I have a 2000 Toyota Tacoma TRD 3.4 liter with california emissions
and 114,500 mile.P0420 catalyst efficiency below threshold (bank1)
came up on OBDII scanner. My gas mileage seemed to have dropped about
3-4 miles per gallon since check engine light came on. I replaced the
o2 sensor after the two cats a couple years back. From the reading I
have done and people I've talked to it seems my cat maybe clogged. If
I replace the cat with a High Flow cat (MagnaFlow) will it cause
problems with my sensors. And also can I do anything about getting rid
of one of the cats since I live in Pa and have no intentions of going
to Cal. What is the best thing to do to fix this problem. Dealer price
for front and rear cat are $940 and $1045 (not an option).

Thanks in advance for all replies.
-Jason

My inclination is to focus on the sensor before the CAT itself. In my world,
the CAT is very reliable, and if it were to phsically clog, there would be
driveability issue that you would notice before the computer told you there
was a problem.

Surely I'll face argument here, but I have solid reasoning.

If the CAT were to clog, then the flow would diminish, causing a loss of
intake. You would feel the loss of intake.

The sensor that decides efficiency is not looking at the flow, it's looking
at the residual fuel content. The exhaust stream ahead of the CAT contains
stuff that the sensor after the CAT does not want to see. If the CAT is
properly converting the exhaust stream gasses, then the sensor is happy. If
the sensor is not happy, the computer does not know if the sensor itself is
toast or if the CAT is toast, but the display is the same. It is certainly
possible for the CAT to be toast, but I place my pile of poker ships on the
sensor first.

RayO, here, will be able to give a test -- one that I ought to know how to
perform, but my guess at the sensor has always been correct so I haven't
ever done the test that Ray knows. There are O2 Sensors ahead of the CAT
too, but there are codes that will tell you if they (or it, if there is only
one) is not functioning properly. Having said that, Ray's testing procedure
will help you isolate the offending sensor so you replace the proper part.





"jcaru" <Jason.Caruso (AT) gmail (DOT) com> wrote

On Apr 14, 2:32 pm, "jcaru" <Jason.Car... (AT) gmail (DOT) com> wrote:
I'd definitely suspect the front O2 sensor before condemning the cat.
The drop in gas mileage is another strong indicator of a lazy O2
sensor. The front O2 sensor monitors the oxygen content of the
exhaust gas in the manifold and should normally be switching rapidly
between about 200 millivolts and 800 mv as the computer rapidly
adjusts the fuel/air ratio to optimize the fuel mixture. If the cat
is working properly, the rear O2 sensor should output a fairly
constant voltage of about 450mv. The computer compares the switching
rate of the front O2 sensor to that of the rear O2 sensor. If the
switching rates are similiar, it sets the P0420 code under the theory
that the exhaust gas coming out of the cat looks very similiar to
exhaust gas going into the cat and so the catalyst efficienct is below
normal. But if the front O2 sensor gets lazy and starts switching too
slowly, then the P0420 code is set and the problem is the sensor and
not the cat. It is also possible that the front O2 sensor heater
circuit is malfunctioning which would cause the O2 sensor to not get
hot enough, especially at idle, to work properly. However, if that
were true, there is usually a separate code for that. Before spending
a ton of money on a cat, it would be very worthwhile to put the
vehicle on a scan tool and watch the operation of the O2 sensors and
observe that the O2 heaters are on. If you can't do that, investing
in a $50-75 OEM front O2 sensor first before opting for the $1000 fix
would seem to make good economic sense. Good luck. Al

Or, if you still have the old O2 sensor, take the new one and put it in
front of the cat and put the old one back in the rear position.

It's cheap if you still have the old part.

Paul.
"al" <abuonag (AT) msn (DOT) com> wrote

On Apr 16, 9:04 pm, "Paul." <paul.blomb... (AT) cox (DOT) net> wrote:
Thanks for all the input. I have a good mechanic that will help the
truck pass emissions if you know what I mean. Say it is the front 02
sensor. Will and after market Cat mess with my sensors at all. And
also how do I place the voltmeter on the sensor to test them??

======
======
On Apr 16, 9:26�pm, jcaru <Jason.Car... (AT) gmail (DOT) com> wrote:
======
your SECOND sentence.....
yeah..i know what you mean...he's not a good mechanic,
because a good mechanic would NEVER MAKE...a
vehicle pass emisions.


regardless.....

here....more than you need to know, and more
than you deserve because of your intent on be'n
a stick in the mud about global warm'n...
oh yeah..i know...there is NO global warm'n...
sure...sure.


..
http://www.smp-training.com/Counterm.../sensor01.html


~:~
MarshMonster
~slaps you side the head....sips his crownroyal.....hopes
you come to yer senses....or sensors...or convertors~

On Apr 16, 10:26 pm, jcaru <Jason.Car... (AT) gmail (DOT) com> wrote:
If you really need a cat, which I doubt, aftermarket catalytic
converters are definitely the way to go. Federal law requires minimum
standards for them. I believe, though I'm not sure, that they must be
designed not only to adequetly reduce emissions but to last something
like eight years. I don't recall the exact number of years. There's
no compatability issue whatseover. Thanks for that very informative
website with the primer on O2 sensors. If you want to test the
sensor, a scan tool is really the only practical way to do it. The
very informative website that another reply mentioned describes a
voltmeter test but you'd have to tap into the wiring somehow and have
a voltmeter with a fast response. It's also possible to bench test it
with a blowtorch and a voltmeter but that's a bit of a Rube Goldberg
approach. I presume the "good mechanic" can put the vehicle on his
scan tool and not just conveniently look the other way during an
emissions test.

The code you got does not mean the cat is clogged, it means that your OBDII
is not reading the correct differences in gasses before and after the cats.
One cause for this is leaks in the exhaust between the 02 sensors. Another
cause is the platinum has worn off the ceramic matrix and the cat is no
longer functioning properly according to OBDII standards. You can replace
the cats with the Magnaflow cats and they will function as factory cats. I
think that they are 50 state legal, but they may not pass CA because they
are not factory (not because they do not function at factory specs, because
they do). Inspect your exhaust and insure that the gaskets under the 02
sensors and between the cats are sealing. If there are no leaks, I would
replace the cats with the Magnaflow cats. They are smaller than stock so a
length of exhaust pipe is needed to fill in the gap. I got mine from
hotexhaust for about $120 each and installation was about $50.

Disregard retards pissing about global warming. When they explain how
global warming on Mars has nothing to do with warming on earth, maybe then
they will have something to say worth listening to.



"jcaru" <Jason.Caruso (AT) gmail (DOT) com> wrote