Dodge straus 2.4 strange O2S reading (I think)

I am having some problems with passing emission test and the only odd
thing I see while viewing the OBDII data on a laptop is that the
downstream O2 sensor seems to be seeing a rich condition (slow
switching between .57 to about .86) while the upstream O2 sensor is
giving me a nice fast switching .02 to about .7 sine wave.

I have replaced the O2 sensor and am still observing the same behavior.
Is this normal?

In my quest to correct my horribly failed emissions test, I have tested
and replaced the following:

Replaced:
IAC (motor seized about mid way)
DS O2S (probably did not need to)
Coolant temperature sensor (replaced because of erratic readings a
couple months back)
PCV valve
a couple old cracked vacuum lines


Tested and functioning correctly:
TPS
EGR
Evap system
vacuum system
fuel pressure/volume
compression

I also performed the normal tune up steps prior to the inspection. I
have not wanted to go back and have it tested again since I made the
repairs because the exhaust still smells rich to me.

The car does not and has never had any driveability problems and gets
around 23-25MPG.

Car has about 215K freeway miles on it but had a dealer installed
engine at 95K miles, and is well maintained.

Here are the results of the emissions test (California)

Test RPM %CO2 O2 HC CO NO
15 MPH 1858 14 0 139 1.14 659
25 MPH 1915 13.6 0 165 1.47 822

Any help is appreciated

 

BTW, car is a 97

 

The down stream 02 sensor is supposed to have a slow curve, that is telling
you that the cat is working,
If the downstream was the same as the upstream curve that would give you a
catalytic converter fault code

Glenn Beasley
Chrysler Tech

 

From your description, it sounds like it. First, the speed of the
switching has nothing to do with rich vs. lean. The fact that you're
switching back and forth between low and high says things are
behaving. You say it's a "nice fast" switching on the upstream
sensor; I don't know either what you mean by "nice fast" nor what
the spec is on that,but at a first glance it sounds OK.

The much slower switching downstream is also OK. The convertor
stores some oxygen when getting a lean mixture and burns it when
getting a rich one, so the downstream sensor doesn't switch nearly as
fast as the upstream. Somewhere in the '95 Neon FSM (I know, different
car, but the principle will hold) it describes this as the test for a
good catalyst: if the downstream is switching as fast asthe upstream,
it means the cat isn't doing anything.

Not seeing anything obvious in the rest of the post...

 

Hey Glenn, thanks for the quick reply. I know that the slow switching
is normal, I am just concerned with the .86 volt reading and the rich
exhaust smell... Everything I have read thus far tells me that I should
see a slow switching response but that it should be closer to the
center line mark (.47). I guess I should just go have the retest done
and cross my fingers after fixing what I have thus far.

 

I'm sorry -- when you said slow switching I didn't notice the voltages
you were talking about. If it's never getting down to .5 V, then it's
not switching! Now it does sound like you're running rich for some
reason... since the upstream sensor is switching, I wonder about a
leaky injector? Since you're reading this with a laptop, I haven't
asked about stored codes...

 

Ran the above gas readings thru a Lambda calculator, the exhaust
smells rich because it is rich. Find and correct the cause of
the rich condition. If your laptop software gives you fuel trim
numbers, they can help you decide if you're on the right track.
Leaking injectors, skewed O2 sensor, evap/purge problems, MAF
problem, PCV valve problem, all areas that can contribute to over
fueling.

 

Unfortunately I can only log 6 values at once. These readings were
taken over about 50 seconds on a flat road at 25MPH (cruise control set

for stability) at approximately 850ft elevation with outside
temperature in the 60's.

Sample Rate Setting=0.100
Start Time:8:26:23 AM
Date of Log:10/25/2005


MAP USO2S DSO2S TPS% RPM LT FT

19.5 0.255 0.745 20 2058.25 -1.6
19.5 0.175 0.745 20 2006.75 -2.3
18.6 0.155 0.785 19 2007.25 -3.1
18.6 0.12 0.685 19 2029.25 -3.9
17.1 0.335 0.765 18 2018 -3.9
16.2 0.665 0.705 18 2031.5 -3.1
17.4 0.1 0.725 17 2017.75 -4.7
13.3 0.53 0.785 16 1987 -6.3
12.7 0.725 0.705 16 1986.5 -7
11.5 0.1 0.235 14 1934 -7
12.1 0.175 0.63 14 1926 -7
12.1 0.55 0.685 14 1916.75 -6.3
11.5 0.665 0.785 14 1915.25 -6.3
12.1 0.685 0.765 14 1905.5 -6.3
11.5 0.175 0.745 14 1900.25 -6.3
12.1 0.12 0.765 14 1904.5 -6.3
11.5 0.705 0.765 14 1884.5 -6.3
11.2 0.705 0.745 14 1880.5 -5.5
11.5 0.685 0.765 14 1880.75 -5.5
11.2 0.645 0.745 14 1870.5 -5.5
11.5 0.1 0.685 14 1880.5 -5.5
12.1 0.12 0.745 14 1875 -5.5
12.1 0.215 0.745 14 1878 -5.5
11.5 0.1 0.725 14 1878.75 -5.5
11.5 0.295 0.745 14 1877.25 -5.5
11.2 0.57 0.725 14 1871 -5.5
11.8 0.59 0.725 14 1877.75 -5.5
11.5 0.12 0.765 14 1887.25 -5.5
11.8 0.49 0.765 14 1880.5 -5.5
11.5 0.665 0.725 14 1883.5 -5.5
11.5 0.55 0.705 14 1876 -4.7
12.1 0.135 0.745 14 1888 -4.7
11.2 0.175 0.765 13 1845.25 -4.7
10 0.12 0.765 14 1842 -5.5
11.2 0.1 0.665 14 1831.5 -5.5
10.3 0.12 0.725 14 1876.5 -4.7
11.5 0.12 0.725 18 1998.75 -5.5
15.6 0.725 0.785 16 1958.5 0

 

Dave long and short term adaptive memory will tell you if you have a
problem. Are you able to view the fuel cells with lap top? And what year
vehicle is this?

 

It is a 97

Fuel cells? I can view long term and short term trim... Long term is
posted above in the last column.

 

If that is long term addaptive fuel memory to the right and the highest
number is -7 I dont see where there is a rich running problem or a lean
running problem

 

Well, I guess maybe one of the fixes I did above maybe fixed the
problem... I guess I should just bite the bullet and take it in and see
if it passes. Wish me luck (-:

 

Well, GOOD NEWS! I took it for a pre test and it PASSED! The HC's are
still a little high so I want to bring them down just a hair as they
were right at the limit. The tech said it may be because it idled a
little too long while they sorted out a proble with the computer.

Here are the new numbers:

Test RPM %CO2 %O2 HC %CO NO
15MPH 1850 15.0 0.1 55 0.14 430
25MPH 1890 15.0 0.1 40 0.14 417

Thank you everyone for the input... I guess the repairs I made took
care of most of the problem, now I just need to see about lowering the
HC's just a hair (and maybe the NO)

 

I figured it had something to do with loading at idle before the test was
done. But according to your adaptives, your vehicle is not running rich. if
those negative numbers go into the -10's or +10's then you may be starting
to have a problem

 

no is a little high i would venture to gusee the cat is broke inside

 

me either
bang on the cat and see if it rattles

 

No way to know since he only posted the long term trims.
What if that -7 LTFT was accompanied by a -5 STFT?

 

Since the LT trim actually increased from the low of -7, that obviously wasn't
the case.

 

Ok, I give up what if?

 

Would a -12 fuel trim cause you to consider that the engine was
running rich?
Not huge rich, but as rich as the Lambda calculation indicates?