Re: 1999 Miata - Check Engine - Help (not resolved)

After replacing the plugs & wires the problem went away for about 30 miles.

It's back.  What's my next step?
How do I check the O2 sensor?
Do I replace the Catalytic Converter?

Where's the best place to get replacement parts (O2 sensor, Catalytic 
Converter)?

Is this something I can easily do myself?

Thanks,
- Pat

"Pat Dreiding" <patdreiding@[EMAIL PROTECTED]
> wrote in message 
news:SYMsj.343$Cs.318@[EMAIL PROTECTED]
>I need a few words of wisdom about my '99.   It has 65K miles on it. 
About 
>a week ago I did something that I believe was very stupid.   I cleaned my

>engine by hosing it down.  The car ran ok for a little while, but then 
>stopped.  The engine light was on. Yes - you guessed it.  Water in the
plug 
>wells.  Ugh!  I spend the time to remove the water and dry the wires &
plug 
>wells.  The car was running fine for another few days afterwards and then

>the check engine light returned.  The autozone tech told me the trouble 
>shooting error code is P0420., which is:  "Catalyst efficiency low-bank 
>  - the oxygen sensors monitor the catalytic converters ability to store 
>oxygen.
> Possible causes are:
> 1. Catalytic converter defective (Failure possibly due to #2, 3, or 4);
> 2. Engine msfire or running condition;
> 3. Large vacuum leak;
> 4.  Engine oil leakage into exhaust-value guide seals, piston rings
>
> Any suggestions on approach to uderstanding and fixing the problem?
>
> I've been considering replacing the plugs & wires.  Is this the correct 
> first step?
>
> Thanks,
> - Pat