Dodge straus 2.4 strange O2S reading (I think)

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 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?