Gasoline quality is an ongoing concern for motorists. The quality of the fuel that goes into your car or truck depends on how the fuel was refined, the additives in the fuel, and the handling and storage of the fuel. Gasoline must meet certain minimum octane requirements to burn normally without causing detonation (spark knock). Gasoline must also be formulated to meet regional air pollution requirements so it will burn cleanly. The fuel must also contain additives that prevent rust and corrosion inside the fuel system, and additives to keep the fuel injectors, intake valves and combustion chambers free of varnish and carbon deposits. If a fuel does not meet all of these criteria, it can cause problems in your vehicle. The same rules apply to diesel fuels (including Biodiesel). Diesel fuel must meet cetane requirements for good combustion, contain the proper lubricants to protect the high pressure injection pump and fuel injectors, and additives to prevent rust and corrosion in the fuel system. We continue to hear complaints about driveability issues that are typically caused by a build-up of varnish deposits in the fuel injectors and throttle body, and carbon deposits on the intake valves and in combustion chambers. These problems include engine knock after cold start or when the engine is working hard under load, hesitation problems when accelerating, rough idle, poor fuel economy and even misfiring (which may cause your Check Engine light to come on). GASOLINE DEPOSIT FORMATION When deposit control additives are not adequate in gasoline, harmful deposits can build up inside the engine: * Fuel varnish deposits that form inside the injectors restrict fuel delivery and cause the engine to run lean. This may cause lean misfire, rough idle, hesitation, poor fuel economy and increased HC emissions. A lean fuel mixture also increases the risk of detonation and preignition. These deposits tend to form during the heat soak period that occurs after the engine is shut off. The shorter the trips and the more frequent the drive cycles, the faster these deposits buildup. * Deposits that form in the throttle body can reduce airflow through the idle bypass circuit affecting idle quality and smoothness. These deposits are formed by fuel vapors that rise up through the intake manifold. Intake valve deposits from gasoline that does not contain enough detergent * Deposits that form on the intake valves can restrict airflow through the intake ports, causing a loss of high speed power. The deposits can also act like a sponge and momentarily soak up fuel spray from the injectors. This disrupts the mixing of air and fuel causing a lean fuel condition, hesitation and reduced performance. Deposits can also cause valve sticking and valve burning. Intake valve deposits are formed by normal combustion byproducts, but may build up more rapidly if the valve guides or seals are worn and the engine is sucking oil down the guides. Dirty intake valves are a common problem on late model engines with Direct Gasoline Injection (GDI) because the fuel is sprayed directly into the combustion chambers rather than the intake ports. Consequently, there is no fuel spraying on the backs of the intake valves to wash away deposits. Oil vapors that are siphoned back into the intake system via the PCV system can stick to the intake valves and create carbon deposits. * Deposits that form inside the combustion chamber and on top of the pistons increases the compression ratio of the engine and the octane requirements of the fuel. Too much compression can cause spark knock (detonation) if the fuel's octane rating isn't high enough. Over time, detonation can damage the head gasket, piston rings and rod bearings if it is not controlled. The knock sensor will detect detonation and tell the PCM to retard spark timing. This will take care of the knock, but retarded timing also increases fuel consumption and emissions. A build up of carbon deposits inside the combustion chamber also increases the risk of hot spots forming that may cause engine-damaging preignition. The hot spot ignites the fuel before the spark plug fires, causing a sharp rise in combustion pressure. Under extreme conditions (high rpm and load), preignition can burn a hole right through the top of a piston! A condition known as Combustion Chamber Deposit Interference (CCDI) can also occur when the carbon deposits are so thick the deposits on the piston and head make physical contact. This area, known as the Squish Area (piston to top of chamber), has a clearance that is about as thick as a paper clip. This can cause a loud, metallic banging sound when a cold engine is first started. The deposits are soft and will gradually flake off. But the flakes may lodge between the valves and seats causing a loss of compression, misfiring and rough running when the engine is cold (a condition called Combustion Chamber Deposit Flaking or CCDF). KEEPING FUEL INJECTORS AND COMBUSTION CHAMBERS CLEAN The formation of harmful deposits can be controlled by adding detergent-dispersants to gasoline, the most common of which is polybutene succinimide. Used with a petroleum carrier oil, detergent-dispersants help keep the intake manifold and ports clean. These chemicals are more effective than the carburetor detergents that were once used in gasoline, but they must be used at concentrations that are three to five times higher than the older carburetor detergents. Deposit control additives such as polybutene amine (PBA) were introduced in 1970 to help keep injectors and intake valves clean. The only drawback with PBA is that too much of it can increase combustion chamber deposits. Polyether amine (PEA), by comparison, cleans fuel injectors and valves, and does not increase combustion chamber deposits. In fact, it helps remove accumulated deposits inside the combustion chamber to reduce the risk of spark knock. In 1995, the U.S. Environmental Protection Agency set minimum standards for additives in gasoline to prevent the formation of deposits in fuel injectors. Gasoline refiners had to certify their additive packages met these standards, but some experts now say the original standards were set too low and do not provide adequate protection with some fuels and engines. The minimum EPA required level is referred to as the "Lowest Additive Concentration" (LAC), and is typically found in the cheapest priced gasoline. TOP TIER GASOLINE At the other end of the fuel quality spectrum are "Top Tier" gasolines. These fuels are recognized by the vehicle manufacturers as having the most effective additives and in the highest concentrations. Gasoline retailers must meet the high Top Tier standards with all their grades of gasoline (not just premium) to be designed as a Top Tier supplier. In addition, all the gasoline outlets carrying the brand of approved gasoline must also meet the same standards. Gasoline retailers who are currently on the Top Tier list include Chevron, Chevron-Canada (B.C. only), Texaco (Chevron supplied only), Conoco, Entec Stations, Esso, ExxonMobil, Kwik Trip/Kwik Star, MFA Oil Company, Phillips, QuikTrip, Road Ranger, Shell, The Somerset Refinery and 76. For a complete listing of gasoline retailers who are selling Top Tier gasoline, Click Here. Top Tier gasoline brands. POLICING GASOLINE QUALITY Unfortunately, fuel quality isn't something that is easily policed. Many states have programs in place to monitor fuel quality on either an ongoing basis or "incident specific" basis. Most are run by the state's Department of Weights and Measures. Even so, the focus of most of these programs is to make sure consumers aren't being cheated at the pump and get the full gallon they pay for. Some programs also check fuels to make sure they do not contain too much alcohol. The specific density of gasoline can be field tested to determine its volatility and alcohol content. But testing octane and the amount and type of additives in the fuel requires expensive laboratory testing. So this type of quality testing is rarely done. According to one leading gasoline retailer (who sells a Tier One fuel, by the way), many gasoline marketers have reduced the concentration of fuel additives in their fuel up to 50% in recent years! Most gasoline refiners don't want to sell the public bad gas because they obviously want repeat customers. Even so, they also know that deposit formation is a gradual thing that occurs over time. So if they cut back on the additive package to save a few cents per gallon, nobody is the wiser — and least not right away. The problem occurs when people buy the cheapest LAC gas they can find every time they fill their tank. The low level of additives (or low quality additives) in the fuel will not be adequate to keep their engine clean, and sooner or later they'll start to experience drivability problems. Worse yet, if a bad batch of fuel leaves a refinery and ends up in people's vehicles, it can cause even more serious problems. There have been instances where too much residual sulfur in a bad batch of gasoline has caused a rash of fuel pump failures. Immediate drivability problems may also occur if the fuel is contaminated with water, contains too much alcohol or the wrong type of alcohol (methanol instead of ethanol). Alcohol is a great octane booster, but for ordinary gasoline the amount of ethanol should not exceed 10% (or 5% for methanol). The only exception here is E85 fuel for "flex-fuel" vehicles that is 85% ethanol and 15% gasoline. E85 contains less energy per gallon than gasoline and runs leaner, so the vehicle must have a special fuel sensor so the PCM can compensate for the alcohol to maintain the proper air/fuel ratio. REMOVING FUEL SYSTEM DEPOSITS When a vehicle is experiencing deposit-related drivability, performance or emissions problems, the deposits obviously have to go. The troublesome deposits can be removed a variety of ways. One cost-effective solution to deposit-related drivability issues i…

Fonte: AA1Car.com