so instead of checking for a $10 gasket, you just went ahead and dropped $400 on something that may/may not have been bad?

Brilliant.

 

No, you misunderstood me. I had 2 exhaust shop's check for leaks and they could not find any. What I was saying is I did not switch the 02 sensors to see if it would be a bank 2 code nor did I run the Seafoam through the intake. All 5 dealers I spoke with said it is the cats. 02 sensors would set a specific code and not a generic code.

 

P0420 - Check for exhaust leak. Bad post oxygen sensor. Last would be bad cat.

 

Update:
500 miles later and no more CEL. I took the chance that it was drivers side cat and not the 02 sensor. I was told by multiple dealers that 02 sensors set their own specific codes and not generic ones but I am not sure if this info is specific for later model LS400's or specific to the pre-cat 02 sensors. One thing I do notice with new Magnaflow cats though is that the mufflers are a bit louder when driving with the windows down.

 

hey PD - will seafoaming hurt my awesome high performance plugs that have super power and super gas mileage and the world's smallest electrode?

 

Anyone have the Magnaflow part # for 90 LS?

Direct Fit # 37162