went to do my smog test yesterday, and my car failed. Now I want advice on how to make it pass. I have 95 honda civic si, stock vtec engine, stock intake box, changed oil: Mobil 1 5w 30 yesterday, and used 91 chevron octane. The results:

NO(PPM): measurement 2578 @ 1820 RPM during the 15mph run...supposed to be under 716, which is the maxium number allowed. And 2535 @ 2024 RPM during the 20mph run.

Let me know how you guys would solve this problem. The other measurements passed, only this one FAILED. ...also my timing was off and the guy told me that my cylinder temp was too high.

 

The answer was in your first paragraph. You are using 91 octane. When you put a higher octane into you motor than it actually requires, you are using a lot more fuel than you actually need. See, the higher the octane doesn't mean the higher the quality of the fuel. It is simply a measure of resistance against knock (detonation/pre-ignition). The higher the octane, the more pressure and heat you need to burn it, but the more resistant it will be to knock with that level of compression. So, when you introduce a high octane fuel into a low pressure environment, it doesn't burn completely. The O2 sensors read the results and try to add more fuel. So not only does the mixture not burn properly, but the ecu is trying to fight that and fix it, but it can't. Hence, the test results come out with extra hydrocarbons at the tail pipe.

The answer, use 89. You'll make more power, burn cleaner, pass your smog, get better mileage, and save a little coin. Throw in a tasty tune-up for good measure to ensure that everything is happy. And remember to reset your ecu. It has been trying to learn high octane fuel, and it'll be happier starting from scratch.

 

If your timing is off then theres your answer .. fix the timing check the plugs and go from there

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by delScho &raquo;</TD></TR><TR><TD CLASS="quote">The answer was in your first paragraph. You are using 91 octane. When you put a higher octane into you motor than it actually requires, you are using a lot more fuel than you actually need. See, the higher the octane doesn't mean the higher the quality of the fuel. It is simply a measure of resistance against knock (detonation/pre-ignition). The higher the octane, the more pressure and heat you need to burn it, but the more resistant it will be to knock with that level of compression. So, when you introduce a high octane fuel into a low pressure environment, it doesn't burn completely. The O2 sensors read the results and try to add more fuel. So not only does the mixture not burn properly, but the ecu is trying to fight that and fix it, but it can't. Hence, the test results come out with extra hydrocarbons at the tail pipe.

The answer, use 89. You'll make more power, burn cleaner, pass your smog, get better mileage, and save a little coin. Throw in a tasty tune-up for good measure to ensure that everything is happy. And remember to reset your ecu. It has been trying to learn high octane fuel, and it'll be happier starting from scratch.</TD></TR></TABLE>

Dont listen to this guy he doesnt know what hes talking about.

Looks like you failed on NO? NOs are oxides of nitrogen. NOs are caused by high combustion temps.

EGR valves are used to lower combustion temps to reduce NO emissions. If your motor has an EGR valve then it might be bad. I dont think Honda has used EGR valves in recent years though.

Catalytic converters reduce NO emissions also so it could be a bad catalyst.

Also, I think the guy above has a point about the timing. If your timing is off that could also throw off the NO.


Modified by Mighty at 2:59 AM 7/4/2004

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mighty &raquo;</TD></TR><TR><TD CLASS="quote">

Dont listen to this guy he doesnt know what hes talking about.

</TD></TR></TABLE>

hey jackass, wake up and learn something. What he has stated is absolutely true.
the higher the octane the slower the fuel burns which means, in a low compression engine a lot of the gas is actually wasted because it does not burn completely.

also after you get done freshening up the engine set your timing back to stock

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by dirtyd463 &raquo;</TD></TR><TR><TD CLASS="quote">

hey jackass, wake up and learn something. What he has stated is absolutely true.
the higher the octane the slower the fuel burns which means, in a low compression engine a lot of the gas is actually wasted because it does not burn completely.
</TD></TR></TABLE>

It is not true and if you think it is youre the jackass.

Im not going to a lot of trouble to prove Im right but do you think if higher octane caused worse emissions that California would allow gas stations to sell high octane?

Also, read the guys post. He failed on NO not hydrocarbons. High NO is not caused by incomplete combustion its caused by combustion that is too hot. Jackass.

He is wasting his money by buying high octane but that is all. Its not making his emissions worse or his power better.

And Ive forgotten more **** than you know, sonny.

 

well, if you guys want to get into it, octane is more largely described as the vaporization of a liquid. how they used to test octane was to drop a drop of flammable liquid down the center of a tube. The highest octane gases would actually evaporate totally before the drop hit the ground. This in turn explains why higher compression and forced induction engines need higher octane, more so than the reason that it burns slower. the real reason is that because of the higher octane, the fuel, once compressed before ignition, won't puddle, or form droplets, causing hotspots and detonation. ideally the engine wants the fuel to be in gaseous form in the combustion chamber, but with 12:1 compression it just isn't possible with 87 or 89 octane. normal engines are perfectly fine with regular gas, unless there is carbon build-up, which would necessitate higher octane to avoid detonation.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mighty &raquo;</TD></TR><TR><TD CLASS="quote">Also, read the guys post. He failed on NO not hydrocarbons. High NO is not caused by incomplete combustion its caused by combustion that is too hot. Jackass.</TD></TR></TABLE>



-PHiZ

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mighty &raquo;</TD></TR><TR><TD CLASS="quote">
Dont listen to this guy he doesnt know what hes talking about.
</TD></TR></TABLE>

Actually I do.

But you are right, I didn't have the right answer. It was late, and I totally skimmed past NO in his post. This does sound like a case of a bad EGR. EGRs reduce cylinder temps by reintroducing exhaust gasses during combustion which effectively reduces the amount of clean air that can be burned. Lower cylinder temps are required to keep NO and NO2 from forming during combustion (formation occurs around 2,500° and higher). The catalytic converter also helps NO numbers, and if it's really old, it might need replacement as well. Another way to help reduce NO emissions is to turn back the initial advance a few degrees. Not too many, just like 1 or 2 degrees. This will help.

However, higher octane fuel will hurt his performance and efficiency. That's a fact. It isn't just a waste of money; it's so much more. And sending unburnt fuel into his TWC is not good for it either. Because as it collects exhasut gasses, it gets really hot. Hot enough to burn the fuel. This will kill a catalyst over time. The more fuel dumped, the shorter time it will live.

And I can't speak to octane being a measure of evaporation time. I've never heard of that. But that may be a byproduct of having higher octane, I don't know. But octane is a measure against knock. Plain and simple.

 

Funny stuff.... as others have stated, switching to 89 won't solve your problem. 89 octane burns faster than 91 and would only make your problems worse. The whole point of using 91 octane is is to prevent pre-ingition which greatly increases combustion temps. Very bad for NOx.

Best bet is to keep running 91 octane, figure out your timing issues.

Some other causes:

1) Carbon build up on pistons. If excessive can actually raise compresssion. Also as fuel is introduced into the chamber the carbon acts as a sponge soaking up fuel that then must be burnt. This makes for imcomplete combustion and also leans out the mixture. Again causing more heat. A good rememdy is to use a top engine cleaner. I've found that the GM aresol can works the best. Ford stuff is ok too.

2) Bad Cat Converter. Its possible to have a clean running car in regards to HC/CO levels but fail NOx miserably. Modern three way cats have two functions: Oxidation of HC/Co and reduction of NOx. So it is possible to have a bad NOx reduce side of the cat. As far as i know there is no way to test the NOx part of the cat so replace it as a last step.

3) EGR not functioning. As previously stated though your vehicle is not equipped with it and instead uses valve overlap (vtec) for exhaust gas recirculation.

4) Bad O2 sensor. It's possible for an o2 sensor to work just enough not to cause a CEL but be biased either rich or lean. Slow cross counts can also slow fuel trim correction and mess with the mixture accordingly. Again possible to run lean and combustion temps skyrocket.

Bunch of other possiblities (injector spray patterns for instance) but these are the main culprits. Hope i didn't come across as a know-it-all and i wish you luck.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by delScho &raquo;</TD></TR><TR><TD CLASS="quote">

Actually I do.

But you are right, I didn't have the right answer. It was late, and I totally skimmed past NO in his post. This does sound like a case of a bad EGR. EGRs reduce cylinder temps by reintroducing exhaust gasses during combustion which effectively reduces the amount of clean air that can be burned. Lower cylinder temps are required to keep NO and NO2 from forming during combustion (formation occurs around 2,500° and higher). The catalytic converter also helps NO numbers, and if it's really old, it might need replacement as well. Another way to help reduce NO emissions is to turn back the initial advance a few degrees. Not too many, just like 1 or 2 degrees. This will help.

However, higher octane fuel will hurt his performance and efficiency. That's a fact. It isn't just a waste of money; it's so much more. And sending unburnt fuel into his TWC is not good for it either. Because as it collects exhasut gasses, it gets really hot. Hot enough to burn the fuel. This will kill a catalyst over time. The more fuel dumped, the shorter time it will live.

And I can't speak to octane being a measure of evaporation time. I've never heard of that. But that may be a byproduct of having higher octane, I don't know. But octane is a measure against knock. Plain and simple.</TD></TR></TABLE>

thats the chemistry answer i have been given on many occasions. how do you measure against anti knock? their is no way to explain it because it is caused by various factors other than octane that we as basic car nuts have little understanding of. You can explain whether the gas is sprayed evenly, not creating hot spots, or whether under compression it condenses and burns unevenly, as is described by octane. Another reason why octane isn't plainly stated as anti knock is because carbon build up causes knock more so than octane in non- performance situations.

both definitions are true, but i just prefer the more concrete example of how they used to test octane in the olden days, besides the new fangled hard to understand anti-knock affect they use today. it just makes more sense to me this way.

 

WTF!? different octane fuels dont burn at different rates, furthermore theres no freakin way a higher octane gas is causing anyone to fail smog. something on his car isnt working right, find it and fix it.

 

Right right. Already solved that. My bad. Posting with eyes half closed is very bad and I apologized. And different octane fuels do burn at different rates in relation to cylinder pressure based on cylinder position in its stroke. 89 will burn evenly and smoothly in most 9:1 engines that are tuned to take that form of pump gas. 91 on the same engine will require more pressure to begin burning properly, hence it all tends to go off at the top... so to speak. This isn't very efficient or smooth for making power. The way to defeat 91 from popping off late is to advance your ignition timing to help begin its burn sooner in the cylinder stroke hence causing it to burn more smoothly and evenly.

Someone also said that 89 would actually be worse for his smog issue and that's absolutely correct. When he starts burning more fuel more efficiently, his cylinder temps will only go up. He'll make more power, and also make more NOx. This won't help matters at all for him. However, making horsepower has very little (if not the opposite) to do with passing emmissions or not being a gross polluter against the newest standards.

Snootch, that's some cool ****. I'm going to go read up on that way of defining octane and what properties it brings to light. Plus, the chemistry answer is a comparison between the fuel being burned and an 8 hydrocarbon chain which I believe has a rating of 100 blah blah blah. Basically, it's comparison. But with all the other factors that influence burn in the cylinder, at least its a place to start.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by AzCivic1.6 &raquo;</TD></TR><TR><TD CLASS="quote">something on his car isnt working right, find it and fix it.</TD></TR></TABLE>

Bingo.

Easy fix that will help but may not solve the issue will be to retard your timing a little bit. This will cause combustion to be less thorough which will cause cylinder temps to lower. Not sure how much, but it will help some. Then again, maybe that will raise the HC count some. Maybe. And that's also bad. But, a good tune-up is always a good place to start and then go from there.

 

just one quote of many websites that talk in depth about octane ratings:
"Also, a common fallacy is that higher-octane gasoline burns faster or slower. As octane increases, the components that increase the octane chemically react in the combustion process to merely prevent detonation rather than change the burn rate."

 

"To understand octane rating, you need to understand a little bit about how car engines work.

The engine’s power comes from carefully controlled explosions of gasoline/air mixture inside the engine. To control the explosions, the gasoline must burn at exactly the right rate. This is controlled by the gasoline’s chemical composition.

Gasoline is a mixture of many chemicals that burn at different rates. One chemical that burns at the right rate is isooctane. A chemical that burns too quickly is n-heptane. To describe how fast a gasoline burns, a scale was developed using these two chemicals. Isooctane is defines to have an octane rating of 100, which n-hepatine has an octane rating of 0. Octane ratings compare the burning characteristics of gasoline to mixtures of isooctane and n-hepatane.

For example, if a cheap gasoline burned the same way as a 50:50 mixture of isooctane:n-heptane, the octane rating would be 50. Gasoline with an octane rating of 87 burns he same way that a mixture of 87 percent isooctane and 13 percent n-heptane would burn."

Taken from: http://www.pa.msu.edu/~sciencet/ask_st/101696.html

"Octane?
If you look at the octane rating as only an indicator of what the fuel was designed for, you'd guess that a 120 octane fuel was probably designed for an engine that was prone to "knock" - like an older American V8 with relatively poor cooling and high compression. That fuel will be blended to burn at controllable rate that matches the high pressures and temperatures present AND resist "knock". A good match for those V8 engine conditions.

Burn Rates- That's the ticket!!
If you take that same fuel that worked well in the above V8, and run it in an engine, like a cbr900, with it's lower cranking compression and lower combustion chamber temps, it will, without a doubt, burn much too slowly at those lower temps and pressures and reach maximum cylinder pressure too far after TDC for best power.

Things generally burn slower when they are cooler and vice versa. Peak cylinder pressure will occur much past TDC - decreasing the power produced if you keep the same ignition timing."

Taken from: http://www.factorypro.com/tech....html

"WHAT ABOUT FUELS?


There are six things to consider when comparing hydrocarbon fuels:
1. Volatility. In short, what's the fuel's propensity to vaporize. This effects the ability to easily mix the fuel with air and the fuel's tendency to vapor-lock. It also determines the pollution characteristics of the fuel where evaporative pollution is a concern.
2. Pre-ignition & knock resistance. Referred to as "Octane value." How much energy does it take to get the fuel burning - how much does it resist auto-ignition from compressive heat? Also, what is the rate of burn of the fuel (which affects the rate of pressure rise)?
3. Energy content. How much energy can be extracted from the fuel as a percentage of its volume or mass.
4. Heat of evaporation.
5. Chemical stability, neutrality, and cleanliness. What additives does the fuel contain to retard gum formation? Prevent icing? Prevent corrosion? Reduce deposits?
6. Safety"

Taken from: http://www.prime-mover.org/Eng....html

Maybe everyone is right or wrong... or maybe it's different ways of describing the same phenomena known as pre-ignition versus compression where the compression ratio causes different conditions making it easier or more difficult for all gasolines (regardless of octane) to burn faster or slower.

Or maybe this should be in its own thread and not hyjacking this guy and keeping him from passing smog.


Modified by delScho at 3:59 AM 7/6/2004

 

n-heptane ignites under lower pressures compared to that of isooctane, it doesnt burn too fast it ignites to fast.

and i dont know what the heck that other guy is talking about, saying that the combustion chamber temp of a motorcycle is somehow lower than that of a 4cyl car engine.


Modified by AzCivic1.6 at 6:32 AM 7/6/2004

 

too much to read lol good info guys

 

The more I read into this, the more I'm thinking that it's all the same argument. Put it like this, will something burn faster or slower in different pressure conditions? Different heat conditions? If you look at this in terms of a cylinder moving up and down inside of a block right before ignition, the mixture is being compressed as the cylinder rises, then as the mixture ignites (either by the sparkplug or by pre-ignition) heat is generated and gasses expand causing more pressure. The higher the octane, the more heat and pressure are required to get it burning. By burn rate, I think that it is referring to how fast the mixture combusts given the conditions around it. In the same engine (let's take a D15B7 for argument), with the same ignition timing (barring any detonation), if you ignite (sparkplug ignition) an 89 mixture versus a 91 mixture and they burn at equal rates, then why does that given engine make more power with the lowest octane rated fuel that still resists knock? Because it is burning more thoroughly and faster than the higher octane fuel in that given condition.

And that's the big phrase: "in that given condition". If you change the conditions, then 91 will burn at the same rate as 89. I just think it's highly improbable that they burn at the same rate in the same hole getting the same spark.

And I don't know what that guy was saying about the V8's compression either. Maybe he was referring to the race engines. I don't know. Just something I found (even though his example was poor).

 

good discussion on this, thats why i made the statement in the first place, there really is alot of different information on this subject, and it all comes in handy when looking at all this stuff.

great added info

 

thanks for the info guys. I appreciate it. I'm going to try and figure out whats wrong, change my cat. converter, spark plugs, fix my timing...and as for the fuel...I'll run 89 octane...to see how it runs. Don't think my o2 sensor is messed up, changed it not long ago and no cel comes up. But still more info is appreciated. Thanks.

 

after you fix your timing you only need to run 87.

 

What does it say to run in the owner's manual? I'm sure 87 would work just fine, but for the sake of smog the safe bet is to play it by the books. Honda wrote the fuel and spark maps for a certain octane fuel. It should work its best at that octane rating. But I've never read a manual for a D16 so I couldn't tell you that off hand. Just another thought.