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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / November 2005Dodge 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: 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 Thanks, David BTW, car is a 97 The after cat sensor should switch about 1/2 the frequency of the pre cat sensor, and if the cat is working properly and there are no mixture problem the post cat sensor usually maintains about 450-650 and as you see the swing and rate of change is slower and less drastic than pre cat sensors. I don't see how you could fail without a check engine lite or a pending code at least, assuming the engine was at operating temp. Post back the limits for each gas. The post cat sensor looks richer because the cat is using exhaust stream o2 to function properly, by the way. >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 [quoted text clipped - 45 lines] > > David Hey Shep, thanks for the quick reply! There was no pending or stored code; light illuminates when it should (i.e. disconnect sensors and it will throw a code) Here are the max values HC CO NO 56 .51 443 15MPH 40 .49 730 25MPH Yeah the exahust is rich, hc's are usually raw fuel, gas contaminated oil, overloaded vapor cannister, engine misfire, all can cause this and the co also. Excessivey high fuel pressure here also, cat efficiency can be tested using an infrared thermo, temp at outlet of cat should be about 100 degrees or more than the inlet, but I don't see how this thing has no codes here. What is the long term fuel trim, should be -10 or more by the 4 gas readings? Your nox failed also, this is usually an egr problem. > Hey Shep, thanks for the quick reply! > [quoted text clipped - 7 lines] > 56 .51 443 15MPH > 40 .49 730 25MPH 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 Coolant temp approx 190F 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 Unfortunately, I did not make any logs before I made repairs. It looks like this car should pass, fuel trims are are little high, trying to pull some fuel out, check the cat as I said, make sure it is good and warmed up, change the oil if it's got some time on it. Looking at the map and fuel trims you will notice as the map goes down the fuel trims go up ( more fuel being removed), this shouldn't happen at a steady throttle/engine load. Map shouldn't drop from 19 to 12 on a flat road steady throttle. What units are these map readings, just a scale on the scope? > Unfortunately, I did not make any logs before I made repairs. I think the first high map readings were due to the fact I was making my way to 25MPH so the first 7 readings should probably be ignored as well as the last reading. The units are in inches Hg. Ok, that the explains what looked like an anomoly, other than what I have mentioned, I am out of ideas, good luck. BTW did you replace the pre cat sensor might give a try but, your hc's and co's don't indicate that to be a problem. >I think the first high map readings were due to the fact I was making > my way to 25MPH so the first 7 readings should probably be ignored as > well as the last reading. The units are in inches Hg. Did not replace the upstream because the readings look so good on it with the scope and the OBDII laptop. I think I will go get a pre test and at least compare the numbers and see where I am at. 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 for the input Shep... 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) Great, FYI, I am an emmisions inspector in NYS, ( day off today 6"of sno here)we do obd11 tests and tailpipe tests for pre 95's, you did a good job with this, just do some more research on the relationship between the readings of the pre and post cat sensors, there is a wealth of diagnostic parameters in understanding this thoroughly. > 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 [quoted text clipped - 10 lines] > most of the problem, now I just need to see about lowering the HC's > just a hair (and maybe the NO) I am actually a product manager for a consumer electronics company but by background is electrical engineering... I like working on my own cars as I have found I usually save a lot of money this way. I used to have a 78 Datsun 510 that I limped to 860,000 miles without ever taking it to a shop (before I got broadsided and they had to cut me out of it) I loved that car, I could fix just about anything on it. Thanks again for your help! Well, an update... Went and took the actual test and it failed again. Not very badly (4 or 5 PPM on HC). The NOX was much lower than before. Seeing as I have done all the repairs that got it close (and out of the 3 digits on HC), I decided to bite the bullet and get the cat tested; as was suspected, the cat was shot. I was there when the tech removed it from the vehicle, and pieces fell out when he handed it to me. Once he got the new one put on, he was nice enough to give me a free pre-test (I make friends easily (-: ) The new readings for HC are thru the floor and in the low single digits and all the rest of the readings were very good except for the NOX; it was a bit high. I retested the EGR and transducer, and they are operating correctly (still scratching my head, maybe carbon in the combustion chamber?) On a side note; last night I decided that I wanted to take the car for a nice long hard freeway drive before I got the cat put on so I could get myself some baseline numbers. I figured a San Bernardino to Cajon Summit (interstate 15) to Chiriaco Summit (interstate 10)was in order. I had no doubts the car would be able to do the Cajon Summit trip with little effort; I was a tad worried about the Chiriaco climb as that takes you from 70 ft below sea level to 2500 ft on a pretty good grade (it's known for killing cars) . I was amazed that my car was able to sustain the climb at 70MPH. The last time I tried climbing it a few years back, I had trouble keeping it above 55. I put on 312 miles last night in 4 hours just driving the freeways. After checking my mileage, I averaged 30MPG!!! My car has not gotten that since it was new. I forgot how much I like to drive when I am not sitting on the freeway stuck in traffic. Final update... IT PASSED THE TEST at the test only station! The rnumbers were lower than I have ever seen on the car (or any car I have owned for that matter) The NOX was 5 at 15MPH and 3 at 25MPH. The HC's were 7 at 25MPH and 9 at 15MPH. Thanks again for all the input! |
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