Interesting (textbook I guess) effects of a bad O2 sensor

Hi All,

I thought I would post the output of my OTC Monitor 4000E with the
Pathfinder 97
cartridge, along with some comments, since it's such a textbook case of a
bad O2
sensor. This is from my 1995 Chrysler Town & Country minivan with 3.8L
engine.
The '95 T&C is a pre-OBD-II vehicle, so I have to use a scantool that is
designed for it.
The scantool cartridge I have is the last cartridge year that OTC made that
will work in the
Monitor 4000E The 95 T&C has 2 vehicle diagnostic ports, one in the engine
bay
and one under the dash, the one in the engine bay talks to the engine
computer, the one
under the dash talks to the transmission computer. I have the adapters for
both ports.

As part of the registration renewal here you have to go through emissions
inspection.
I first ran my van though 12/31/08 and it failed with an idle reading of:

HC 519ppm
CO 9.2721%
CO2 was at 8.5%

There was no check engine light visible.

I then waited for a weekend that wasn't snowing or raining and replaced the
spark plugs
and spark plug wires - the old plugs had worn
to a gap that was almost double the factory spec and the plug wires were the
original
wires - and when you take the time to do plugs in that vehicle, (the back
ones are not easy
to get to, I put the car up on jackstands and used a creeper to get at the
plugs
from the bottom) you might as well do the wires. I replaced the plugs with
Autolite
Platinum that I bought from Walmart (yes, believe it or not they carried
them)

I then took the van back through emissions on 1/24 and it failed with an
idle reading of:

HC 477ppm
CO 10.1685%
CO2 7.9%

Ok, so now the easy/cheap/quick fixes were done it was time to break out the
scantool
and do some real diagnostics.

I warmed up the van and first pulled for any stored code and came up with
code 51 which
is a fuel/air mixture out of range problem. I then ran a printout of
parameters from the
scantool and got this( it looks best in a non-proportional font):


CHRYSLER 1995 3.3/3.8L SFI
----- REVIEW CODES -----

----- NUMBER OF CODES -----
01
51 O2 F/A SYS LEAN

----- PRINTING COMPLETE -----


CHRYSLER 1995 3.3/3.8L SFI

FAULT CODES: 51

-- BASIC INFORMATION BLOCK --
ENGINE COOLANT TEMP 199 F
ENGINE COOLANT SEN V 2.42 V
IDLE RPM X 10 075
INJ PULSE WIDTH 03.4 MS
LOOP STATUS CLSD
MAP 09.4 IHG
MAP VOLTS 1.18 V
OXYGEN BANK1 SENSOR1 0.00 V
ENGINE RPM 0747
THROT POS SENS VOLTS 0.64 V
TP SENSOR MINIMUM 0.64 V

-- ENGINE INFORMATION BLOCK --
ADAPTIVE FACTOR #1 +06 %
AIS/IAC STEPS 008
BARO PRESSURE 30.6 IHG
BATTERY TEMP 066 F
BATTERY VOLTS 13.8 V
CHARG SYS TARG VOLTS 13.8 V
CAM POSITION STATUS YES
CRANK POS STATUS YES
DESIRED AIS STEPS 008
ELECTRONIC ADV/RET 019 DEG
KNOCK ACTIVE NO
KNOCK SENSOR 1 VOLTS 0.00 V
VACUUM 21 IHG
VEHICLE SPEED SENS 000 MPH

-- MISC. VEHICLE DATA INFO. --
CRUISE CONTROL DIS
CRUISE CNTROL CUTOUT CRSW
CRUISE SET SPEED 000 MPH
CRUISE CONTRL STATUS CRSW
CRUISE CNTRL SWITCH 0.00 V
VEHICLE THEFT ALARM FUEL

------ PRINTING COMPLETE ------

Well, now this was strange - 0v from the O2 sensor? In case
this was a fluke I shut down the engine, then cleared the stored
error codes and got this:

CHRYSLER 1995 3.3/3.8L SFI

---GUIDED PATH STATUS----
Complete
Intermittent Code
Detected

------FAULT CODES-------

----- REVIEW CODES -----
NO CODES

--OUT OF RANGE SENSORS--
Number of sensors 0



------ PRINTING COMPLETE ------


CHRYSLER 1995 3.3/3.8L SFI

FAULT CODES: NO

-- BASIC INFORMATION BLOCK --
ENGINE COOLANT TEMP 217 F
ENGINE COOLANT SEN V 2.06 V
IDLE RPM X 10 075
INJ PULSE WIDTH 15.6 MS
LOOP STATUS OPEN
MAP 26.2 IHG
MAP VOLTS 4.00 V
OXYGEN BANK1 SENSOR1 0.22 V
ENGINE RPM 0000
THROT POS SENS VOLTS 0.66 V
TP SENSOR MINIMUM 0.72 V

-- ENGINE INFORMATION BLOCK --
ADAPTIVE FACTOR #1 +24 %
AIS/IAC STEPS 036
BARO PRESSURE 30.6 IHG
BATTERY TEMP 062 F
BATTERY VOLTS 11.9 V
CHARG SYS TARG VOLTS 13.9 V
CAM POSITION STATUS NO
CRANK POS STATUS NO
DESIRED AIS STEPS 036
ELECTRONIC ADV/RET 018 DEG
KNOCK ACTIVE NO
KNOCK SENSOR 1 VOLTS 0.00 V
VACUUM 04 IHG
VEHICLE SPEED SENS 000 MPH

-- MISC. VEHICLE DATA INFO. --
CRUISE CONTROL DIS
CRUISE CNTROL CUTOUT CRSW
CRUISE SET SPEED 000 MPH
CRUISE CONTRL STATUS CRSW
CRUISE CNTRL SWITCH 0.00 V
VEHICLE THEFT ALARM FUEL

------ PRINTING COMPLETE ------


Ok, that's a bit more normal - there's the voltage from the O2
sensor. I started up the engine and started running some more
printouts:

CHRYSLER 1995 3.3/3.8L SFI

FAULT CODES: NO

-- BASIC INFORMATION BLOCK --
ENGINE COOLANT TEMP 213 F
ENGINE COOLANT SEN V 2.16 V
IDLE RPM X 10 080
INJ PULSE WIDTH 03.5 MS
LOOP STATUS OPEN
MAP 09.4 IHG
MAP VOLTS 1.18 V
OXYGEN BANK1 SENSOR1 0.22 V
ENGINE RPM 0843
THROT POS SENS VOLTS 0.64 V
TP SENSOR MINIMUM 0.66 V

-- ENGINE INFORMATION BLOCK --
ADAPTIVE FACTOR #1 +24 %
AIS/IAC STEPS 016
BARO PRESSURE 30.6 IHG
BATTERY TEMP 062 F
BATTERY VOLTS 13.8 V
CHARG SYS TARG VOLTS 13.9 V
CAM POSITION STATUS YES
CRANK POS STATUS YES
DESIRED AIS STEPS 016
ELECTRONIC ADV/RET 015 DEG
KNOCK ACTIVE NO
KNOCK SENSOR 1 VOLTS 0.00 V
VACUUM 21 IHG
VEHICLE SPEED SENS 000 MPH

-- MISC. VEHICLE DATA INFO. --
CRUISE CONTROL DIS
CRUISE CNTROL CUTOUT CRSW
CRUISE SET SPEED 000 MPH
CRUISE CONTRL STATUS CRSW
CRUISE CNTRL SWITCH 0.00 V
VEHICLE THEFT ALARM FUEL

------ PRINTING COMPLETE ------






CHRYSLER 1995 3.3/3.8L SFI

FAULT CODES: NO

-- BASIC INFORMATION BLOCK --
ENGINE COOLANT TEMP 206 F
ENGINE COOLANT SEN V 2.30 V
IDLE RPM X 10 075
INJ PULSE WIDTH 04.6 MS
LOOP STATUS CLSD
MAP 10.2 IHG
MAP VOLTS 1.30 V
OXYGEN BANK1 SENSOR1 0.04 V
ENGINE RPM 0745
THROT POS SENS VOLTS 0.66 V
TP SENSOR MINIMUM 0.66 V

-- ENGINE INFORMATION BLOCK --
ADAPTIVE FACTOR #1 +24 %
AIS/IAC STEPS 016
BARO PRESSURE 30.6 IHG
BATTERY TEMP 062 F
BATTERY VOLTS 13.8 V
CHARG SYS TARG VOLTS 13.9 V
CAM POSITION STATUS YES
CRANK POS STATUS YES
DESIRED AIS STEPS 016
ELECTRONIC ADV/RET 018 DEG
KNOCK ACTIVE NO
KNOCK SENSOR 1 VOLTS 0.00 V
VACUUM 20 IHG
VEHICLE SPEED SENS 000 MPH

-- MISC. VEHICLE DATA INFO. --
CRUISE CONTROL DIS
CRUISE CNTROL CUTOUT CRSW
CRUISE SET SPEED 000 MPH
CRUISE CONTRL STATUS CRSW
CRUISE CNTRL SWITCH 0.00 V
VEHICLE THEFT ALARM FUEL

------ PRINTING COMPLETE ------


Ok, so notice something. The O2 sensor voltage is
starting to fall. The Chrysler O2 sensor is a heated
sensor - when engine is off, the sensor heater is off -
when the engine is started the sensor heater starts warming
it up. So as the sensor was getting warmer, it's voltage
output was getting lower.

I continued running some more printouts, and
as you can see from the following 4 printouts, the
O2 sensor voltage remained at zero.


CHRYSLER 1995 3.3/3.8L SFI

FAULT CODES: NO

-- BASIC INFORMATION BLOCK --
ENGINE COOLANT TEMP 206 F
ENGINE COOLANT SEN V 2.22 V
IDLE RPM X 10 075
INJ PULSE WIDTH 04.4 MS
LOOP STATUS CLSD
MAP 09.8 IHG
MAP VOLTS 1.26 V
OXYGEN BANK1 SENSOR1 0.00 V
ENGINE RPM 0780
THROT POS SENS VOLTS 0.66 V
TP SENSOR MINIMUM 0.66 V

-- ENGINE INFORMATION BLOCK --
ADAPTIVE FACTOR #1 +24 %
AIS/IAC STEPS 014
BARO PRESSURE 30.6 IHG
BATTERY TEMP 062 F
BATTERY VOLTS 13.8 V
CHARG SYS TARG VOLTS 13.9 V
CAM POSITION STATUS YES
CRANK POS STATUS YES
DESIRED AIS STEPS 014
ELECTRONIC ADV/RET 013 DEG
KNOCK ACTIVE NO
KNOCK SENSOR 1 VOLTS 0.00 V
VACUUM 21 IHG
VEHICLE SPEED SENS 000 MPH

-- MISC. VEHICLE DATA INFO. --
CRUISE CONTROL DIS
CRUISE CNTROL CUTOUT CRSW
CRUISE SET SPEED 000 MPH
CRUISE CONTRL STATUS CRSW
CRUISE CNTRL SWITCH 0.00 V
VEHICLE THEFT ALARM FUEL

------ PRINTING COMPLETE ------






CHRYSLER 1995 3.3/3.8L SFI

FAULT CODES: NO

-- BASIC INFORMATION BLOCK --
ENGINE COOLANT TEMP 208 F
ENGINE COOLANT SEN V 2.18 V
IDLE RPM X 10 075
INJ PULSE WIDTH 03.5 MS
LOOP STATUS CLSD
MAP 09.4 IHG
MAP VOLTS 1.18 V
OXYGEN BANK1 SENSOR1 0.00 V
ENGINE RPM 0720
THROT POS SENS VOLTS 0.66 V
TP SENSOR MINIMUM 0.66 V

-- ENGINE INFORMATION BLOCK --
ADAPTIVE FACTOR #1 +06 %
AIS/IAC STEPS 008
BARO PRESSURE 30.6 IHG
BATTERY TEMP 060 F
BATTERY VOLTS 13.8 V
CHARG SYS TARG VOLTS 13.9 V
CAM POSITION STATUS YES
CRANK POS STATUS YES
DESIRED AIS STEPS 008
ELECTRONIC ADV/RET 017 DEG
KNOCK ACTIVE NO
KNOCK SENSOR 1 VOLTS 0.00 V
VACUUM 21 IHG
VEHICLE SPEED SENS 000 MPH

-- MISC. VEHICLE DATA INFO. --
CRUISE CONTROL DIS
CRUISE CNTROL CUTOUT CRSW
CRUISE SET SPEED 000 MPH
CRUISE CONTRL STATUS CRSW
CRUISE CNTRL SWITCH 0.00 V
VEHICLE THEFT ALARM FUEL

------ PRINTING COMPLETE ------






CHRYSLER 1995 3.3/3.8L SFI

FAULT CODES: NO

-- BASIC INFORMATION BLOCK --
ENGINE COOLANT TEMP 210 F
ENGINE COOLANT SEN V 2.16 V
IDLE RPM X 10 075
INJ PULSE WIDTH 03.8 MS
LOOP STATUS CLSD
MAP 09.5 IHG
MAP VOLTS 1.20 V
OXYGEN BANK1 SENSOR1 0.00 V
ENGINE RPM 0726
THROT POS SENS VOLTS 0.66 V
TP SENSOR MINIMUM 0.64 V

-- ENGINE INFORMATION BLOCK --
ADAPTIVE FACTOR #1 +13 %
AIS/IAC STEPS 010
BARO PRESSURE 30.6 IHG
BATTERY TEMP 062 F
BATTERY VOLTS 13.9 V
CHARG SYS TARG VOLTS 13.9 V
CAM POSITION STATUS YES
CRANK POS STATUS YES
DESIRED AIS STEPS 010
ELECTRONIC ADV/RET 017 DEG
KNOCK ACTIVE NO
KNOCK SENSOR 1 VOLTS 0.00 V
VACUUM 21 IHG
VEHICLE SPEED SENS 000 MPH

-- MISC. VEHICLE DATA INFO. --
CRUISE CONTROL DIS
CRUISE CNTROL CUTOUT CRSW
CRUISE SET SPEED 000 MPH
CRUISE CONTRL STATUS CRSW
CRUISE CNTRL SWITCH 0.00 V
VEHICLE THEFT ALARM FUEL

------ PRINTING COMPLETE ------






CHRYSLER 1995 3.3/3.8L SFI

FAULT CODES: NO

-- BASIC INFORMATION BLOCK --
ENGINE COOLANT TEMP 217 F
ENGINE COOLANT SEN V 2.00 V
IDLE RPM X 10 075
INJ PULSE WIDTH 03.5 MS
LOOP STATUS CLSD
MAP 09.3 IHG
MAP VOLTS 1.16 V
OXYGEN BANK1 SENSOR1 0.00 V
ENGINE RPM 0750
THROT POS SENS VOLTS 0.64 V
TP SENSOR MINIMUM 0.64 V

-- ENGINE INFORMATION BLOCK --
ADAPTIVE FACTOR #1 +09 %
AIS/IAC STEPS 009
BARO PRESSURE 30.6 IHG
BATTERY TEMP 062 F
BATTERY VOLTS 13.8 V
CHARG SYS TARG VOLTS 13.9 V
CAM POSITION STATUS YES
CRANK POS STATUS YES
DESIRED AIS STEPS 009
ELECTRONIC ADV/RET 021 DEG
KNOCK ACTIVE NO
KNOCK SENSOR 1 VOLTS 0.00 V
VACUUM 21 IHG
VEHICLE SPEED SENS 000 MPH

-- MISC. VEHICLE DATA INFO. --
CRUISE CONTROL DIS
CRUISE CNTROL CUTOUT CRSW
CRUISE SET SPEED 000 MPH
CRUISE CONTRL STATUS CRSW
CRUISE CNTRL SWITCH 0.00 V
VEHICLE THEFT ALARM FUEL

------ PRINTING COMPLETE ------


Ok, so the O2 sensor must be faulty. So I bought
a new sensor (Denso part 234-4210) and replaced it
2/7/09 and got these readouts on a warm engine:


CHRYSLER 1995 3.3/3.8L SFI

FAULT CODES: NO

-- BASIC INFORMATION BLOCK --
ENGINE COOLANT TEMP 212 F
ENGINE COOLANT SEN V 2.16 V
IDLE RPM X 10 075
INJ PULSE WIDTH 02.8 MS
LOOP STATUS CLSD
MAP 09.4 IHG
MAP VOLTS 1.18 V
OXYGEN BANK1 SENSOR1 0.10 V
ENGINE RPM 0737
THROT POS SENS VOLTS 0.66 V
TP SENSOR MINIMUM 0.66 V

-- ENGINE INFORMATION BLOCK --
ADAPTIVE FACTOR #1 +06 %
AIS/IAC STEPS 008
BARO PRESSURE 30.2 IHG
BATTERY TEMP 055 F
BATTERY VOLTS 13.9 V
CHARG SYS TARG VOLTS 14.0 V
CAM POSITION STATUS YES
CRANK POS STATUS YES
DESIRED AIS STEPS 008
ELECTRONIC ADV/RET 018 DEG
KNOCK ACTIVE NO
KNOCK SENSOR 1 VOLTS 0.00 V
VACUUM 21 IHG
VEHICLE SPEED SENS 000 MPH

-- MISC. VEHICLE DATA INFO. --
CRUISE CONTROL DIS
CRUISE CNTROL CUTOUT CRSW
CRUISE SET SPEED 000 MPH
CRUISE CONTRL STATUS CRSW
CRUISE CNTRL SWITCH 0.00 V
VEHICLE THEFT ALARM FUEL

------ PRINTING COMPLETE ------






CHRYSLER 1995 3.3/3.8L SFI

FAULT CODES: NO

-- BASIC INFORMATION BLOCK --
ENGINE COOLANT TEMP 212 F
ENGINE COOLANT SEN V 2.16 V
IDLE RPM X 10 075
INJ PULSE WIDTH 02.7 MS
LOOP STATUS CLSD
MAP 09.3 IHG
MAP VOLTS 1.16 V
OXYGEN BANK1 SENSOR1 0.80 V
ENGINE RPM 0755
THROT POS SENS VOLTS 0.66 V
TP SENSOR MINIMUM 0.66 V

-- ENGINE INFORMATION BLOCK --
ADAPTIVE FACTOR #1 +06 %
AIS/IAC STEPS 008
BARO PRESSURE 30.2 IHG
BATTERY TEMP 055 F
BATTERY VOLTS 13.9 V
CHARG SYS TARG VOLTS 14.0 V
CAM POSITION STATUS YES
CRANK POS STATUS YES
DESIRED AIS STEPS 008
ELECTRONIC ADV/RET 019 DEG
KNOCK ACTIVE NO
KNOCK SENSOR 1 VOLTS 0.00 V
VACUUM 21 IHG
VEHICLE SPEED SENS 000 MPH

-- MISC. VEHICLE DATA INFO. --
CRUISE CONTROL DIS
CRUISE CNTROL CUTOUT CRSW
CRUISE SET SPEED 000 MPH
CRUISE CONTRL STATUS CRSW
CRUISE CNTRL SWITCH 0.00 V
VEHICLE THEFT ALARM FUEL

------ PRINTING COMPLETE ------

Now that's more like it - the O2 sensor voltage is
swinging between .1 and .8, and it's doing it every
2-3 seconds.

I also am now seeing the RICH and LEAN lights
on the scantool alternating back and forth.

And notice something else - the injector pulse width
is about half what it was with the faulty O2 sensor - that
is why the engine failed previously, the injectors were
just flooding the engine with fuel.

I will be taking the van through emissions on Tuesday, and
my hope is that the catalytic converter has not gotten plugged
up with carbon and is still working.

Ted

 

Not that ignition repairs weren't needed, but with CO at 9%, you're
looking at a rich condition. As you found out, ignition repairs won't
fix that. *Generally*, high CO indicates a mixture problem. High HC
would indicate ignition problems. You have both high HC and CO. Here,
the excess fuel that's not being burned is causing the high HC.

The low CO2 number indicates poor combustion, and the cat not working.
The cat not working would be expected with a mixture that rich. To be
efficient at oxidation process, a cat needs a near stoichiometric
mixture (14.7:1). Your numbers are nowhere near that.

My experience has been that a cat converter is more likely to survive
a rich condition than a lean or misfire condition.