Some rather general things I've noticed about smog checking here in San Jose, Calif. They use the dyno test here now. Idle, 15 mph & 25 mph. They also do the full visual inspection, & even pressurize the evap system to see if it works. Many states are using something similar to this.
I'm guessing that people here will get/do a basic tune up FIRST; Air filter, plugs, fuel filter, PCV valve checked/replaced, etc. Having the "Check engine" light on, or having it come on during the test will flunk your car here.
So, some ideas for fixing failed Nox smog checks, including some premptive ones. Hopefully it will also save some people money in restests as well:
1. Being too lean raises Nox, to a point. If one injector is too rich/lean, then the other injectors try to "make up for it". However, this would cause rough idle/running, and uneven plug colors. Lean problems can also be from a fuel regulator adjusted too low. I also don't like "performance" chips that tinker with the air/fuel ratio, except for something like cold start stall fixes. If the mixture is way lean, you will have misfire/power fall off problems.
2. EGR not working/plugged. Again, if your hi-perf chip turns off the EGR, you'll be in big trouble trying to pass the dyno Nox test (To say nothing of detonation at part throttle with no EGR, unless the chip cuts back base timing. EGR is cut off at WOT anyhow). Also, vacuum tubing for the EGR can get cracks, splits, etc., and the diapragm can develope leaks, dropping the EGR flow too low. Thermal senors can fail in vacuum lines. Another VERY common problem is carbon in the EGR passages. If you've never taken off the EGR valve, go get a gasket for it, & take it off, & cleanout those passages, including the manifold ones, before a smog check. They were testing EGR function around here for years before the dyno Nox tests came along.
Be aware that aftermarket EGR valves may not perform the same as the OEM ones. Passage sizes & diaphragm sizes affect EGR flow. Thank to Joe for reminding me about this. When I replaced the EGR valve on my '84 Crown Victoria wagon 5 liter there were 8 different EGR valves in the catalog, all for the same displacement engine!
The maker of the car doesn't matter about the carbon in the EGR passages problem if it has EGR. I've had the carboned up EGR passages problems on an (true) Olds 350, Buick 455, and a Ford 302. So, when I get Dad's 1987 GN, off comes the EGR so I don't have to reinvent the wheel (pay for a retest).
Some cars use an EGR valve position sensor (a potentiometer type of sensor), which DO also go bad, causing ECM codes, & confuse the ECM. Easy to check when the EGR valve is off with a VOM. This last part may not apply to your Turbo Buick, but maybe another car of yours may need this sensor looked at.
3. Higher compression. While putting high compression pistons in a Turbo is not a good idea, I never know if someone would do it. But, carbon build up is a real common problem. Yes, you could pull the heads, but I find a good chemical cleaning much easier. Gumout's Regane & Chevron's Cleanup work good, although I love a local brand, Clean Power, and it worked great for getting a car of mine to pass Nox. The injectors also get cleaned good with these chemicals. I also tend to favor chemicals over driving at 100mph for a hour to remove carbon. But, to each their own.
I don't know if 100 octane street legal unleaded would help the carbon build up or not. And since no one in their right mind should be using low octane gas in a Turbo Buick, I don't want to get into that.
If you do take the heads off, this is another vote for polishing the combustion chambers.
4. Clear the ECM, then drive a few miles at the speeds that will be used on the dyno run is a good idea. Make this the last step after all of these steps, so you force the ECM to relearn. I'm glad the ECM is easy to clear on the Buick Turbo. On my '94 Olds Achieva, I have to remove the battery cable, wait 20+ minutes, then reset the #%@$ clock & radio.
5. Catalytic converter not working? If it has an O2 sensor, it uses a 3 way catalyst. Yes, they do die, but I need some feed back on how often the Nox Reducer section fails. But, if you've installed a straight pipe, or hollowed out your converter, you better fix that FIRST. A rap of a wrench on a converter housing is a dead give away that it's been hollowed out, FYI.
6. O2 sensor? Yes, it could be bad and cause high Nox, but what I hear it normally makes the engine run too rich. And if you've been running leaded race gas, or using MMT based octane boosters, both the O2 sensor & catalytic converter are probably dead. The O2 sensor doesn't like coolant in the air/fuel mixture, or high oil consumption, either. You can check the O2 function with a good auto diagnostic scope.
7. Ignition timing? Yes, retarding the timing a little can help both Nox & HC emissions. But, with the later Turbo Buicks (and a number of other cars), it's almost impossible to change the initial timing. And if you "trick" up the advance curves in either the chip, or in a distributor type of ignition, you can cause Nox failures.
Thanks to Joe Cheung for a critique of my first draft of this.
Feel free to take me to task on this, I'm still learning.
-Mike H.
I'm guessing that people here will get/do a basic tune up FIRST; Air filter, plugs, fuel filter, PCV valve checked/replaced, etc. Having the "Check engine" light on, or having it come on during the test will flunk your car here.
So, some ideas for fixing failed Nox smog checks, including some premptive ones. Hopefully it will also save some people money in restests as well:
1. Being too lean raises Nox, to a point. If one injector is too rich/lean, then the other injectors try to "make up for it". However, this would cause rough idle/running, and uneven plug colors. Lean problems can also be from a fuel regulator adjusted too low. I also don't like "performance" chips that tinker with the air/fuel ratio, except for something like cold start stall fixes. If the mixture is way lean, you will have misfire/power fall off problems.
2. EGR not working/plugged. Again, if your hi-perf chip turns off the EGR, you'll be in big trouble trying to pass the dyno Nox test (To say nothing of detonation at part throttle with no EGR, unless the chip cuts back base timing. EGR is cut off at WOT anyhow). Also, vacuum tubing for the EGR can get cracks, splits, etc., and the diapragm can develope leaks, dropping the EGR flow too low. Thermal senors can fail in vacuum lines. Another VERY common problem is carbon in the EGR passages. If you've never taken off the EGR valve, go get a gasket for it, & take it off, & cleanout those passages, including the manifold ones, before a smog check. They were testing EGR function around here for years before the dyno Nox tests came along.
Be aware that aftermarket EGR valves may not perform the same as the OEM ones. Passage sizes & diaphragm sizes affect EGR flow. Thank to Joe for reminding me about this. When I replaced the EGR valve on my '84 Crown Victoria wagon 5 liter there were 8 different EGR valves in the catalog, all for the same displacement engine!
The maker of the car doesn't matter about the carbon in the EGR passages problem if it has EGR. I've had the carboned up EGR passages problems on an (true) Olds 350, Buick 455, and a Ford 302. So, when I get Dad's 1987 GN, off comes the EGR so I don't have to reinvent the wheel (pay for a retest).
Some cars use an EGR valve position sensor (a potentiometer type of sensor), which DO also go bad, causing ECM codes, & confuse the ECM. Easy to check when the EGR valve is off with a VOM. This last part may not apply to your Turbo Buick, but maybe another car of yours may need this sensor looked at.
3. Higher compression. While putting high compression pistons in a Turbo is not a good idea, I never know if someone would do it. But, carbon build up is a real common problem. Yes, you could pull the heads, but I find a good chemical cleaning much easier. Gumout's Regane & Chevron's Cleanup work good, although I love a local brand, Clean Power, and it worked great for getting a car of mine to pass Nox. The injectors also get cleaned good with these chemicals. I also tend to favor chemicals over driving at 100mph for a hour to remove carbon. But, to each their own.
I don't know if 100 octane street legal unleaded would help the carbon build up or not. And since no one in their right mind should be using low octane gas in a Turbo Buick, I don't want to get into that.
If you do take the heads off, this is another vote for polishing the combustion chambers.
4. Clear the ECM, then drive a few miles at the speeds that will be used on the dyno run is a good idea. Make this the last step after all of these steps, so you force the ECM to relearn. I'm glad the ECM is easy to clear on the Buick Turbo. On my '94 Olds Achieva, I have to remove the battery cable, wait 20+ minutes, then reset the #%@$ clock & radio.
5. Catalytic converter not working? If it has an O2 sensor, it uses a 3 way catalyst. Yes, they do die, but I need some feed back on how often the Nox Reducer section fails. But, if you've installed a straight pipe, or hollowed out your converter, you better fix that FIRST. A rap of a wrench on a converter housing is a dead give away that it's been hollowed out, FYI.
6. O2 sensor? Yes, it could be bad and cause high Nox, but what I hear it normally makes the engine run too rich. And if you've been running leaded race gas, or using MMT based octane boosters, both the O2 sensor & catalytic converter are probably dead. The O2 sensor doesn't like coolant in the air/fuel mixture, or high oil consumption, either. You can check the O2 function with a good auto diagnostic scope.
7. Ignition timing? Yes, retarding the timing a little can help both Nox & HC emissions. But, with the later Turbo Buicks (and a number of other cars), it's almost impossible to change the initial timing. And if you "trick" up the advance curves in either the chip, or in a distributor type of ignition, you can cause Nox failures.
Thanks to Joe Cheung for a critique of my first draft of this.
Feel free to take me to task on this, I'm still learning.
-Mike H.
