Smog results, High NOx and solution
02-16-2008, 08:10 PM
#1
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Smog results, High NOx and solution
Just thought I would post this for our general collection of smog info. Met a new guy local to me, has an 89 S-4 that failed smog. He doesn't do any of his own work, and was very worried about how to fix his situation, and how much $$$$ it would cost him at a shop. Here are the results from his first test:
Spd.........RPM............HC ppm................CO %..............NO ppm........Result
15mph...1391rpm.....21(110max)...... .02(.71max)......426(772max) PASS
25mph...1216rpm.....16(85max)........ .00(.59max)......1028(711max) FAIL
So when Eric first called me and said he failed, I recommended he check for vacuum leaks, get the car very warm before the test and try again. His first test was without warming the engine, just drove straight to the smog station a couple blocks from his house. Here are the second test results (I omitted the HC and CO, they were still fine):
Spd.........RPM............NO ppm..........Result
15mph...1419rpm......1479(772max) FAIL
25mph...1223rpm......1404(711max) FAIL
Wow, almost off the scale now. I offered to help him get it to pass, so he brought the car over. My first thought was to swap the MAF, and see what the new readings would be. We reset the computer along with the MAF swap and headed to a different smog shop. Here are the third test results:
Spd.........RPM............NO ppm..........Result
15mph...1366rpm......744(772max) PASS
25mph...1235rpm......761(711max) FAIL
Now we are close, the slow speed test just passed, and the higer speed test failed by only 50ppm. My thought was we didn't drive long enough to set the computer, and the engine was warm but not warm enough. So we toppped off with some new gas, and went for a nice drive down the interstate, and along the river levee. About 30 miles in all, mainly because it was a beautiful day and a fun drive. Definitely worked the engine. Then straight back to the smog shop. Smog guys got it right in, ran the test again, and here are the results:
Spd.........RPM............NO ppm..........Result
15mph...2140rpm......386(772max) PASS
25mph...1427rpm......710(711max) PASS
It passed...just barely!!!! The 25mph test passed by 1ppm! Smog guys asked what we did, and laughed when we said we gave it an Italian Tune Up. Interesting to note the first 3 tests were run at similar RPM's, but the final test has much higher low speed RPM, and only slightly higher RPM's for the higher speed test. The low speed results were waaaay down compared to the previous test.
Anyway, to sum it up, all we did was swap the MAF. If needed, we were set to swap out the cats and O2 sensor, but thankfully we avoided that.
Hope this can help someone in the future with similar readings.
Rich
Spd.........RPM............HC ppm................CO %..............NO ppm........Result
15mph...1391rpm.....21(110max)...... .02(.71max)......426(772max) PASS
25mph...1216rpm.....16(85max)........ .00(.59max)......1028(711max) FAIL
So when Eric first called me and said he failed, I recommended he check for vacuum leaks, get the car very warm before the test and try again. His first test was without warming the engine, just drove straight to the smog station a couple blocks from his house. Here are the second test results (I omitted the HC and CO, they were still fine):
Spd.........RPM............NO ppm..........Result
15mph...1419rpm......1479(772max) FAIL
25mph...1223rpm......1404(711max) FAIL
Wow, almost off the scale now. I offered to help him get it to pass, so he brought the car over. My first thought was to swap the MAF, and see what the new readings would be. We reset the computer along with the MAF swap and headed to a different smog shop. Here are the third test results:
Spd.........RPM............NO ppm..........Result
15mph...1366rpm......744(772max) PASS
25mph...1235rpm......761(711max) FAIL
Now we are close, the slow speed test just passed, and the higer speed test failed by only 50ppm. My thought was we didn't drive long enough to set the computer, and the engine was warm but not warm enough. So we toppped off with some new gas, and went for a nice drive down the interstate, and along the river levee. About 30 miles in all, mainly because it was a beautiful day and a fun drive. Definitely worked the engine. Then straight back to the smog shop. Smog guys got it right in, ran the test again, and here are the results:
Spd.........RPM............NO ppm..........Result
15mph...2140rpm......386(772max) PASS
25mph...1427rpm......710(711max) PASS
It passed...just barely!!!! The 25mph test passed by 1ppm! Smog guys asked what we did, and laughed when we said we gave it an Italian Tune Up. Interesting to note the first 3 tests were run at similar RPM's, but the final test has much higher low speed RPM, and only slightly higher RPM's for the higher speed test. The low speed results were waaaay down compared to the previous test.
Anyway, to sum it up, all we did was swap the MAF. If needed, we were set to swap out the cats and O2 sensor, but thankfully we avoided that.
Hope this can help someone in the future with similar readings.
Rich
02-16-2008, 09:41 PM
#2
Race Director
This was an interesting day..........my 1st thoughts were air leak or failed cats causing a lean condition.... I didn't think the MAF would help...since a bad MAF would default to super rich....since the 89 ran fine....and ran the same after the MAF swap.....so maybe it is slowing dying & out of spec, but not failed yet.... I would guess the cats are marginal....but barely hanging on.... Either way it really doesn't matter...since its good for 2 years.... :>)
Whats odd is the HC was very low....again pointing towards a lean condtion....so I reviewed my last smog almost 2 years ago...car was cold, so the HC was barely passing, but the NO was super low at 56....
Whats odd is the HC was very low....again pointing towards a lean condtion....so I reviewed my last smog almost 2 years ago...car was cold, so the HC was barely passing, but the NO was super low at 56....
