Check Engine Light w/PO420.

[Michael Roberts]

Hi fellow STers,

About 6 weeks ago my CEL came on w/PO420 in memory. MPG went from 180+ miles on half-a-tank to about 160 miles on same fuel qty. No smoke or erratic running scenario.

My 04ST has the RT Y-Pipe and Single Cat. Engine has run beautifully for two years now.

The engine was running fine and I checked all the obvious but found nothing.

So I'm thinking I must have had debris in one of the fuel injectors and over-rich on one cyl. I disconnected the aft portion of my new/recently installed fuel filter and drained it and then squirted Evinrude Engine Tuner into the filter and forward fuel line to clean the system. About a week later, the CEL is off.

Have I fixed my problem?

Do I need to be thinking about fuel injectors?

Or is it just the quality of fuel we're getting here at home?

Any suggestions?

 

[scott degroot]

A P0420 is a catalytic converter code. Should have absolutely no affect on fuel mileage unless the cat is starting to plug. If you have had the current cat on there for 2 years then it may be starting to go bad as most aftermarket cats are only good for about 2 years.

 

[Michael Roberts]

l1tech,

My MPG is back to where it should be after the CEL has gone off. I don't think I have a Cat issue because of this. According to my research, the PO420 is indicative of incorrect mixture on cyl bank #1. Thus my concern for a fuel injector being off.nline:

 

[scott degroot]

I can tell you with 100% confidence that a P0420 is a catalyst system efficency below threshold bank 1 code. Incorrect mixture codes would be P0171, P0172, P0174 and P0175 depending on if the mixture was rich or lean and on what bank. Is it possible that you got the code number wrong?