View Full Version : The time of year all CA residents HATE...SMOG CHECK

01-04-2011, 08:42 PM
sooo, its time for my bi-yearly smog check. last year the car BARELY passed. i didn't do any of the usual tricks though. just drove it straight to the smog check center shut it off and waited my turn. I know of the ISO-HEET and drive it hard on the freeway before you get it tested trick but any other suggestions guys???

01-04-2011, 09:33 PM
Move out of CA?

but seriously aside from doing a good tune up and making sure you have clean filters, good plugs, proper timing, and good fuel (Chevron or 76 is my preference), I dont really have any suggestions. The last time I smogged a car it was when most cars still had carburators and mechanical timing. All my tricks revolved around that.

01-04-2011, 09:52 PM
yeah just did a oil change and changed my plugs 3 weeks ago. might change the oil again but it still looks really clean. but im gonna throw a new air filter in today. About the timing im not sure about how adjusting it works. A co-worker told me i should retard the timing if i have any issues passing by SLIGHTLY turning the distributor away from the engine. but im going to look into that in my Chilton manual. i have a 91 ST btw.

01-05-2011, 01:08 AM
I wouldnt recommend tweaking the timing out of spec, but I would recommend making sure its correct to factory specs. You would need a timing light (which you can rent for free from Autozone if need be) and then follow the proceedure in the BGB.

If you dont pass on the first try I do have one trick that you can try, but I would wait and see if you pass without it first.

01-05-2011, 02:03 AM
Taking it for a run on the highway isn't a trick, it's ensuring you're not screwing yourself. The catalytic converter has to be at proper operating temperature to work at full efficiency. Taking the test with a cold cat is choosing to take it with a partially functioning emissions control system.

A tuneup's a good idea -- make sure your distributor and rotor, if not in need of replacement, are at least clean. Same goes the the throttle body. You don't mention what model or year you're driving, but the PCV valve/hose are good to check and cheap to replace if needed.

Failure to pass emissions testing usually indicates something is wrong in your engine; even if it's working, that's probably courtesy of the ECU trying to compensate. A lot of the work people complain about having to do to get past emissions testing falls under another category: basic maintenance.

01-05-2011, 02:23 AM
i drive a 91 ST with a rebuilt engine swap with around 50-60,000 miles on it so i HOPE theres no engine issues. Im gonna take the car for a pretest first and see how that goes but i'll definitely check out the distributor and clean the cap if needed.

joe's gt
01-05-2011, 06:01 AM
Just drive it around a little bit to heat the cat up, everything will work itself out as long as ur emissions system is functioning properly.

01-05-2011, 05:17 PM
ok. Taking it out for a drive in about 15 minutes. Will post results after. Not sure if I want to add the Iso Heet though.

01-05-2011, 07:19 PM
Watching monitors as he runs test now....

01-05-2011, 07:37 PM
Ok. So I failed. Passed everything EXCEPT NO. Max was 577 at 15mph and I got 721. Max at 25mph was 535 and I got 709. Also HC was very high. Max 101, measured 99. Any help or suggestions?

01-05-2011, 08:03 PM
I wouldn't recommend changing your oil right before a test. New oil has detergents and other chemicals that burn off within the first few miles. This can affect the tests.

01-05-2011, 08:10 PM
How old is your O2 sensor? That little guy can be all the difference on the HCs. Before I went last, I swapped out a bunch of vacuum hose and sealed up my PCV valve. Another good place to look is your EVAP can. That guy seems to get the most neglect out of cars I have bought in the past.

01-05-2011, 08:25 PM
Check out the EGR system, make sure its plumbed correctly and I would take the time to pull off the valve and hoses and make sure you have a clean passage all the way though into the intake. You also want to make sure the valve is closeing all the way and seating. Many times the seat gets covered in carbon and keeps the EGR open a little bit creating a lean condition which leads to high NOx.

The next suspect is the O2 sensor. I believe they are spec'd to be replaced every 50K so if its been even close to that long I would replace it.

When was the last time you changed your fuel filter?
Have you ever run any fuel injector cleaner through the system (or do you run Chevron gas most of the time)
Any chance your fuel pump might be worn out?

The high HC and NOx at the same times tells me you may also have other issues though. It says you have both a lean condition at cruise and are still not burning all your fuel.
It could just be your Cat but I would like to see a compression test done as well. You need to verify timing is dead on factory specs, and I would triple check your plugs, wires, cap and rotor.

01-05-2011, 08:29 PM
Changed the O2 sensor about 3 months ago. Bosch one. And I changed the oil 3 or so weeks ago. Don't know what or where pvc valve is but I'm gonna take a look in my chilton manual now. The smog place gave me some paper work about a government assistance program bt I was told it takes 9 weeks to process and I start school the 22nd of this month and my tags expire this month.

01-05-2011, 10:25 PM
From Car Sound (MagnaFlow's parent company), which makes catalytic converters, high NO and CO: Replace converter, tune-up & check lean AFR, leaking exhaust valves (this ties in with Facime's carbon-encrusted valve suggestion).

NOx is indicative of high combustion temperatures; this is the point of the EGR, which lowers the temperature by introducing burnt gases. High HC is often indicative of a converter not properly warmed up, or questionable ignition. If you've got bad ignition on one cylinder where fuel is getting by unburnt, this might explain why the rest of the mix is coming up as lean -- the ECU is trying to compensate for the entire engine based on one or two bad cylinders because it thinks it has a rich AFR and therefore starving the other cylinders, but that's just speculation on my part.

01-06-2011, 12:32 AM
Hoping its not a bad cylinder. That's the reason I had to have the engine replaced in the first place when I 1st got the car.

01-06-2011, 03:03 AM
a simple compression test can either point to a more significant problem and/or rule out a whole bunch of speculation. Its one of the simplest tests to perform, takes no more than 30 minutes to do even for a noob and requires only a compression test gauge (which you can rent from Autozone) and a spark plug wrench (socket, extension and ratchet). Its ALWAYS the very first test on my list whenever I start into a diagnostic.

01-06-2011, 03:44 AM
Ok just read into my manual on how to do a compression test. Sounds simple enough. I'm going to check out kragen in to morning to see about a compression test gauge and try that before I take it to a shop for a diagnostic if I HAVE to go that route.

joe's gt
01-06-2011, 03:54 AM
Make sure your timing is 10* BTDC

01-06-2011, 04:07 AM
^^ Agreed

I dont know if Kragen "rents" tools like Autozone does (Autozone doesnt rent either, they loan tools with a fully refundable deposit), but if they dont I'll say this. The first three tools I bought outside of hand tools were a timing light, a compression tester and a multimeter. They arent used that often but they have MORE than paid for themselves over the 20+ years Ive owned them. Just this year my timing light finally dies...time for a new one.

01-06-2011, 05:11 AM
So i should retard the timing?

01-06-2011, 05:36 AM
I dont think Retarding it would help you at all. i think i would hurt you more than anyhting.

01-06-2011, 06:00 AM
What about iso heet. How much do you think that'd reduce my NO and HC emissions.

01-06-2011, 06:14 AM
Advancing (if anything) the timing would help slightly. I know nothing about ISO-heet, but find pour in remedies for ANYthing to be less than effective most times.

The trick I mentioned earlier that could have helped was to mess with the AFM spring to trick the ECU to lean out or richen the mixture, the problem is you cant do either or you tip the balance between NOx and HC and fail either way. If you had only failed one or the other my trick would have helped.

01-06-2011, 03:41 PM
NOx is indicative of high combustion temperatures; this is the point of the EGR, which lowers the temperature by introducing burnt gases. [/SIZE][/FONT][/SIZE][/FONT]

I found this interesting just in passing. It seems counterintuitive that re-introducing combustion gasses into the intake would lower temperatures.. it seems like it would do the opposite. I know this is kind of tangent to the current topic, but it sounded odd to me.

High NOX indicates a lean condition, but does that necessarily mean high temperatures? Isn't the point of the EGR to basically put some exhaust back through the combustion cycle to try to burn more out of it?

01-06-2011, 10:21 PM
no, the exhaust gases are inert gas. (edit: its inert because all the oxygen has been burned out of it already) Adding it adds neither oxygen nor fuel so in essense dilutes the mixture which makes for a cooler explosion. Lean mixture = higher temp to begin with thus the old adage of lean = power. The balance is struck somewhere between lean for economy and power and the high temps being hard on the motor, increasing the risk of detonation and/or melting something.

Lean = economy not so much just because you are using less fuel per stroke but because at the lean edge you make more power therefore you use less pedal.

01-06-2011, 11:43 PM
Well if that's the case, I am having an even harder time figuring out how an EGR system is supposed to reduce emissions in any meaningful way. What you are describing sounds like an attempt at some sort of engine preservation/safety measure, which clearly is unnecessary as an emissions control device. How does a diluted, cooler explosion reduce the actual PPM of a gas in the exhaust mixture (thinking in terms of conservation of matter here)? Being lean causes the high temps, so if you want lower temps, you add fuel.. why introduce an extra variable and use the spent combustion gasses to artificially effect the exhaust temps instead of properly tuning the air/fuel mix? Cars all over the world operate without EGRs to no ill effect, is it a relic of carbed vehicles that for some reason we keep? I've never really heard a satisfactory explanation for the purpose. It seems nonsense to me that recirculating the exhaust gas is going to change the composition of the exhaust, especially when it's stated that there is no actual reaction in the combustion process with the inert re-introduced gasses. What am I still missing?

01-07-2011, 12:15 AM
The wiki explains it better than I ever could.


edit: I guess what i failed to finish saying in my last reply is that since lean equal power and economy but also equal heat, the increased heat also produces more NOx. The point of the EGR system is to reduce the temp while maintaining a lean mixture (thats why you dont just add more fuel, because doing so increases HC). Is it elegant? not really, but it was a simple and effective method at the time these cars were produced.

01-07-2011, 04:36 AM
Ah, ok, that makes more sense. It does seem to me like old tech being held over by the likes of the EPA

01-07-2011, 06:23 AM
a buddy, that is a smog tech, recommended a multi-spark ignition system and runner 1 grade higher fuel.

just a multi-spark ignition would increase NOx, but the higher grade fuel (ie. 89 instead of 87) would bring the level of NOx back down.

i do not know the reasoning or methodology behind his words, so i take it with a large grain of salt until proven...

01-07-2011, 06:50 AM
NOx is formed with lean mixtures because the temperature of the combustion is higher, and it requires more energy (read higher temperatures) for NOx to form. Simply adding fuel to the mix to lower the temperatures does reduce the amount of NOx formed, but then runs into the issue of spewing unburnt hydrocarbons out the tailpipe. This is why Facime indicated messing with the AFR wouldn't work, as fixing one of his issues would worsen the other.