2001-2006 Ford Escape and Mazda Tributes as well as 2005-2006 Mercury Mariners equipped with 3.0L engines have exhibited some "full circle" problems I would like to address in this TechNote.
It is not uncommon for all three catalytic converters to become clogged on these vehicles, one of the major causes being coil-on-plug failures.
The second most common cause though is the failure of the EGR gaskets....
The EGR valve on these vehicles sits atop the intake manifold on a conventional graphite gasket, but there is also an O-ring that seals the tube on the intake manifold to the valve itself.
The original O-rings were prone to failure which caused a vacuum leak and eventual misfire causing the manifold converters to break and eventually clog the undercar converter. Often when this happened, the exhaust pressure built up in the EGR tube and blew the EGR valve itself apart. That is what I mean by "full circle". If this were to happen, the root cause is repaired by default. New valve + new gaskets = effective repair.
There is an updated set of gaskets that must be installed, even if the very common catastrophic EGR valve failure is not present.
Mazda Part Numbers:
Ford Part Numbers:
Gasket E6AZ 9D476-B
O-Ring YL8Z 9J469-AA
(The new style O-Rings are blue in color)
It is essential that these gaskets are replaced along with the converter.
If this gasket failure was related to the original cause of converter failure and is left un-repaired, we've seen replacement converters destroyed in as little as a couple of hundred miles, rendering the vehicle inoperable, causing the need for it to be towed to a repair facility.