06-01-2007, 07:43 AM
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Karting
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Join Date: Sep 2006
Location: Montreal,
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512TR: Pros/cons removing 02
sensors with Test pipes/exhaust
Hey everyone...
I have a 94 512TR... recently fitted
with test pipes and performance
exhaust. What are the pros/cons of
disconnecting the 02 sensors.
thanks
Manny
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Karting
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Join Date: Jul 2005
Location: Richland
Full Name: Jeff Pintler
Posts: 120
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From my limited understanding of how
Motronic systems work, you need the
lamda sensor to monitor the air/fuel
to get the best performance from the
motor. Without the sensor data, the
computer works from a chart that is
based on the stock muffler. I
think the emissions requirements are
not checked above 3000 rpm so the
system uses "chart" values above 3k
rpm. Most of the time motors are
below 3k and to be safe, I would
think the system would be rich
although with a free flow exhaust,
the system might be leaner?! Anyway,
the best way to check would be take
it to a dyno. On the other hand, it
is easy to TIG weld a threaded plug
(18x1.5 i think) onto the test pipes
and install the lamda sensor and
even the thermocouple. Modern fuel
injection systems need to sense the
dithering signal from the lamda
sensor to make the best power and
not burn valves, maybe holes in
pistons or fowl spark plugs. My 348
had a bad fuel rail vacuum pressure
sensor and the system was so rich
the cat converter started to melt.
Using the sensors is cheap
insurance. YMMV
Jeff Pintler
89 348tb, 86tr
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Formula Junior
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Location: Lynchburg, VA
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The O2 sensors are before the main
cats, so I would leave them in.
Unlike OBD2 which adds sensors after
the cats (and in many other areas)
the O2 sensors here just help the
engine run with the best mixture, as
Jeff describes. You will not get
more power, and you will not run as
clean either. Just my 1.5 cents.
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F1 Veteran
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Join Date: Nov 2001
Location: Planet Clair
Full Name: Funk Soul
Brutha
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Leave the O2 sensors, you need them.
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Karting
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well.. I just got my
car back.. and the garage
disconnected my O2 sensors... cause
it was causing my "slow down cyl
7-12" light to blink, and this would
make me loose engine power under
3200rpm.
now that the O2 sensors are
unplugged... car runs great... but
everyone is telling me that the car
should run properly with the O2
sensors on, even though I have test
pipes...
now I am all confused.
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Join Date: Jul 2005
Full Name: RP
Posts: 146
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Your slow down light
is triggered by the cat fire sensors
(thermocouple) and do not impact the
running condition of the car. The 02
sensors,
on the other hand, control the fuel
condition of the car via sampling of
the exhaust gas.
If the sensors that were
disconnected turned off the light,
then the thermocouples were un
plugged and the O2 sensors are still
active, just not
reading.
I too have a 512TR, and removed the
cats, welded in the O2 plug fitting.
I then took the thermocouple sensors
and wire tied them to the frame
tubes behind the rear wheels.
You probably got the slow down light
because the thermocouple sensor was
laying directly on the exhaust pipe.
I concur with everyone else, it is
critical to have the 02 sensor
tapped into the exhaust gas stream.
The thermocouples you can live
without, but
without the O2 sensors you will run
very rich, likely foul plugs over
time.
RP
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Quote:
Originally Posted by
kx5fast
Your
slow down light is
triggered by the cat
fire sensors
(thermocouple) and
do not impact the
running condition of
the car.
The 02 sensors, on
the other hand,
control the fuel
condition of the car
via sampling of the
exhaust gas.
If the sensors that
were disconnected
turned off the
light, then the
thermocouples were
un plugged and the
O2 sensors are still
active, just not
reading.
I too have a 512TR,
and removed the
cats, welded in the
O2 plug fitting.
I then took the
thermocouple sensors
and wire tied them
to the frame tubes
behind the rear
wheels.
You probably got the
slow down light
because the
thermocouple sensor
was laying directly
on the exhaust pipe.
I concur with
everyone else, it is
critical to have the
02 sensor tapped
into the exhaust gas
stream. The
thermocouples you
can live without,
but without the O2
sensors you will run
very rich, likely
foul plugs over
time.
RP
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umm... great.... what do I do
then... get new O2 sensors? can
someone spec me a part number or
something?
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F1 Veteran
Consultant
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Join Date: May 2005
Location: Alabama
Full Name: Click On The
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Posts: 6,748
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Your
512TR probably has Motronic 2.7 ecus.
In that case, your O2 sensors are
ignored under two conditions: cold
engine and Wide Open Throttle (WOT)
at any temp.
There's little incentive to
disconnect O2 sensors under M2.7.
You might want to disconnect them
momentarily as part of a diagnostic
test
(in which case, M2.7 will start
"guessing" at the correct air/fuel
ratio by using its onboard fuel
tables).
Well, that test will either tell you
to change out bad O2 sensors or else
that your problem is somewhere else.
With a cold engine at any throttle
load, or a full throttle at any
engine temperature, you aren't going
to be able to tell the difference in
having or not having working,
connected O2 sensors. This
information should help you decide
if your driving experience hints
that you need or don't need new O2
sensors (e.g. bad O2 sensors
typically start surging or lugging
your speed a bit when the engine is
warm and you are trying to maintain
a constant speed).
But with a warm engine at idle or
partial throttle, having no O2
sensors connected/working is going
to put your car into the guessing
game.
If
your car guesses too lean (could
burn your valves) or too rich (could
burn up a cat, except, your cats are
gone - or could foul your spark
plugs) then you will have
maintenance issues due to
disconnecting said O2 sensors.
You won't gain more power, and you
won't fix problems by disconnecting
O2's. Disconnecting O2's is useful
as a diagnostic test and that's
about it.
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Karting
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Location: Clearwater, FL
Full Name: Kenneth J.
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Quote:
Originally Posted by
MannyGMT2
umm... great....
what do I do then...
get new O2 sensors?
can someone spec me
a part number or
something?
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First off, get the old o2 sensors
back from these so called Ferrari
mechanics.....The bosch replacements
are about $250.00 each.
You need the sensors, your problem
is not with your o2 sensors. I have
seen you post elsewhere about your
ongoing problem.
When the problem started were you
popping thru your exhaust on de
acceleration? And problems with
running on cold start?
If so, sounds more like a fuel
balance and adjustment.
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Quote:
Originally Posted by
KENCO
First
off, get the old o2
sensors back from
these so called
Ferrari
mechanics.....The
bosch replacements
are about $250.00
each.
You need the
sensors, your
problem is not with
your o2 sensors. I
have seen you post
elsewhere about your
ongoing problem.
When the problem
started were you
popping thru your
exhaust on de
acceleration? And
problems with
running on cold
start?
If so, sounds more
like a fuel balance
and adjustment.
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great.. I am nervous
again.
My problem was that I didn't have
any power under 3200rpm... and slow
down cyl 7-12 would blink or light
up under 3200rpm...... as soon as
the light would shut off, you can
hear the engine like switch into a
different mode, like its really
turned on.... the car would return
to the normal beast that it should
be.
When the slow down light would
blink, the car would sputter and
cough etc... always under
3200rpm....even after 2 hours of
driving, and I wasn't accelerating
that hard.
On cold start... umm.. i don't
recall, but i think the problem was
still there. I only drove the car
for one day with this problem and
returned to the garage. Now that the
O2 sensors are unplugged, everything
seems fine.
They did not remove the O2 sensors,
they just unplugged them
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Quote:
Originally Posted by
MannyGMT2
great.. I am nervous
again.
My problem was that
I didn't have any
power under
3200rpm... and slow
down cyl 7-12 would
blink or light up
under 3200rpm......
as soon as the light
would shut off, you
can hear the engine
like switch into a
different mode, like
its really turned
on.... the car would
return to the normal
beast that it should
be.
When the slow down
light would blink,
the car would
sputter and cough
etc... always under
3200rpm....even
after 2 hours of
driving, and I
wasn't accelerating
that hard.
On cold start...
umm.. i don't
recall, but i think
the problem was
still there. I only
drove the car for
one day with this
problem and returned
to the garage. Now
that the O2 sensors
are unplugged,
everything seems
fine.
They did not remove
the O2 sensors, they
just unplugged them
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Well, plug them back in to see if it
still runs ok.
As others suggest, they have nothing
to do with your slow down light.
Check plug wires, coil
wires.........because it sounds like
something that just started
happening, not an ongoing issue.
I purchased an 87 TR that had many
of the same issues, I am at the end
(hopefully) of sorting them out,
some of which were, bad coil wires,
melted precats, melted cat, bad O2
sensor, unplugged vacuum lines, fuel
mixture off, balance
off................it only takes one
tiny thing to mess everything up
with these cars.
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Formula 3
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Remember 02 sensor (Lambda) is
nothing but a temp sensor, it sense
the temperature of the exhaust
before or after the cat or sometimes
both to determine if it's rich
(cooler side) or lean (hotter side).
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Karting
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Quote:
Originally Posted by
miketuason
Remember 02 sensor
(Lambda) is nothing
but a temp sensor,
it sense the
temperature of the
exhaust before or
after the cat or
sometimes both to
determine if it's
rich (cooler side)
or lean (hotter
side)
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Ok, I have some more info to
share...
Apparently the Left side of the
engine is running hotter than the
right side (which side of the engine
is cyl 7-12 anyway?)
When i look at the stainless steel
test pipes. . connected to the left
side of the engine became tarnished
(rainbow look)... where as the test
pipes on the right side are still
nice and mirror like finish. Is this
an indication of higher temp on the
left side?
I also noticed the muffler is REALLY
HOT... even the garage mentioned to
me they were surprised that the
muffler got that hot... (X-OST)
...engine temp seems to run fine
according to the gauge, cooling fans
kick in as normal.
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Karting
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Quote:
Originally Posted by
MannyGMT2
Ok, I
have some more info
to share...
Apparently the Left
side of the engine
is running hotter
than the right side
(which side of the
engine is cyl 7-12
anyway?)
When i look at the
stanless steel test
pipes. . connected
to the left side of
the engine became
tarnished (rainbow
look)... where as
the test pipes on
the right side are
still nice and
mirror like finish.
Is this an
indication of higher
temp on the left
side?
I also noticed the
muffler is REALLY
HOT... even the
garage mentioned to
me they were
surprised that the
muffler got that
hot... (X-OST)
...engine temp seems
to run fine
according to the
guage, cooling fans
kick in as normal.
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Sounds like a fuel
mixture problem.
Did this condition just start to
happen? Or was it like that when you
purchased the car? Or did it start
when you put the exhaust on?
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Karting
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Quote:
Originally Posted by
KENCO
Sounds like a fuel
mixture problem.
Did this condition
just start to
happen? Or was it
like that when you
purchased the car?
Or did it start when
you put the exhaust
on?
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I purchased the car in Nov 2006, car
was all original 94 512TR.. with
2,000miles. Car ran really well...no
issues, but needed timing belts
badly.
Did a full major on it over the
winter period, timing belts, water
pump..etc.. and I had test pipes and
X-OST installed.
Got the car back about 3 weeks ago,
drove one day with it, and got the
issues .. under 3200rpm.. no power,
slow down light
illuminates..etc..etc..
Brought back the car, they unplug
the 02 sensors at the burn box.. car
seems to run very well now. However,
I do notice that the muffler is
REALLY hot... maybe its supposed to
run hot.. no clue.
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F1 Veteran
Consultant
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Join Date: May 2005
Location: Alabama
Full Name: Click On The
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Sounds like mistimed cams and/or a
sealing problem with exhaust
manifold/valves to me.
For instance, a hole in an exhaust
header could allow outside air into
your exhaust stream. Well, an
"outside exhaust air leak" could be
your problem.
The extra Oxygen from allowing
outside air into your exhaust would
be detected by the O2 sensor, which
would tell the computer on that side
of your engine to add more fuel,
which would make that side (in
reality) too rich, which would in
turn heat up a cat and trigger a cat
over temp warning, which the
computer would then use to shut down
half of your engine.
Disconnecting your O2 sensors in
that case would cause your engine to
run better because the
factory-stored fuel tables would be
closer to what your engine wanted in
that case than would the feedback
from the O2 sensors (because they
would be getting outside air that
the engine itself never saw).
So before I pulled the engine
looking at cam timing, I'd look for
an exhaust leak or a burned valve
problem.
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Quote:
Originally Posted by
No Doubt
Sounds like mistimed
cams and/or a
sealing problem with
exhaust
manifold/valves to
me.
For instance, a hole
in an exhaust header
could allow outside
air into your
exhaust stream.
Well, an "outside
exhaust air leak"
could be your
problem.
The extra Oxygen
from allowing
outside air into
your exhaust would
be detected by the
O2 sensor, which
would tell the
computer on that
side of your engine
to add more fuel,
which would make
that side (in
reality) too rich,
which would in turn
heat up a cat and
trigger a cat over
temp warning, which
the computer would
then use to shut
down half of your
engine.
Disconnecting your
O2 sensors in that
case would cause
your engine to run
better because the
factory-stored fuel
tables would be
closer to what your
engine wanted in
that case than would
the feedback from
the O2 sensors
(because they would
be getting outside
air that the
engine itself never
saw).
So before I pulled
the engine looking
at cam timing, I'd
look for an exhaust
leak or a burned
valve problem.
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Agreed, something is
making it run rich, could be outside
air, but if the same mechanics who
just pull the O2 sensors to fix the
problem are the same who did the
engine service, it very well could
be a multitude of things.
If you are DIY guy, you could
probably start with some simple
basic diagnoses.
Ferrari chat is a great way to get
very helpful advice, but if it were
me, I would take it back and make
them repair it. Or maybe someplace
that can repair it correctly.
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Karting
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Quote:
Originally Posted by
KENCO
Agreed, something is
making it run rich,
could be outside
air, but if the same
mechanics who just
pull the O2 sensors
to fix the problem
are the same who did
the engine service,
it very well could
be a multitude of
things.
If you are DIY guy,
you could probably
start with some
simple basic
diagnoses.
Ferrari chat is a
great way to get
very helpful advice,
but if it were me, I
would take it back
and make them repair
it. Or maybe
someplace that can
repair it correctly.
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Yup, this F-chat is helping me out
big time. Unfortunately, there are
limited places where I can bring
this car.... Ferrari dealer told me
to bring them the car in sometime in
July... I hestate to bring it there,
cause.. most of their cars are all
the newer models.. less than a
handfull of 512TR's in our city.
so looks like its going to be DIY
diagnosis.. then bring it back to
the garage that did the service ...
anyway.. its F1 Grand Prix week
here, I am going to try and relax
and enjoy the festivities here!
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Karting
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Join Date: Jul 2005
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Full Name: Jeff Pintler
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After reading most of the other
posts, you probably know that the
sensors are needed. Any "mechanic"
that disconnects sensors to fix a
problem shouldn't repair your car.
Do some research on Lamda sensors
(they sense oxygen levels) and
thermocouples (sense temperatures)
and buy some books on Bosch fuel
injection systems. We all started
exactly where you are at right now.
Be careful of some mechanics and
their advice. There is lots of
information on trouble shooting the
"slow down warning lamps" in the
archives.
Jeff Pintler
89 348tb, 86 tr
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Quote:
Originally Posted by
Jeff Pintler
After reading most
of the other posts,
you probably know
that the sensors are
needed. Any
"mechanic" that
disconnects sensors
to fix a problem
shouldn't repair
your car. Do some
research on Lamda
sensors (they sense
oxygen levels) and
thermocouples (sense
temperatures) and
buy some books on
Bosch fuel injection
systems. We all
started exactly
where you are at
right now. Be
careful of some
mechanics and their
advice. There is
lots of information
on trouble shooting
the "slow down
warning lamps" in
the archives.
Jeff Pintler
89 348tb, 86 tr
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well.. the response I got from the
garage was that... they needed to
disconnect the O2 sensors, cause the
new test pipe and exhaust are making
the ECU's reading go crazy, and the
ECU can not adjust to the new air
flow cause of the test
pipes/exhaust.
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F1 Veteran
Consultant
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Join Date: May 2005
Location: Alabama
Full Name: Click On The
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Quote:
Originally Posted by
MannyGMT2
well.. the response
I got from the
garage was that...
they needed to
disconnect the O2
sensors, cause the
new test pipe and
exhaust are making
the ECU's reading go
crazy, and the ECU
can not adjust to
the new air flow
cause of the test
pipes/exhaust.
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Except of course, the ecus *Are*
adjusting to the new air flow with
your O2's disconnected...which is to
say, what they told you makes no
sense.
It's probably a bit like when you
were back in High School on a hot
date and you would tell the girl
just about anything to get into her
pants at the moment. Well, people
still do that long after they grow
up...on a variety of things besides
dating (still amounts to a screw job
though).
Why are the O2's causing the engine
to run badly? O2's tell the ecus to
lean or enrich the fuel supply to
your engine. If your O2's are
causing your engine to run badly,
then they are *erroneously*
signaling your ecus.
For instance, if your spark plug
wires are cracked...only making good
contact at the higher voltages seen
at high rpms, then you are going to
have some cylinders that aren't
always getting a good spark...so
they are dumping extra fuel into
your exhaust...which your O2's would
interpret as running too rich...so
your O2's would tell your ecus to
lean the mixture to your
engine...except, the cylinders that
*are* getting a good spark would see
that diminished fuel supply as a bad
thing.
...And it would go the other way,
with O2's telling the ecus to add
fuel, if outside air was entering
your engine's exhaust stream via an
air leak...which would again cuase a
poor running engine.
Thus, the O2's and the poor running
engine combine to tell you that you
have an engine problem that isn't
being addressed.
When you disconnect the O2's, then
the extra fuel or air in your
exhaust is being ignored. Your
engine therefor runs decent (based
on the stored "guesses" for air/fuel
mixture that the factory placed in
your ecu chips)...but the underlying
problem is still there (i.e. your
engine isn't getting a good spark,
bad cam timing, or else outside air
is entering your exhaust via a
leak).
Right now you don't know if you have
an exhaust leak or if you have a bad
spark, and with your O2's
disconnected, the worst of the
symptoms of either problem will be
masked somewhat (though bad spark
problems and exhaust leaks *always*
get worse over time, so the problem
won't be masked forever).
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Quote:
Originally Posted by
No Doubt
Except of course,
the ecus *Are*
adjusting to the new
air flow with your
O2's
disconnected...which
is to say, what they
told you makes no
sense.
It's probably a bit
like when you were
back in High School
on a hot date and
you would tell the
girl just about
anything to get into
her pants at the
moment. Well, people
still do that long
after they grow
up...on a variety of
things besides
dating (still
amounts to a screw
job though).
Why are the O2's
causing the engine
to run badly? O2's
tell the ecus to
lean or enrich the
fuel supply to your
engine. If your O2's
are causing your
engine to run badly,
then they are
*erroneously*
signaling your ecus.
For instance, if
your spark plug
wires are
cracked...only
making good contact
at the higher
voltages seen at
high rpms, then you
are going to have
some cylinders that
aren't always
getting a good
spark...so they are
dumping extra fuel
into your
exhaust...which your
O2's would interpret
as running too
rich...so your O2's
would tell your ecus
to lean the mixture
to your
engine...except, the
cylinders that *are*
getting a good spark
would see that
diminished fuel
supply as a bad
thing.
...And it would go
the other way, with
O2's telling the
ecus to add fuel, if
outside air was
entering your
engine's
exhaust stream via
an air leak...which
would again cause a
poor running engine.
Thus, the O2's and
the poor running
engine combine to
tell you that you
have an engine
problem that isn't
being addressed.
When you disconnect
the O2's, then the
extra fuel or air in
your exhaust is
being ignored. Your
engine there for
runs decent (based
on the stored
"guesses" for
air/fuel mixture
that the factory
placed in your ecu
chips)...but the
underlying problem
is still there (i.e.
your engine isn't
getting a good
spark, bad cam
timing, or else
outside air is
entering your
exhaust via a leak).
Right now you don't
know if you have an
exhaust leak or if
you have a bad
spark, and with your
O2's disconnected,
the worst of the
symptoms of either
problem will be
masked somewhat
(though bad spark
problems and exhaust
leaks *always* get
worse over time, so
the problem won't be
masked forever).
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wow.. amazing write up...
so basically, if i go to "another
garage" what tests can I ask them to
perform to verify if
A) cam timing is correct
B) how to check for exhaust leaks
C) Spark verification to the
cylinders
I was told by a couple of mechanics,
that one form of test... with a gas
analyser to determine the values of
different gases before the test
pipes...
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F1 Veteran
Consultant
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Join Date: May 2005
Location: Alabama
Full Name: Click On The
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Posts: 6,748
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If you are confident that your
problem is limited to one side of
your flat-12, then I'd think that
pulling the 6 spark plugs on that
side would be your first choice.
Examine those 6 for consistency.
Post their pictures here. See the
spark plug thread in the link in my
signature below. Do those 6 plugs
have identical wear qualities, or do
you see one or two that are quite
different (e.g. oil soaked)?
The answer to the above should help
point you in the right direction
re:spark or no spark problem.
Frankly, I'd do this yourself (for a
variety of reasons). This is
something that you can easily do in
your own garage. Go pull the 6 spark
plugs on your offending side. Photo
them and post the pics here. Then go
read my spark plug thread below.
You'll be amazed.
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