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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / November 2005will adding ethanol fix my emissions?
Ethanol blended fuel is said to result in improved emissions compared to regular gasoline. Now i wonder when i fuel up to say, a 20% Ethanol blend (some regular/E10, some E85) before going to the emissions test, will i have better chances of passing? Especially of interest would be the CO-percentage, whether it is lower than before. I thought dry-gas would help me once.... ruined my numbers..... my.02 > Ethanol blended fuel is said to result in improved > emissions compared to regular gasoline. [quoted text clipped - 5 lines] > Especially of interest would be the CO-percentage, > whether it is lower than before. First of all what car is this?, OBD11 vehicles are a different issue for emissions, did you or do you have a problem now with this issue, need more info here for any kind of intelligent help. > Ethanol blended fuel is said to result in improved > emissions compared to regular gasoline. [quoted text clipped - 5 lines] > Especially of interest would be the CO-percentage, > whether it is lower than before. It's a 92 Cadillac STS, so i don't think it has OBD yet. It does have various monitoring systems, and is able to display O2 and MAP sensor readings on the display in diagnostic mode. The trouble is, my CO readings got closer to the limit with every emissions test over the years. Ahead of the last test, i thought i'd rather install a new catalyst just to be sure, but it didn't give me a good margin, and didn't even change the trend. I still passed the test, but the CO was one step short of failing. Here's the CO readings during idle 650 rpm: this year (with new cat): 0.45 2 years ago: 0.40 4 years ago: 0.15 6 years ago: 0.09 max. CO: 0.50 Everything should be tuned up well. I checked ignition timing to be within specifications, spark plugs aren't that old either. One trouble i do know of is excessive heat while idling, always close to or displaying a "enginge hot" warning message. The reason for that is known (cooling system issues), i just wonder if a hot engine can have bad emissions for some reason. Also i wonder, can higher idling rpm have a bad effect on the CO-value? Are lower rpm always causing lower CO? forgot to tell: O2 sensors were replaced with the catalyst, too, all new OEM parts. > It's a 92 Cadillac STS, so i don't think it has OBD yet. In fact, it does. OBD started in the mid-'80s, and all '92 US-market cars have it, including your Cadillac. > The trouble is, my CO readings got closer to the limit with every > emissions test over the years. OK...find and fix the problem! > Ahead of the last test, i thought i'd > rather install a new catalyst just to be sure Don't replace parts "just to be sure". Replace parts that are indicated as faulty by means of proper diagnosis. This "add alcohol to cheat pass the test" idea is schlock. Fix the damn car! If you lack the knowledge and tools to do it yourself -- a spark plug wrench is no longer sufficient -- pay to have it done. DS > Ethanol blended fuel is said to result in improved > emissions compared to regular gasoline. [quoted text clipped - 5 lines] > Especially of interest would be the CO-percentage, > whether it is lower than before. Complicated issue. ethanol results in less of some emissions, more of others. However, CO is one that it indeed improves. > Complicated issue. ethanol results in less of some emissions, more of > others. However, CO is one that it indeed improves. How about high octane gas? I didn't use it since i always noticed less mileage with premium fuels. Isn't it then higher emissions for the same rpm because more fuel is burned? Make sure the cat is lit up during the test, if let idle too long this is a problem, also fuel contaminated oil can affect co thru the pcv system ,make sure also the pcv is clean and or new. >> Complicated issue. ethanol results in less of some emissions, more of >> others. However, CO is one that it indeed improves. [quoted text clipped - 3 lines] > Isn't it then higher emissions for the same rpm because more fuel is > burned? > Make sure the cat is lit up during the test, if let idle too long this is a > problem, also fuel contaminated oil can affect co thru the pcv system ,make > sure also the pcv is clean and or new. What effect if any could exhaust system pressure/reduced flow have. There was a different muffler installed before the test and there might also be some crimping of pipes that restricts the flow. About catalysts: can't someone that fails the smog test just install TWO catalysts in his vehicle and it will literally _knock_ the values down? I read that GM was using auxiliary catalysts in corvette engines to keep them within emission limits in California. If you have an epa approved fairly new cat that should be enough, the key here is it has to be hot to be efficient, prolonged idle can negate this.The engine should be scanned to make sure the o2 sensor is working properly and there are no unusual issues with lt/st fuel trims, or block learn on the older cars. >> Make sure the cat is lit up during the test, if let idle too long this is >> a [quoted text clipped - 12 lines] > I read that GM was using auxiliary catalysts in corvette engines to > keep them within emission limits in California. > If you have an epa approved fairly new cat that should be enough, the key > here is it has to be hot to be efficient, prolonged idle can negate this.The > engine should be scanned to make sure the o2 sensor is working properly and > there are no unusual issues with lt/st fuel trims, or block learn on the > older cars. The engine had been run for 10-20 minutes before the test, it's true though that ahead of previous tests it was cranked more intensively. Suppose there was a screw with the rpm during the testing. What would the CO % be at a higher-than-normal idling rpm? At 2800rpm, the CO value goes down, as there is also a lower max value for this speed. The difference is also the EGR valve allowing more exhaust to recirculate at higher rpm. > If you have an epa approved fairly new cat that should be enough ...IF the engine is running properly. If it is not, then the catalyst won't compensate. > ...IF the engine is running properly. If it is not, then the catalyst > won't compensate. Maybe the catalyst is supposed not to compensate any much during idle - because of the lower temperatures. The CO limits are higher for idle than for high rpm, i wonder if this could be the reason. >>...IF the engine is running properly. If it is not, then the catalyst >>won't compensate. > > Maybe the catalyst is supposed not to compensate any much during idle - > because of the lower temperatures. The CO limits are higher for idle > than for high rpm, i wonder if this could be the reason. There are other reasons too. The ratio of cool surface area (quenching area) to the volume of fuel air mixture is far higher under idle, so the surface walls quench the combustion more effectively. More of the charge is cooled and combusts incompletely. The amount of heat energy generated in each cycle is proportional to the volume (actually weight) of charge, but the cooling surface area is independent of charge volume/weight. |
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