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Infiniti G35 Catalytic Converter Melt Down

Hello. I have a 2005 G35 Infiniti with a bank one catalytic converter failure at 80100 miles. The substrate partially melted and had to be replaced. The CAT was not covered or poisoned, it was melted partially.

I recently had a smog check and noticed some results that were a little peculiar. Perhaps you can help. The NO PPM measured at zero. The HC measured at 25 for 15 mph, 6 at 25mph. CO measured .09 at 15 mph and .06 at 25 mph. Fuel ratio sensor bank one shows .3 volts at cruise and .6 volts bank 2 both upstream. Long term fuel on bank one indicates between 8 and 10 during cruise. Long term fuel on bank 2 is between 7.8 to 9.2 during cruise.

Does the following indicate a false lean reading and thereby enriching the mixture unnecessarily causing a cat failure?

Answer:

You're on track. More than likely this is a false lean condition; meaning either unmetered air is entering the intake manifold and ultimately the combustion chambers, or the MAF sensor is not calculating the volume of air entering the engine, correctly. Inspect the mass air flow sensor for correct values at idle and 2500 rpms and then check for cracked/brittle or disconnected vacuum hoses, and even possibly, defective intake manifold gasket(s). Inspect fuel trim at both idle and while cruising. If short term fuel trim is high during both conditions, suspect a vacuum leak behind or after the throttle plate. It will not hurt to ensure your G35's air fuel ratio sensors are functioning properly either. To check the operating condition of your Infiniti's fuel ratio sensors we recommend conducting a fuel enrichment test using propane. Check that fuel ratio sensor signal voltage switches between .02 when rich and .09 when lean (this is the opposite of the values to check for when testing a regular oxygen sensor) as propane is added and removed. Take extra caution when using propane as it is extremely flammable. posted by SmogTips Support

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