For the first time I had trouble passing California's bi-annual smog check. The results are in the table below.
This for a 1994 Buick Park Avenue Ultra GM's 3.8L Series 1 with a supercharger, but would apply to many vehicles.
First attempt failed because of a small leak in the EVAP system but told verbally vehicle passed the emissions portion that they do first. No charge and no paperwork so no readings.
Second attempt EVAP failed and emissions were not even tested
Third attempt EVAP passed after smoke testing and finding a signicant leak under car near rear passenger door. Failed emmissions because of high NOX at 25 mph 532 with 491 allowed. I could not find any issues so I changed air filter, spark plugs, oil, coolant & added Redline Water Wetter, tires to 35 psi. I was doing small things hoping for the 10% improvement that I needed.
Fourth attempt drove 50 miles on freeway to get fully up to temp. NOX increased signifcantly from 532 to 656 at 25 mph with 491 allowed and from 301 to 624 with 481 allowed. Instead of improvimg emissions they got significantly worse, especially the NOX. I assumed EGR valve failure or blocked passage way. I complete dissablemed the EGR system, bench tested, reinstalled smoke testing, and finally road testing. I found no issues and the command and position voltages using an Actron CP9185scanner were the same and responded as expected. One aspect that still concerns me is electrically disconnecting the EGR valve, and applying an 9 volt external voltage to pins A & E hear the valve click open and having tested this operation on the bench I expected the engine to stuble if not stall. There was no change. Had I not arleady bench verifed the EGR valve opening and closing with 9 V and clear passage way I would have been confident that one of these two ites was an issue. Being unable to find any reach for the RAPID increase in NOX is used a can of CRC Intake Valve clearned followed by a bottle of Redline's fuel injector clearner. I noticed no different in the engine's performance or any of the reading using the Acrtron CP9185scanner.
Fifth attempt I drove conservatively for 9 miles to get the coolant close to operating temperature and the engine block still as cool as possilble. Frankly, I was expected to fail and was pleasantly surprised that I passed.
At this point I am try to understand what the issue was and add that to my knowledge of things to check. My working theory is it was not the valve or fuel injector cleaners as these issues occur rapidly. I am leaning towards a combination of the relatively cool engine block and lower tire pressure. Engine block temp because it would have been the hotest for 4th attempt which had the highest NOX emissions and would also be a sudden change. The low tire pressure because in my mile of test driving, I think the EGR command was triggering at a higher speed than the smog test. by lowering the tire pressure, I was able to get the EGR command to trigger at a slightly slow speed.
Here is the table and I'm looking for suggestions on why my NOX increased so dramatically and quickly and what I did to lower the level to pass smog. So would be appreciative of links t o authority websites on the signifance of the smog results and what to do to lower emissions. So many of the sites are contradictory such as higher/lower octane. Most suggest fully warming a vehicle up and increasing tire pressure yet this is when I got my worst results and I passed with a cool engine block and intentially lower tire pressure.
This for a 1994 Buick Park Avenue Ultra GM's 3.8L Series 1 with a supercharger, but would apply to many vehicles.
First attempt failed because of a small leak in the EVAP system but told verbally vehicle passed the emissions portion that they do first. No charge and no paperwork so no readings.
Second attempt EVAP failed and emissions were not even tested
Third attempt EVAP passed after smoke testing and finding a signicant leak under car near rear passenger door. Failed emmissions because of high NOX at 25 mph 532 with 491 allowed. I could not find any issues so I changed air filter, spark plugs, oil, coolant & added Redline Water Wetter, tires to 35 psi. I was doing small things hoping for the 10% improvement that I needed.
Fourth attempt drove 50 miles on freeway to get fully up to temp. NOX increased signifcantly from 532 to 656 at 25 mph with 491 allowed and from 301 to 624 with 481 allowed. Instead of improvimg emissions they got significantly worse, especially the NOX. I assumed EGR valve failure or blocked passage way. I complete dissablemed the EGR system, bench tested, reinstalled smoke testing, and finally road testing. I found no issues and the command and position voltages using an Actron CP9185scanner were the same and responded as expected. One aspect that still concerns me is electrically disconnecting the EGR valve, and applying an 9 volt external voltage to pins A & E hear the valve click open and having tested this operation on the bench I expected the engine to stuble if not stall. There was no change. Had I not arleady bench verifed the EGR valve opening and closing with 9 V and clear passage way I would have been confident that one of these two ites was an issue. Being unable to find any reach for the RAPID increase in NOX is used a can of CRC Intake Valve clearned followed by a bottle of Redline's fuel injector clearner. I noticed no different in the engine's performance or any of the reading using the Acrtron CP9185scanner.
Fifth attempt I drove conservatively for 9 miles to get the coolant close to operating temperature and the engine block still as cool as possilble. Frankly, I was expected to fail and was pleasantly surprised that I passed.
At this point I am try to understand what the issue was and add that to my knowledge of things to check. My working theory is it was not the valve or fuel injector cleaners as these issues occur rapidly. I am leaning towards a combination of the relatively cool engine block and lower tire pressure. Engine block temp because it would have been the hotest for 4th attempt which had the highest NOX emissions and would also be a sudden change. The low tire pressure because in my mile of test driving, I think the EGR command was triggering at a higher speed than the smog test. by lowering the tire pressure, I was able to get the EGR command to trigger at a slightly slow speed.
Here is the table and I'm looking for suggestions on why my NOX increased so dramatically and quickly and what I did to lower the level to pass smog. So would be appreciative of links t o authority websites on the signifance of the smog results and what to do to lower emissions. So many of the sites are contradictory such as higher/lower octane. Most suggest fully warming a vehicle up and increasing tire pressure yet this is when I got my worst results and I passed with a cool engine block and intentially lower tire pressure.
| Date | milage | EVAP | speed|rpm | Emissions | CO2 | O2 | HC | CO | NO |
| 9-Jan | 219849 | failed | verbal pass | n/a | n/a | n/a | n/a | n/a | |
| No issues located replaced a couple marginal hose connections | |||||||||
| 16-Jan | 219885 | failed | not checked | ||||||
| Smoke test located a bad hose connector under body by rear passenger door | |||||||||
| 22-Jan | 219914 | passed | 15 | 1852 | passed | 15.06 | 0.34 | 52/58 | 0.14/0.33 | 301/481 |
| passed | 25 | 1777 | failed | 15.30 | 0.21 | 32/33 | 0.07/0.31 | 532/481 | ||
| No issues found changed air filter, spark plugs, oil, coolant & add Redline Water Wetter, tires to 35 psi, driven 50 miles on freeway to get fully up to temp | |||||||||
| 16-Feb | 220116 | passed | 15|1844 | failed | 15.00 | 0.24 | 42/58 | 0.09/0.33 | 624/481 |
| passed | 25|1741 | failed | 15.00 | 0.22 | 36/33 | 0.06/0.31 | 656/481 | ||
| EGR system disassembled, inspected & smoke tested, valve bench, road, and forced open, CRC Intake valve cleaner, Redline Fuel injector cleaner, tires to 22 psi, conservative 9 mile drive for operating temp but cool block | |||||||||
| 5-Mar | 220364 | passed | 15|1821 | passed | 15.01 | 0.39 | 51/58 | 0.13/0.33 | 335/481 |
| passed | 25|1760 | passed | 15.10 | 0.3 | 33/33 | 0.08/0.31 | 381/481 |
