O2 sensor
10-03-2003, 01:19 AM
#11
Guest
Posts: n/a
Re: O2 sensor
Actually, the PCM will use downstream O2 input to "fine tune" fuel trim in
addition to monitoring the cat.
The OP didn't say what engine he had, but there's a TSB for 4.0L engines
concerning decarbonizing the combustion chamber and revised valve springs.
In message <bvWeb.37369$gv5.16849@fed1read05>, "Jerry Bransford" wrote:
>The downstream 02 sensor, unlike the upstream 02 sensor, has no ability to
>adjust the fuel mixture or for that matter, anything about how the engine
>runs. Its sole function is to check the cat for proper function and display
>a Check Engine light if it detects that the cat has gone bad.
>
>Jerry
addition to monitoring the cat.
The OP didn't say what engine he had, but there's a TSB for 4.0L engines
concerning decarbonizing the combustion chamber and revised valve springs.
In message <bvWeb.37369$gv5.16849@fed1read05>, "Jerry Bransford" wrote:
>The downstream 02 sensor, unlike the upstream 02 sensor, has no ability to
>adjust the fuel mixture or for that matter, anything about how the engine
>runs. Its sole function is to check the cat for proper function and display
>a Check Engine light if it detects that the cat has gone bad.
>
>Jerry
10-03-2003, 01:19 AM
#12
Guest
Posts: n/a
Re: O2 sensor
Actually, the PCM will use downstream O2 input to "fine tune" fuel trim in
addition to monitoring the cat.
The OP didn't say what engine he had, but there's a TSB for 4.0L engines
concerning decarbonizing the combustion chamber and revised valve springs.
In message <bvWeb.37369$gv5.16849@fed1read05>, "Jerry Bransford" wrote:
>The downstream 02 sensor, unlike the upstream 02 sensor, has no ability to
>adjust the fuel mixture or for that matter, anything about how the engine
>runs. Its sole function is to check the cat for proper function and display
>a Check Engine light if it detects that the cat has gone bad.
>
>Jerry
addition to monitoring the cat.
The OP didn't say what engine he had, but there's a TSB for 4.0L engines
concerning decarbonizing the combustion chamber and revised valve springs.
In message <bvWeb.37369$gv5.16849@fed1read05>, "Jerry Bransford" wrote:
>The downstream 02 sensor, unlike the upstream 02 sensor, has no ability to
>adjust the fuel mixture or for that matter, anything about how the engine
>runs. Its sole function is to check the cat for proper function and display
>a Check Engine light if it detects that the cat has gone bad.
>
>Jerry
10-03-2003, 01:33 AM
#13
Guest
Posts: n/a
Re: O2 sensor
Why do I seem to recall that my '97 FSM says the downstream sensor is only
there to monitor the cat, and that the upstream sensor checks and tells the
PCM how to adjust the injector's pulse duration for proper fuel mixture?
Jerry
--
--
Jerry Bransford
To email, remove 'me' from my email address
KC6TAY, PP-ASEL
See the Geezer Jeep at
http://members.***.net/jerrypb/
"bllsht" <nospam@invaliddot.net> wrote in message
news:4n0qnvg1k6p53k6f6r0n3a62i5jaju8d8d@4ax.com...
> Actually, the PCM will use downstream O2 input to "fine tune" fuel trim in
> addition to monitoring the cat.
>
> The OP didn't say what engine he had, but there's a TSB for 4.0L engines
> concerning decarbonizing the combustion chamber and revised valve springs.
>
>
>
> In message <bvWeb.37369$gv5.16849@fed1read05>, "Jerry Bransford" wrote:
>
> >The downstream 02 sensor, unlike the upstream 02 sensor, has no ability
to
> >adjust the fuel mixture or for that matter, anything about how the engine
> >runs. Its sole function is to check the cat for proper function and
display
> >a Check Engine light if it detects that the cat has gone bad.
> >
> >Jerry
>
there to monitor the cat, and that the upstream sensor checks and tells the
PCM how to adjust the injector's pulse duration for proper fuel mixture?
Jerry
--
--
Jerry Bransford
To email, remove 'me' from my email address
KC6TAY, PP-ASEL
See the Geezer Jeep at
http://members.***.net/jerrypb/
"bllsht" <nospam@invaliddot.net> wrote in message
news:4n0qnvg1k6p53k6f6r0n3a62i5jaju8d8d@4ax.com...
> Actually, the PCM will use downstream O2 input to "fine tune" fuel trim in
> addition to monitoring the cat.
>
> The OP didn't say what engine he had, but there's a TSB for 4.0L engines
> concerning decarbonizing the combustion chamber and revised valve springs.
>
>
>
> In message <bvWeb.37369$gv5.16849@fed1read05>, "Jerry Bransford" wrote:
>
> >The downstream 02 sensor, unlike the upstream 02 sensor, has no ability
to
> >adjust the fuel mixture or for that matter, anything about how the engine
> >runs. Its sole function is to check the cat for proper function and
display
> >a Check Engine light if it detects that the cat has gone bad.
> >
> >Jerry
>
10-03-2003, 01:33 AM
#14
Guest
Posts: n/a
Re: O2 sensor
Why do I seem to recall that my '97 FSM says the downstream sensor is only
there to monitor the cat, and that the upstream sensor checks and tells the
PCM how to adjust the injector's pulse duration for proper fuel mixture?
Jerry
--
--
Jerry Bransford
To email, remove 'me' from my email address
KC6TAY, PP-ASEL
See the Geezer Jeep at
http://members.***.net/jerrypb/
"bllsht" <nospam@invaliddot.net> wrote in message
news:4n0qnvg1k6p53k6f6r0n3a62i5jaju8d8d@4ax.com...
> Actually, the PCM will use downstream O2 input to "fine tune" fuel trim in
> addition to monitoring the cat.
>
> The OP didn't say what engine he had, but there's a TSB for 4.0L engines
> concerning decarbonizing the combustion chamber and revised valve springs.
>
>
>
> In message <bvWeb.37369$gv5.16849@fed1read05>, "Jerry Bransford" wrote:
>
> >The downstream 02 sensor, unlike the upstream 02 sensor, has no ability
to
> >adjust the fuel mixture or for that matter, anything about how the engine
> >runs. Its sole function is to check the cat for proper function and
display
> >a Check Engine light if it detects that the cat has gone bad.
> >
> >Jerry
>
there to monitor the cat, and that the upstream sensor checks and tells the
PCM how to adjust the injector's pulse duration for proper fuel mixture?
Jerry
--
--
Jerry Bransford
To email, remove 'me' from my email address
KC6TAY, PP-ASEL
See the Geezer Jeep at
http://members.***.net/jerrypb/
"bllsht" <nospam@invaliddot.net> wrote in message
news:4n0qnvg1k6p53k6f6r0n3a62i5jaju8d8d@4ax.com...
> Actually, the PCM will use downstream O2 input to "fine tune" fuel trim in
> addition to monitoring the cat.
>
> The OP didn't say what engine he had, but there's a TSB for 4.0L engines
> concerning decarbonizing the combustion chamber and revised valve springs.
>
>
>
> In message <bvWeb.37369$gv5.16849@fed1read05>, "Jerry Bransford" wrote:
>
> >The downstream 02 sensor, unlike the upstream 02 sensor, has no ability
to
> >adjust the fuel mixture or for that matter, anything about how the engine
> >runs. Its sole function is to check the cat for proper function and
display
> >a Check Engine light if it detects that the cat has gone bad.
> >
> >Jerry
>
10-03-2003, 01:33 AM
#15
Guest
Posts: n/a
Re: O2 sensor
Why do I seem to recall that my '97 FSM says the downstream sensor is only
there to monitor the cat, and that the upstream sensor checks and tells the
PCM how to adjust the injector's pulse duration for proper fuel mixture?
Jerry
--
--
Jerry Bransford
To email, remove 'me' from my email address
KC6TAY, PP-ASEL
See the Geezer Jeep at
http://members.***.net/jerrypb/
"bllsht" <nospam@invaliddot.net> wrote in message
news:4n0qnvg1k6p53k6f6r0n3a62i5jaju8d8d@4ax.com...
> Actually, the PCM will use downstream O2 input to "fine tune" fuel trim in
> addition to monitoring the cat.
>
> The OP didn't say what engine he had, but there's a TSB for 4.0L engines
> concerning decarbonizing the combustion chamber and revised valve springs.
>
>
>
> In message <bvWeb.37369$gv5.16849@fed1read05>, "Jerry Bransford" wrote:
>
> >The downstream 02 sensor, unlike the upstream 02 sensor, has no ability
to
> >adjust the fuel mixture or for that matter, anything about how the engine
> >runs. Its sole function is to check the cat for proper function and
display
> >a Check Engine light if it detects that the cat has gone bad.
> >
> >Jerry
>
there to monitor the cat, and that the upstream sensor checks and tells the
PCM how to adjust the injector's pulse duration for proper fuel mixture?
Jerry
--
--
Jerry Bransford
To email, remove 'me' from my email address
KC6TAY, PP-ASEL
See the Geezer Jeep at
http://members.***.net/jerrypb/
"bllsht" <nospam@invaliddot.net> wrote in message
news:4n0qnvg1k6p53k6f6r0n3a62i5jaju8d8d@4ax.com...
> Actually, the PCM will use downstream O2 input to "fine tune" fuel trim in
> addition to monitoring the cat.
>
> The OP didn't say what engine he had, but there's a TSB for 4.0L engines
> concerning decarbonizing the combustion chamber and revised valve springs.
>
>
>
> In message <bvWeb.37369$gv5.16849@fed1read05>, "Jerry Bransford" wrote:
>
> >The downstream 02 sensor, unlike the upstream 02 sensor, has no ability
to
> >adjust the fuel mixture or for that matter, anything about how the engine
> >runs. Its sole function is to check the cat for proper function and
display
> >a Check Engine light if it detects that the cat has gone bad.
> >
> >Jerry
>
10-04-2003, 12:01 AM
#16
Guest
Posts: n/a
Re: O2 sensor
Yes, the primary reason for the downstream O2 is to monitor cat converter
efficiency. That was mandated by the OBD II standard. Since they had to
install the 2nd O2 anyway, I guess they thought they'd put it to other uses
also, and they did.
The downstream O2 sensors spend most of their time NOT monitoring the cat. The
cat monitor isn't a continuously running monitor. Once certain enabling
conditions are met, the cat monitor will run, and takes probably less than 30
seconds to complete, and will only run once per trip (key cycle). That leaves a
whole lot of driving time to do "nothing". If they can use that time to improve
fuel economy or emissions they will, and do.
Can't tell ya why you don't remember seeing that, or why they wouldn't tell ya
that in the FSM, but they'd also have you believe that when you look at your oil
pressure gauge, you're seeing actual oil pressure.
In message <PS7fb.38240$gv5.27728@fed1read05>, "Jerry Bransford" wrote:
>Why do I seem to recall that my '97 FSM says the downstream sensor is only
>there to monitor the cat, and that the upstream sensor checks and tells the
>PCM how to adjust the injector's pulse duration for proper fuel mixture?
>
>Jerry
>
>--
efficiency. That was mandated by the OBD II standard. Since they had to
install the 2nd O2 anyway, I guess they thought they'd put it to other uses
also, and they did.
The downstream O2 sensors spend most of their time NOT monitoring the cat. The
cat monitor isn't a continuously running monitor. Once certain enabling
conditions are met, the cat monitor will run, and takes probably less than 30
seconds to complete, and will only run once per trip (key cycle). That leaves a
whole lot of driving time to do "nothing". If they can use that time to improve
fuel economy or emissions they will, and do.
Can't tell ya why you don't remember seeing that, or why they wouldn't tell ya
that in the FSM, but they'd also have you believe that when you look at your oil
pressure gauge, you're seeing actual oil pressure.
In message <PS7fb.38240$gv5.27728@fed1read05>, "Jerry Bransford" wrote:
>Why do I seem to recall that my '97 FSM says the downstream sensor is only
>there to monitor the cat, and that the upstream sensor checks and tells the
>PCM how to adjust the injector's pulse duration for proper fuel mixture?
>
>Jerry
>
>--
10-04-2003, 12:01 AM
#17
Guest
Posts: n/a
Re: O2 sensor
Yes, the primary reason for the downstream O2 is to monitor cat converter
efficiency. That was mandated by the OBD II standard. Since they had to
install the 2nd O2 anyway, I guess they thought they'd put it to other uses
also, and they did.
The downstream O2 sensors spend most of their time NOT monitoring the cat. The
cat monitor isn't a continuously running monitor. Once certain enabling
conditions are met, the cat monitor will run, and takes probably less than 30
seconds to complete, and will only run once per trip (key cycle). That leaves a
whole lot of driving time to do "nothing". If they can use that time to improve
fuel economy or emissions they will, and do.
Can't tell ya why you don't remember seeing that, or why they wouldn't tell ya
that in the FSM, but they'd also have you believe that when you look at your oil
pressure gauge, you're seeing actual oil pressure.
In message <PS7fb.38240$gv5.27728@fed1read05>, "Jerry Bransford" wrote:
>Why do I seem to recall that my '97 FSM says the downstream sensor is only
>there to monitor the cat, and that the upstream sensor checks and tells the
>PCM how to adjust the injector's pulse duration for proper fuel mixture?
>
>Jerry
>
>--
efficiency. That was mandated by the OBD II standard. Since they had to
install the 2nd O2 anyway, I guess they thought they'd put it to other uses
also, and they did.
The downstream O2 sensors spend most of their time NOT monitoring the cat. The
cat monitor isn't a continuously running monitor. Once certain enabling
conditions are met, the cat monitor will run, and takes probably less than 30
seconds to complete, and will only run once per trip (key cycle). That leaves a
whole lot of driving time to do "nothing". If they can use that time to improve
fuel economy or emissions they will, and do.
Can't tell ya why you don't remember seeing that, or why they wouldn't tell ya
that in the FSM, but they'd also have you believe that when you look at your oil
pressure gauge, you're seeing actual oil pressure.
In message <PS7fb.38240$gv5.27728@fed1read05>, "Jerry Bransford" wrote:
>Why do I seem to recall that my '97 FSM says the downstream sensor is only
>there to monitor the cat, and that the upstream sensor checks and tells the
>PCM how to adjust the injector's pulse duration for proper fuel mixture?
>
>Jerry
>
>--
10-04-2003, 12:01 AM
#18
Guest
Posts: n/a
Re: O2 sensor
Yes, the primary reason for the downstream O2 is to monitor cat converter
efficiency. That was mandated by the OBD II standard. Since they had to
install the 2nd O2 anyway, I guess they thought they'd put it to other uses
also, and they did.
The downstream O2 sensors spend most of their time NOT monitoring the cat. The
cat monitor isn't a continuously running monitor. Once certain enabling
conditions are met, the cat monitor will run, and takes probably less than 30
seconds to complete, and will only run once per trip (key cycle). That leaves a
whole lot of driving time to do "nothing". If they can use that time to improve
fuel economy or emissions they will, and do.
Can't tell ya why you don't remember seeing that, or why they wouldn't tell ya
that in the FSM, but they'd also have you believe that when you look at your oil
pressure gauge, you're seeing actual oil pressure.
In message <PS7fb.38240$gv5.27728@fed1read05>, "Jerry Bransford" wrote:
>Why do I seem to recall that my '97 FSM says the downstream sensor is only
>there to monitor the cat, and that the upstream sensor checks and tells the
>PCM how to adjust the injector's pulse duration for proper fuel mixture?
>
>Jerry
>
>--
efficiency. That was mandated by the OBD II standard. Since they had to
install the 2nd O2 anyway, I guess they thought they'd put it to other uses
also, and they did.
The downstream O2 sensors spend most of their time NOT monitoring the cat. The
cat monitor isn't a continuously running monitor. Once certain enabling
conditions are met, the cat monitor will run, and takes probably less than 30
seconds to complete, and will only run once per trip (key cycle). That leaves a
whole lot of driving time to do "nothing". If they can use that time to improve
fuel economy or emissions they will, and do.
Can't tell ya why you don't remember seeing that, or why they wouldn't tell ya
that in the FSM, but they'd also have you believe that when you look at your oil
pressure gauge, you're seeing actual oil pressure.
In message <PS7fb.38240$gv5.27728@fed1read05>, "Jerry Bransford" wrote:
>Why do I seem to recall that my '97 FSM says the downstream sensor is only
>there to monitor the cat, and that the upstream sensor checks and tells the
>PCM how to adjust the injector's pulse duration for proper fuel mixture?
>
>Jerry
>
>--
10-05-2003, 06:58 AM
#19
Guest
Posts: n/a
Re: O2 sensor
From the FSM:
The catalyst monitor uses dual oxygen sensors
(O2S's) to monitor the efficiency of the converter. The
dual O2S's sensor strategy is based on the fact that
as a catalyst deteriorates, its oxygen storage capacity
and its efficiency are both reduced. By monitoring
the oxygen storage capacity of a catalyst, its efficiency
can be indirectly calculated. The upstream
O2S is used to detect the amount of oxygen in the
exhaust gas before the gas enters the catalytic converter.
The PCM calculates the A/F mixture from the
output of the O2S. A low voltage indicates high oxygen
content (lean mixture). A high voltage indicates a
low content of oxygen (rich mixture).
When the upstream O2S detects a lean condition,
there is an abundance of oxygen in the exhaust gas.
A functioning converter would store this oxygen so it
can use it for the oxidation of HC and CO. As the
converter absorbs the oxygen, there will be a lack of
oxygen downstream of the converter. The output of
the downstream O2S will indicate limited activity in
this condition.
As the converter loses the ability to store oxygen,
the condition can be detected from the behavior of
the downstream O2S. When the efficiency drops, no
chemical reaction takes place. This means the concentration
of oxygen will be the same downstream as
upstream. The output voltage of the downstream
O2S copies the voltage of the upstream sensor. The
only difference is a time lag (seen by the PCM)
between the switching of the O2S's.
To monitor the system, the number of lean-to-rich
switches of upstream and downstream O2S's is
counted. The ratio of downstream switches to
upstream switches is used to determine whether the
catalyst is operating properly. An effective catalyst
will have fewer downstream switches than it has
upstream switches i.e., a ratio closer to zero. For a
totally ineffective catalyst, this ratio will be one-toone,
indicating that no oxidation occurs in the device.
The system must be monitored so that when catalyst
efficiency deteriorates and exhaust emissions
increase to over the legal limit, the MIL will be illuminated.
--
Dave Milne, Scotland
'99 TJ 4.0 Sahara
"Jerry Bransford" <jerrypb@mecox.net> wrote in message
news:PS7fb.38240$gv5.27728@fed1read05...
: Why do I seem to recall that my '97 FSM says the downstream sensor is only
: there to monitor the cat, and that the upstream sensor checks and tells
the
: PCM how to adjust the injector's pulse duration for proper fuel mixture?
:
: Jerry
:
: --
: --
: Jerry Bransford
: To email, remove 'me' from my email address
: KC6TAY, PP-ASEL
: See the Geezer Jeep at
: http://members.***.net/jerrypb/
:
: "bllsht" <nospam@invaliddot.net> wrote in message
: news:4n0qnvg1k6p53k6f6r0n3a62i5jaju8d8d@4ax.com...
: > Actually, the PCM will use downstream O2 input to "fine tune" fuel trim
in
: > addition to monitoring the cat.
: >
: > The OP didn't say what engine he had, but there's a TSB for 4.0L engines
: > concerning decarbonizing the combustion chamber and revised valve
springs.
: >
: >
: >
: > In message <bvWeb.37369$gv5.16849@fed1read05>, "Jerry Bransford" wrote:
: >
: > >The downstream 02 sensor, unlike the upstream 02 sensor, has no ability
: to
: > >adjust the fuel mixture or for that matter, anything about how the
engine
: > >runs. Its sole function is to check the cat for proper function and
: display
: > >a Check Engine light if it detects that the cat has gone bad.
: > >
: > >Jerry
: >
:
:
The catalyst monitor uses dual oxygen sensors
(O2S's) to monitor the efficiency of the converter. The
dual O2S's sensor strategy is based on the fact that
as a catalyst deteriorates, its oxygen storage capacity
and its efficiency are both reduced. By monitoring
the oxygen storage capacity of a catalyst, its efficiency
can be indirectly calculated. The upstream
O2S is used to detect the amount of oxygen in the
exhaust gas before the gas enters the catalytic converter.
The PCM calculates the A/F mixture from the
output of the O2S. A low voltage indicates high oxygen
content (lean mixture). A high voltage indicates a
low content of oxygen (rich mixture).
When the upstream O2S detects a lean condition,
there is an abundance of oxygen in the exhaust gas.
A functioning converter would store this oxygen so it
can use it for the oxidation of HC and CO. As the
converter absorbs the oxygen, there will be a lack of
oxygen downstream of the converter. The output of
the downstream O2S will indicate limited activity in
this condition.
As the converter loses the ability to store oxygen,
the condition can be detected from the behavior of
the downstream O2S. When the efficiency drops, no
chemical reaction takes place. This means the concentration
of oxygen will be the same downstream as
upstream. The output voltage of the downstream
O2S copies the voltage of the upstream sensor. The
only difference is a time lag (seen by the PCM)
between the switching of the O2S's.
To monitor the system, the number of lean-to-rich
switches of upstream and downstream O2S's is
counted. The ratio of downstream switches to
upstream switches is used to determine whether the
catalyst is operating properly. An effective catalyst
will have fewer downstream switches than it has
upstream switches i.e., a ratio closer to zero. For a
totally ineffective catalyst, this ratio will be one-toone,
indicating that no oxidation occurs in the device.
The system must be monitored so that when catalyst
efficiency deteriorates and exhaust emissions
increase to over the legal limit, the MIL will be illuminated.
--
Dave Milne, Scotland
'99 TJ 4.0 Sahara
"Jerry Bransford" <jerrypb@mecox.net> wrote in message
news:PS7fb.38240$gv5.27728@fed1read05...
: Why do I seem to recall that my '97 FSM says the downstream sensor is only
: there to monitor the cat, and that the upstream sensor checks and tells
the
: PCM how to adjust the injector's pulse duration for proper fuel mixture?
:
: Jerry
:
: --
: --
: Jerry Bransford
: To email, remove 'me' from my email address
: KC6TAY, PP-ASEL
: See the Geezer Jeep at
: http://members.***.net/jerrypb/
:
: "bllsht" <nospam@invaliddot.net> wrote in message
: news:4n0qnvg1k6p53k6f6r0n3a62i5jaju8d8d@4ax.com...
: > Actually, the PCM will use downstream O2 input to "fine tune" fuel trim
in
: > addition to monitoring the cat.
: >
: > The OP didn't say what engine he had, but there's a TSB for 4.0L engines
: > concerning decarbonizing the combustion chamber and revised valve
springs.
: >
: >
: >
: > In message <bvWeb.37369$gv5.16849@fed1read05>, "Jerry Bransford" wrote:
: >
: > >The downstream 02 sensor, unlike the upstream 02 sensor, has no ability
: to
: > >adjust the fuel mixture or for that matter, anything about how the
engine
: > >runs. Its sole function is to check the cat for proper function and
: display
: > >a Check Engine light if it detects that the cat has gone bad.
: > >
: > >Jerry
: >
:
:
10-05-2003, 06:58 AM
#20
Guest
Posts: n/a
Re: O2 sensor
From the FSM:
The catalyst monitor uses dual oxygen sensors
(O2S's) to monitor the efficiency of the converter. The
dual O2S's sensor strategy is based on the fact that
as a catalyst deteriorates, its oxygen storage capacity
and its efficiency are both reduced. By monitoring
the oxygen storage capacity of a catalyst, its efficiency
can be indirectly calculated. The upstream
O2S is used to detect the amount of oxygen in the
exhaust gas before the gas enters the catalytic converter.
The PCM calculates the A/F mixture from the
output of the O2S. A low voltage indicates high oxygen
content (lean mixture). A high voltage indicates a
low content of oxygen (rich mixture).
When the upstream O2S detects a lean condition,
there is an abundance of oxygen in the exhaust gas.
A functioning converter would store this oxygen so it
can use it for the oxidation of HC and CO. As the
converter absorbs the oxygen, there will be a lack of
oxygen downstream of the converter. The output of
the downstream O2S will indicate limited activity in
this condition.
As the converter loses the ability to store oxygen,
the condition can be detected from the behavior of
the downstream O2S. When the efficiency drops, no
chemical reaction takes place. This means the concentration
of oxygen will be the same downstream as
upstream. The output voltage of the downstream
O2S copies the voltage of the upstream sensor. The
only difference is a time lag (seen by the PCM)
between the switching of the O2S's.
To monitor the system, the number of lean-to-rich
switches of upstream and downstream O2S's is
counted. The ratio of downstream switches to
upstream switches is used to determine whether the
catalyst is operating properly. An effective catalyst
will have fewer downstream switches than it has
upstream switches i.e., a ratio closer to zero. For a
totally ineffective catalyst, this ratio will be one-toone,
indicating that no oxidation occurs in the device.
The system must be monitored so that when catalyst
efficiency deteriorates and exhaust emissions
increase to over the legal limit, the MIL will be illuminated.
--
Dave Milne, Scotland
'99 TJ 4.0 Sahara
"Jerry Bransford" <jerrypb@mecox.net> wrote in message
news:PS7fb.38240$gv5.27728@fed1read05...
: Why do I seem to recall that my '97 FSM says the downstream sensor is only
: there to monitor the cat, and that the upstream sensor checks and tells
the
: PCM how to adjust the injector's pulse duration for proper fuel mixture?
:
: Jerry
:
: --
: --
: Jerry Bransford
: To email, remove 'me' from my email address
: KC6TAY, PP-ASEL
: See the Geezer Jeep at
: http://members.***.net/jerrypb/
:
: "bllsht" <nospam@invaliddot.net> wrote in message
: news:4n0qnvg1k6p53k6f6r0n3a62i5jaju8d8d@4ax.com...
: > Actually, the PCM will use downstream O2 input to "fine tune" fuel trim
in
: > addition to monitoring the cat.
: >
: > The OP didn't say what engine he had, but there's a TSB for 4.0L engines
: > concerning decarbonizing the combustion chamber and revised valve
springs.
: >
: >
: >
: > In message <bvWeb.37369$gv5.16849@fed1read05>, "Jerry Bransford" wrote:
: >
: > >The downstream 02 sensor, unlike the upstream 02 sensor, has no ability
: to
: > >adjust the fuel mixture or for that matter, anything about how the
engine
: > >runs. Its sole function is to check the cat for proper function and
: display
: > >a Check Engine light if it detects that the cat has gone bad.
: > >
: > >Jerry
: >
:
:
The catalyst monitor uses dual oxygen sensors
(O2S's) to monitor the efficiency of the converter. The
dual O2S's sensor strategy is based on the fact that
as a catalyst deteriorates, its oxygen storage capacity
and its efficiency are both reduced. By monitoring
the oxygen storage capacity of a catalyst, its efficiency
can be indirectly calculated. The upstream
O2S is used to detect the amount of oxygen in the
exhaust gas before the gas enters the catalytic converter.
The PCM calculates the A/F mixture from the
output of the O2S. A low voltage indicates high oxygen
content (lean mixture). A high voltage indicates a
low content of oxygen (rich mixture).
When the upstream O2S detects a lean condition,
there is an abundance of oxygen in the exhaust gas.
A functioning converter would store this oxygen so it
can use it for the oxidation of HC and CO. As the
converter absorbs the oxygen, there will be a lack of
oxygen downstream of the converter. The output of
the downstream O2S will indicate limited activity in
this condition.
As the converter loses the ability to store oxygen,
the condition can be detected from the behavior of
the downstream O2S. When the efficiency drops, no
chemical reaction takes place. This means the concentration
of oxygen will be the same downstream as
upstream. The output voltage of the downstream
O2S copies the voltage of the upstream sensor. The
only difference is a time lag (seen by the PCM)
between the switching of the O2S's.
To monitor the system, the number of lean-to-rich
switches of upstream and downstream O2S's is
counted. The ratio of downstream switches to
upstream switches is used to determine whether the
catalyst is operating properly. An effective catalyst
will have fewer downstream switches than it has
upstream switches i.e., a ratio closer to zero. For a
totally ineffective catalyst, this ratio will be one-toone,
indicating that no oxidation occurs in the device.
The system must be monitored so that when catalyst
efficiency deteriorates and exhaust emissions
increase to over the legal limit, the MIL will be illuminated.
--
Dave Milne, Scotland
'99 TJ 4.0 Sahara
"Jerry Bransford" <jerrypb@mecox.net> wrote in message
news:PS7fb.38240$gv5.27728@fed1read05...
: Why do I seem to recall that my '97 FSM says the downstream sensor is only
: there to monitor the cat, and that the upstream sensor checks and tells
the
: PCM how to adjust the injector's pulse duration for proper fuel mixture?
:
: Jerry
:
: --
: --
: Jerry Bransford
: To email, remove 'me' from my email address
: KC6TAY, PP-ASEL
: See the Geezer Jeep at
: http://members.***.net/jerrypb/
:
: "bllsht" <nospam@invaliddot.net> wrote in message
: news:4n0qnvg1k6p53k6f6r0n3a62i5jaju8d8d@4ax.com...
: > Actually, the PCM will use downstream O2 input to "fine tune" fuel trim
in
: > addition to monitoring the cat.
: >
: > The OP didn't say what engine he had, but there's a TSB for 4.0L engines
: > concerning decarbonizing the combustion chamber and revised valve
springs.
: >
: >
: >
: > In message <bvWeb.37369$gv5.16849@fed1read05>, "Jerry Bransford" wrote:
: >
: > >The downstream 02 sensor, unlike the upstream 02 sensor, has no ability
: to
: > >adjust the fuel mixture or for that matter, anything about how the
engine
: > >runs. Its sole function is to check the cat for proper function and
: display
: > >a Check Engine light if it detects that the cat has gone bad.
: > >
: > >Jerry
: >
:
: