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Courtesy of Mike Wassall
Passing Smog (Hopefully)
|Retarded timing||Decrease||Same or increase||No change||No change||Large decrease|
|Very retarded timing||Some increase||No change||Some to large decrease||No change||Large decrease|
|Advanced timing||Increase||Same or less||No change||No change||Large increase|
|Rich mixture||Some to large increase||Large increase||Some increase||Decrease||Decrease|
|Lean mixture||Increase||Large decrease||Decrease||Increase||Some to large increase|
|Very lean mixture||Large increase||Large decrease||Decrease||Large increase||Some to large decrease|
|Ignition Miss||Large increase||Some decrease||Some decrease||Some to large increase||Some to large decrease|
|Compression loss||Some to large increase||Decrease||Decrease||Increase||Some to large decrease|
|Worn engine||Increase||Increase||Decrease||Decrease||Same or less|
|Air injection||Large decrease||Large decrease||Some to large decrease||Large increase||No change|
|EGR working||No change||No change||Some decrease||No change||Large decrease|
|EGR leaking||Increase||No change||Same or less||No change||Same or less|
|Cat working||Decrease||Decrease||Increase||Increase||Decrease with 3-way cat|
With the coming of Smog II, aka treadmill smog testing to my area soon, Ive been doing some reading up on smog testing/controls etc. As luck would have it, a friend who is in the trade and studying up for his end of Smog II, meaning his testing license, was kind enough to lend me some of his books. So the table above is a compilation from the prep books for the state test. I am not a smog tech, or automotive professional, it is just a hobby. While the above chart should hopefully prove useful, I do have a few more comments to pass on from my readings and personal experience.
If your car has an O2 sensor it has to be working to have a chance of passing. Test it with a decent quality analog meter or any digital multimeter. With the engine running and warmed up, the O2 sensor should be putting out about a half a volt, DC. Actually the books say averaging .45 volts. And it should be bouncing back and forth, always swinging up and down, from .15 up to .7, at least, more likely from less than .1 up to over .8. But it should be up and down. And the testing should be done with it hooked up to the harness, not disconnected. If it is zero, it is likely dead, they do die and replacement is recommended every 30k, test it disconnected from the harness to verify, and replace it if necessary. I have had them last much longer than that and not much over 20k, so you never know. A high reading indicates rich, low a lean condition. If it runs low, it will probably pass as long as it isnt misfiring, as long as you dont have to pass Nox. If it is rich, it probably wont pass. At idle, adjusting the bypass screw in the AFM can compensate for some excessive richness, but really isnt the cure but may work as long as you can get it to cycle up and down. A tight exhaust system at least to the cat is necessary, it turns out an exhaust leak is something of an in and out thing and will suck in some air and give a false reading to the O2 sensor which will in turn richen things up since it sees too much oxygen.
If your car is pre oxygen sensor, adjusting the AFM bypass screw will make a definite change in your idle readings, back it out to lean it out, but will make little if any difference in high rpm emissions.
High CO indicates a rich condition according to the state books. But it can also be caused by gas in the oil if it has been running too rich, so change the oil if CO is high or you suspect it might be. It tends to be more of a problem with carbureted cars, but sticky or dirty injectors could also do it on injected cars.
My friend the smog tech says often, not always, but often using the Guaranteed to Pass stuff from the auto parts store will in fact make it pass. I have never used it, but he says it frequently works. Fuel injector cleaner can also help, I have had some success with Techron, and I have heard very good reports about something called I think it is BK44. I havent used it, I dont even know who makes it, but those are the only two that seem to get recommended.
If you are fighting a high Nox problem, or even if you have to pass it, the state test books say running premium gas can help. Id always thought premium was just for octane, but apparently it can do a little more in some circumstances.
A warmed up cat can make a huge difference, I recently smogged my 87 E24 project car that has all of 180 miles on it in the past two and a half years. At first on the machine it was reading about 600 PPM on HC, which is way too high. After a good high RPM burn in (70F degree day and the car was already warmed up to normal temp with an 80C thermostat) the idle reading dropped to 44PPM, and the 2500 reading was 6PPM. Now I have a problem, I know that, I need to put some miles on it and figure out what is going on, but that shows what a good working cat can do. But it shouldnt be necessary, a 528i with a bad cat, but running good is likely to be about 200PPM. Borderline for passing, but nothing like my 6er was.
Passing smog, the number one thing is make sure the timing isnt too far advanced, that will make it very hard to pass. Even try retarding the timing a bit as long as they dont check it like they are supposed to in California. But it shouldnt really be necessary on 528is and the 530i already had very retarded timing. And make sure the vacuum retard is working also or else that will create related problems. Make sure it is running right and in good tune, plugs OK or better, fresh points if it has them, reasonably clean oil and air filter. One thing that might make a little bit of difference if youre are right on the borderline is adjust the valves a little loose, that is the same as a milder cam and could make the difference if you are close, loose like .014, or .016, or even .018, but it will make noise at that point but shouldnt hurt anything besides your ears.
Like I said, Im no expert on this subject, but I do know (or have read) a little bit. I hope this will help you pass what is always a very anxious time for me, smogging a car.
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