Odd AFR behavior while SD tuning
03-27-2006, 03:31 PM
#1
Odd AFR behavior while SD tuning I decided to go back over the SD tune after making further idle adjustments. With the MAF enabled, my reported AFR was in the low-to-mid 15's. So I decided to read up on the updated SD tune online help over the last few releases (disabling closed loop, for instance). In the previous scans, I was using 0-5V=10-20AFR and the default LM1 PID.
To get more resolution, I followed Meents setup by using 0-5V=11-17AFR, and using a custom AFR PID (Volts/.833+11). Almost all of the cells are either hanging right around 14.7-15, or are at 16.9 (mostly at WOT). I double checked all the tables and according to the docs they are right on. Now, I did start with my previous SD tune done months ago under different conditions instead of adding 15% across the board.
If the 14.7 is accurate at idle and cruise, I presume it's accurate at 16.9 as well. So if I trust this, then my VE values are peaking at 115-120 at WOT and I just don't trust that I'm running this lean. Being I'm N/A, this really seems way out there. How would an exhaust leak behave on the wideband?
I compared the AFR reported on the LM-1 to that reported in Logworks 1.1, and it looks right on. HPT appears to be reading the same as the LM-1 display, albeit much faster screen updates. I loaded v1.42 of the LM-1 firmware a few weeks ago as well as Logworks 2.0, but then reverted to 1.1 when I read of some problems in 2.0.
I haven't done a free air calibration on the LM-1 as I read it's only necessary when the sensor is replaced. Suggestions?
To get more resolution, I followed Meents setup by using 0-5V=11-17AFR, and using a custom AFR PID (Volts/.833+11). Almost all of the cells are either hanging right around 14.7-15, or are at 16.9 (mostly at WOT). I double checked all the tables and according to the docs they are right on. Now, I did start with my previous SD tune done months ago under different conditions instead of adding 15% across the board.
If the 14.7 is accurate at idle and cruise, I presume it's accurate at 16.9 as well. So if I trust this, then my VE values are peaking at 115-120 at WOT and I just don't trust that I'm running this lean. Being I'm N/A, this really seems way out there. How would an exhaust leak behave on the wideband?
I compared the AFR reported on the LM-1 to that reported in Logworks 1.1, and it looks right on. HPT appears to be reading the same as the LM-1 display, albeit much faster screen updates. I loaded v1.42 of the LM-1 firmware a few weeks ago as well as Logworks 2.0, but then reverted to 1.1 when I read of some problems in 2.0.
I haven't done a free air calibration on the LM-1 as I read it's only necessary when the sensor is replaced. Suggestions?
03-27-2006, 04:09 PM
#2
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You don't have PE disabled do you?
I recallibrate my LM1 every so often.
If I'm ever in question of what it's reading or it seems to fluctuate more than usual then I recal it.
I open the throttle on the car and stick my shop-vac hose on the tailpipe and blow air through the exhaust to clear it with fresh air. I let it blow for several minutes and then recal the LM1.
Keep in mind that you would have serious lean misfires if you were really at 16.9:1 AFR at WOT. It sounds like you might have the scaling backwards.
I recallibrate my LM1 every so often.
If I'm ever in question of what it's reading or it seems to fluctuate more than usual then I recal it.
I open the throttle on the car and stick my shop-vac hose on the tailpipe and blow air through the exhaust to clear it with fresh air. I let it blow for several minutes and then recal the LM1.
Keep in mind that you would have serious lean misfires if you were really at 16.9:1 AFR at WOT. It sounds like you might have the scaling backwards.
03-27-2006, 10:02 PM
#3
I found a very slight crack in my driver side collector with soot on it. Not sure how much that is affecting it. Guess I'll be adding another bung post-catalytic on the passenger side and move it. Seems pretty difficult to patch those leaks, especially those in between the collector pipes.
I'm having problems getting my LM-1 to re-calibrate to free air. Pressing/holding the calibrate button doesn't do anything on it
I don't think I've disabled PE. I've never done it before and the HPT help files doesn't mention it either.
I'm having problems getting my LM-1 to re-calibrate to free air. Pressing/holding the calibrate button doesn't do anything on it
I don't think I've disabled PE. I've never done it before and the HPT help files doesn't mention it either.
Last edited by JimMueller; 03-27-2006 at 10:23 PM.
03-28-2006, 08:10 AM
#4
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You don't need to disable PE that I'm aware of...
You'd be surpized how much a small leak will throw your numbers. I had a band clamp torqued to 50 ft/lbs on my left bank (right near the WB). This threw my AFR's on the left bank off by 20% compared to the right bank. Torqued the band clamp to 70 ft/lbs and the two banks read within 3% of each other. There was no visible carbon leaks from the band clamp either.
You'd be surpized how much a small leak will throw your numbers. I had a band clamp torqued to 50 ft/lbs on my left bank (right near the WB). This threw my AFR's on the left bank off by 20% compared to the right bank. Torqued the band clamp to 70 ft/lbs and the two banks read within 3% of each other. There was no visible carbon leaks from the band clamp either.