2004 Mercury Marquis need to know correct catalytic convert

PLAD2CARPROS

MEMBER
2004 MERCURY MARQUIS
V8
2WD
AUTOMATIC
99,000 MILES

I have been told my rattling is BOTH my catalytic converters are bad. I have been to dealers, service centers, muffler shops - all have very different suggestions and prices. I have looked online and besides much better parts costs, I find there are at least
6 different varieties to choose from: CALIF OR 49-STATE LEGAL; FULL PIPE + CONVERTERS OR INDIVIDUAL CONVERTER UNITS; DRIVER, PASSENGER, FRONT, REAR CONVERTERS.
My car is OBDII compliant -BUT it has not, is not and will not be registered in CALIF.

So - 1st: is a 49-state legal an ok (mechanically and legally) substitue? Will I have to deal with the CEL light being on when nothing is really wrong? 2nd: is it best to get the FULL UNITS - driver and passenger, or is it better to try and figure out which of the 2/4 converters are bad? Are there really pre and post converters or is the rear unit the muffler?

I am prepared to buy the 49-state legal FULL UNITS - driver and rear - and I have been quoted prices ranging from 500.00 - 2500.00 - way too much variance.

1 Reply

SERVICE WRITER

MECHANIC
9,123 POSTS

There is a white sticker under the hood that will say if it is CA compliant or just federal.

They are different designs in most cases and do not interchange.

You want direct fit, not universal. This will be with the front pipe.

Take a rubber mallet and rap it on each converter and listen for the rattle. Be sure it isn't just the sheild rattling.

I would use AP brand myself.

I onl;y see 2 converters on this one. Rear ones are resonators and mufflers.