careldo Posted February 25, 2004 Report Share Posted February 25, 2004 hey guys, trying to diagnose a bad exhaust smell--smells like kinda tar mixed with gas ---anyways brought up the data for the 02 sensors but not sure what i should be looking for right now i am getting fluctauting reference voltages between .57 volts and .78 volts and my counts are fluctauting something like 0 to 7 then to 5 back to o then to 3 and so on so what does this mean normal or not? thanks for any info Link to comment Share on other sites More sharing options...
Dloch Posted February 25, 2004 Report Share Posted February 25, 2004 hey guys,trying to diagnose a bad exhaust smell--smells like kinda tar mixed with gas ---anyways brought up the data for the 02 sensors but not sure what i should be looking for right now i am getting fluctauting reference voltages between .57 volts and .78 volts and my counts are fluctauting something like 0 to 7 then to 5 back to o then to 3 and so on so what does this mean normal or not? thanks for any info Are you getting any codes? Dennis Link to comment Share on other sites More sharing options...
careldo Posted February 25, 2004 Author Report Share Posted February 25, 2004 no codes Link to comment Share on other sites More sharing options...
Dloch Posted February 25, 2004 Report Share Posted February 25, 2004 The voltage level will normally cycle up and down, that is normal. The PCM will throw a code if it's not happy with what the O2 sensor is reporting. It could be the cat converter. Dennis Link to comment Share on other sites More sharing options...
careldo Posted February 25, 2004 Author Report Share Posted February 25, 2004 o.k thanks so let me ask how does one check a cat? careldo Link to comment Share on other sites More sharing options...
KevinW Posted February 25, 2004 Report Share Posted February 25, 2004 The catalytic converter could be producing a pungent odour (hydrogen sulphide) as a result of a mixture problem or fuel with a high sulphur content. What are the right and left block learn (B/L) values? If the O2 sensor voltage never drops below 0.57, something is wrong. ___________________________________________________ Link to comment Share on other sites More sharing options...
Dloch Posted February 25, 2004 Report Share Posted February 25, 2004 Where are you getting the O2 sensors voltages from? I agree with KevinW about the voltage not falling below .57. The BLM's should be shifted if that's the case, but, why hasn't the car throw a code for O2 voltage high? Unless the PCM wasn't quite that smart back then. Dennis Link to comment Share on other sites More sharing options...
careldo Posted February 26, 2004 Author Report Share Posted February 26, 2004 guys, i beleive the pcm won't throw a code unless voltage remains at a certain value for a predetermined time. I am getting my voltage values from the pcm-monitoring data if my memory serves me right id 34 and id 35 Kevin i am not sure where to get the block learn values you are mentioning but i will have a look in my manual and see if i can get thoses. thanks a bunch! Link to comment Share on other sites More sharing options...
careldo Posted February 26, 2004 Author Report Share Posted February 26, 2004 guys, picked up the block learn values here's what i got left 119 and right 121 from what i gather the pcm is trying to lean out the fuel as the 02 sensors are showing a rich condition.The values should be around 128 as per the manual.Now i have rechecked the voltage values and they are occaisionally falling below refernce voltage not as wrote earlier ,my mistake. Now here's were it gets a bit weird, according to my manual the cross counts should be 3 or greater(cross counts are the number of times the voltage crosses the reference voltage per second) this does not consistently stay above that.So my best semi-educated quess is that the 02 sensors are getting lazy and should be replaced or cleaned of any contamenants. Anyone agree or disagree? careldo Link to comment Share on other sites More sharing options...
loucar1 Posted February 26, 2004 Report Share Posted February 26, 2004 I think you are correct I would replace them both...not sure you can clean o2 sensors Lou 94 Seville STS Link to comment Share on other sites More sharing options...
KevinW Posted February 26, 2004 Report Share Posted February 26, 2004 picked up the block learn values here's what i got left 119 and right 121 from what i gather the pcm is trying to lean out the fuel as the 02 sensors are showing a rich condition.The values should be around 128 as per the manual. 128 is a theoretically ideal condition. There will always be some variance unless the values are locked at 128 under some open loop conditions. 119 is well within the acceptable range for fuel control; it suggests that a bit more fuel is being delivered than expected, or actual engine airflow is less than the calculated value, or the oxygen sensor voltage is biased high. The reported cross-counts are not definitive, but if the sensors have seen a lot of use and your fuel mileage isn't what it used to be, it wouldn't hurt to replace them before the diagnostic code is triggered. How about performing a cylinder balance test? ___________________________________________________ Link to comment Share on other sites More sharing options...
careldo Posted February 26, 2004 Author Report Share Posted February 26, 2004 thanks, kevin i will do a balance test this weekend and also change both 02 sensors and report back results Link to comment Share on other sites More sharing options...
Dloch Posted February 26, 2004 Report Share Posted February 26, 2004 128 is a theoretically ideal condition. There will always be some variance unless the values are locked at 128 under some open loop conditions. 119 is well within the acceptable range for fuel control; it suggests that a bit more fuel is being delivered than expected, or actual engine airflow is less than the calculated value, or the oxygen sensor voltage is biased high. The reported cross-counts are not definitive, but if the sensors have seen a lot of use and your fuel mileage isn't what it used to be, it wouldn't hurt to replace them before the diagnostic code is triggered. How about performing a cylinder balance test? The BLM's just provide an indication of what the PCM is doing with regards to adding of subtracting fuel based on the O2 sensor readings. Where it really comes into play is if you are tuning your car/PCM for changes you have made to the engine. When you go to wide open throttle, WOT, it will offset the fuel tables by the number that the BLM is off of 128. The PCM doesn't use the O2 sensors at WOT, it goes into speed density mode. Maybe I should qualify that statement, that is what the PCM in my Impala SS does. At WOT it looks at the programmed fuel tables (VE) that will be looking at TPS vs MAP vs RPM. Then there are a number of other offsets that are either added of subtracted based on other variables, like power enrichment that is adding or subtracting based on RPM. This can get very confusing, which means you can really screw something up if you changing numbers in the wrong areas. Some or a small offset is not a major problem, a large offset is, especially if you are boosting a motor and you are subtracting fuel... not good. Dennis Link to comment Share on other sites More sharing options...
KevinW Posted February 26, 2004 Report Share Posted February 26, 2004 Where it really comes into play is if you are tuning your car/PCM for changes you have made to the engine. I think the fuel trims were intended to be a diagnostic aid. If they wanted us playing with things, we'd be able to download the source code. When you go to wide open throttle, WOT, it will offset the fuel tables by the number that the BLM is off of 128. The PCM doesn't use the O2 sensors at WOT, it goes into speed density mode. The WOT fueling is corrected ONLY if the BLMs are greater than 128. In other words, if the PCM finds that it is having to add fuel (above the expected amount) during part throttle operation, it will add a similar percentage during power enrichment. This is to minimise the chance of lean operation under heavy loads. Speed Density refers to a fuel control strategy that estimates the quantity of air entering a engine based on temperature-compensated look-up values for a given engine RPM and manifold air pressure. Open Loop refers to the mode of operation where the PCM does not utilise input from the oxygen sensor(s), such as during warm-up, or WOT enrichment. Maybe I should qualify that statement, that is what the PCM in my Impala SS does. At WOT it looks at the programmed fuel tables (VE) that will be looking at TPS vs MAP vs RPM. Assuming your Impala SS has an LT1, the WOT fueling is not dependent on the Volumetric Efficiency tables, assuming your MAF sensor is connected and functioning. ___________________________________________________ Link to comment Share on other sites More sharing options...
Dloch Posted February 26, 2004 Report Share Posted February 26, 2004 Kevin, It does have an LT1, Just curious what are you programming LT1's with? Dennis Link to comment Share on other sites More sharing options...
KevinW Posted February 27, 2004 Report Share Posted February 27, 2004 I use Tunercat and a hex editor in the case of my Fleetwood. ___________________________________________________ Link to comment Share on other sites More sharing options...
Dloch Posted February 27, 2004 Report Share Posted February 27, 2004 Done many LT1's? Dennis Link to comment Share on other sites More sharing options...
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