repair it? If the misfires are located on both banks 3,5,and 6 and not just one bank 4,5,6 or 1,2,3, then I would suggest replacing the mass air flow sensor with Bosch branded one only. It would be better if you could just swap one from another V6 mercedes for testing, anywhere from 1998-2005 should work. If that doesn't work, then I suggest checking your spark plugs and check the spark plug wires for corrosion. Sometimes water or oil gets in from the valve cover gaskets causing misfires. My next solution would be to disconnect the catalytic converter pipes at the exhaust manifold. Each pipe has two 13mm bolts and I would just remove the bolts and let the pipes hang down a couple of inches. This will free up the exhaust in case there is a plugged catalytic converter. If the misfires go away with the exhaust disconnected, then you found your problem.