Bad gas comes in many different varieties. There is the kind you get when you gulp down a double bean burrito. But not so funny is the kind that comes out of a pump nozzle in filling stations across the country. According to some sources, there is more bad gas out there than the industry is willing to admit - and it is causing a significant increase in driveability and emissions problems for many vehicles.
The two types of bad gas you should be most concerned about (bean burritos notwithstanding) are:
Poor Quality Gas
The main issue with gasoline that fails to keep the fuel system clean is quality (or the lack thereof). To save a few pennies per gallon and increase the competitive margin (or profit margin) of his product, a gasoline supplier may choose to reduce or even eliminate the amount of dispersant-detergent additives in his fuel. Or, he may choose to use a less-effective product or one that causes other kinds of problems.
Commonly used deposit-control additives include polysibutylamine, polyisbutylene succinimide and polyisobutylene phenylamine. But these same additives also can build up on intake valve stems causing them to stick. To prevent this from happening, additional additives called "fluidizers" also must be added to the fuel. But over time, these can contribute to the formation of combustion chamber deposits that raise compression and the engine's octane requirements.
One of the best additives is polyetheramine. It keeps injectors, valves and combustion chambers clean without the help of any additional fluidizers - but it costs more than twice as much as the other commonly used additives.
How much additive does it take to provide an adequate level of protection? Industry sources say the recommended level is about 1,000 parts per million (ppm) of dispersant-detergent in the fuel - which costs the gasoline supplier less than a penny a gallon. Even so, as much as 85% of the gasoline that is being sold contains only one-tenth the recommended dosage, or only 100 ppm of additive. Consequently, bad gas is good for the repair business.
When people use gasoline that does not keep their fuel system clean, their injectors gradually clog up with varnish deposits. Some injectors (mostly the older pintle and nozzle style) are more vulnerable to clogging than others. It is not something most motorists notice right away because it takes time for the deposits to accumulate. But with every drive cycle, the accumulation of deposits gradually restricts the nozzle orifice causing a reduction in fuel delivery.
Deposits also disrupt the normal injector spray pattern, which interferes with fuel atomization and mixing. This results in a lean fuel mixture that may cause the engine to misfire, idle poorly, and hesitate or even stall when accelerating.
It does not take much of a restriction in an injector to lean out the fuel mixture. Only an 8-10% restriction in a single fuel injector can be enough to cause a misfire.
A lean mixture caused by dirty injectors also increases the risk of detonation when the engine is working hard under load.
Lean misfire at any speed increases hydrocarbon emissions that may trigger a misfire code and turn on the Check Engine light on 1996 and newer vehicles with OBD II systems. The code will often be a P0300 random misfire code, or you may find one or more misfire codes for individual cylinders depending on which injectors are affected most.
Use of the proper amount of detergent additive helps wash away the varnish deposits and keeps the injectors flowing normally. Varnish buildup is worse after a hot engine is shut off and undergoes a period of heat soak. During this time, any residual fuel that is in the tips of the injectors evaporates and leaves behind the heavier waxy compounds that form varnish deposits. If the next batch of gasoline that squirts through the injectors when the engine is started does not contain enough cleaner, the deposits will remain and continue to accumulate. Eventually it builds up to the point where it restricts the injector and causes drivability problems. This requires cleaning the fuel injectors.
On four-cylinder engines, the #2 and #3 injectors are in the hottest location and tend to clog up faster than the end injectors on cylinders #1 and #4. The same applies to the injectors in the middle cylinders in six- and eight-cylinder engines. The hotter the location, the more vulnerable the injector is to clogging during heat soak after the engine has been shut down.
Off-car Injector Cleaning
Most high-mileage engines, as well as engines that are mostly used for short trip stop-and-go driving, will benefit from having the injectors (and the intake valves and combustion chambers) cleaned. Cleaning the fuel injectors restores normal fuel delivery and performance. Cleaning the intake valves removes deposits that can obstruct airflow (if thick enough). Intake deposits also can act like a sponge and absorb fuel causing a momentary hesitation when the throttle is suddenly opened. Removing combustion chamber deposits reduces compression and the risk of engine-damaging detonation (spark knock).
Engines that use oil typically have heavy intake valve and combustion chamber deposits that do not respond well to normal levels of detergent in gasoline. Additional cleaner is needed, which can be added to the fuel tank or run directly through the injectors.
Injectors can be cleaned in place or removed and bench-cleaned using special injector cleaning equipment. On-car cleaning is obviously the easiest approach because it requires less labor. If the injectors fail to respond well to cleaning, they will have to be replaced. It is an expensive repair, but one money-saving alternative here is to install "reman" injectors. In most cases, the reman injectors are nothing more than used injectors that have been cleaned and flow-tested.
The benefits realized by injector cleaning will obviously vary depending on the condition of the injectors prior to cleaning and how badly they were clogged. Really dirty injectors should show more of a noticeable improvement in performance than ones which have only a light accumulation of deposits. Either way, performance, fuel economy and emissions should all be better after a cleaning.
To clean carbon deposits from the intake valves and combustion chambers, top cleaner can be used (just follow the instructions), or you can use equipment that is designed to clean the upper engine.
Some experts recommend replacing the spark plugs after doing an on-car injection cleaning or decarbon treatment. The residue that is loosened and washed away by the solvent may increase the risk of plug fouling. Changing the oil and filter is also a good idea following a cylinder decarbon treatment because some of the solvent will get past the rings and end up in the crankcase.
Low-octane gasoline involves a couple of different issues. One is outright fraud on the part of some gasoline retailers and distributors. Most states have a department of weights and measures that makes sure filling station pumps are accurately calibrated so patrons get a full gallon when they pay for a gallon. But most states have no way of policing fuel quality to make sure it meets the rated octane. Consequently, there is a big temptation to sell regular octane fuel at a mid-range or premium price.
Most pumps offer three grades of gasoline: regular (87 octane), a mid-range blend (89 octane) and premium (91 octane). The numbers will vary a bit depending on the brand, the additives used and whether or not the fuel contains ethanol as an octane-boosting additive. A 10% ethanol blend typically adds a couple of points to the base octane rating.
As the octane rating goes up, so does the price. Most pumps mix regular and premium to deliver the mid-range grade. There have been cases where people have tampered with pumps to change the mixture ratios for a more profitable blend. But the more common scam is to simply fill the underground "premium" tank with regular, or to dilute it with a few hundred gallons of lower octane fuel. It is a scam that is hard to detect. Even honest gasoline retailers can be ripped off by distributors who fail to deliver fuel that meets the full octane rating.
Most vehicles do not need premium. A few do specify premium fuel in the owners manual, but these are mostly high-performance turbocharged or supercharged engines. The average vehicle should not need the extra octane unless it has a problem or a lot of miles and a heavy buildup of deposits in the combustion chambers. Then it might be worth the extra 20 to 30 cents more per gallon for premium.
Of course, another valid reason for buying premium is to get a higher level of fuel-cleaning additives, which some grades of premium do contain. That is a purchasing decision the motorist has to make.
The octane rating of the fuel depends on what is in it. Years ago, tetraethyl lead was used to boost the octane rating of gasoline. It was a great octane booster and also helped lubricate the valves to prolong valve and seat life. But lead is a heavy metal that is toxic to people and the environment. Lead also contaminates catalytic converters and oxygen sensors so it cannot be used in modern engines. Now they use methyl tertiary butyl ether (MTBE), which is made from natural gas, and ethyl tertiary butyl ether (ETBE), which is made from corn and natural gas. The higher the level of these additives, the higher the octane rating of the fuel.
"Reformulated gasoline" (RFG) is now required in many urban areas to reduce air pollution. RFG requires extra refining to remove aromatic chemicals, and uses higher amounts of "oxygenates" such as MTBE, ETBE or ethanol alcohol. This raises the cost of RFG 2-10 cents a gallon and reduces its energy content about 1-3%. But the EPA insists the benefits outweigh the trade-offs.
There is some evidence to suggest that RFG does not keep very well if allowed to sit in a vehicle fuel tank for long periods of time (say 8-10 days or more). According to one engine builder, the ingredients separate and absorb water, which can lean out the fuel mixture excessively and cause drivability problems. Vehicles that sit unused for long periods of time, therefore, can benefit from a dose of fuel stabilizer in the gas tank.
Dealing With Detonation
The best way to tell if an engine needs more octane is to see how it performs under load. If it knocks and pings, it needs more octane - or service. Any number of things can cause detonation, including:
If an engine is experiencing detonation, you should always investigate the just mentioned possibilities to rule out any repairs that might be needed. On older engines that have distributors, retarding the timing a few degrees may help reduce or eliminate a detonation problem.
If a performance engine has a lot of static compression (more than 10:1) and/or a supercharger or turbocharger, the only cure for a persistent detonation problem short of reducing compression or limiting boost is to use racing gasoline or an octane-boosting additive. Many octane-boosting additives also contain detergents to help keep the fuel system clean, so there is a double benefit to using this type of product.
Another problem is gas that has been contaminated with dirt, water or other liquids. Many filling station pumps have a filter that keeps dirt and corrosion that has settled in underground tanks from getting into their customer's fuel tanks - assuming they maintain the filters properly. But these filters will not remove water. Alcohol attracts water, and if there is enough water present it can make the alcohol separate from gasoline.
Underground tanks have to meet stringent EPA requirements to prevent fuel leakage and soil contamination. Regular inspections are a must to ensure their integrity. But nothing is perfect and tanks sometimes leak and allow moisture to seep inside.
We have seen vehicles that were misfiring, sputtering and stalling because they had bad gas in their fuel tanks. In some cases the gas was contaminated with water. In others, there was too much alcohol. We have even seen cars that somebody mistakenly filled with diesel fuel. The not-so-funny part is that hours were wasted trying to diagnose the cause. In the end, it turned out to be bad gas. Draining the tank and refilling it with fresh gas solved the problem completely.
It does not happen very often, but fuel also can be cross-contaminated in pipelines, in storage facilities and distribution centers, and even in transit by moisture and other petroleum distillates such as diesel fuel, kerosene (jet fuel) and other chemicals.
The most common cause of dirty gas, though, is the vehicle's own fuel tank. As the miles accumulate, the protective plating inside the tank can wear away allowing corrosion to occur. This obviously does not happen with plastic gas tanks but it is quite common with steel tanks. The small flakes of rust are then pulled into the fuel pickup strainer where they can clog the strainer, damage the fuel pump or plug the fuel filter.
A lean fuel condition combined with lower-than-normal fuel flow and/or pressure is usually a good indication that the fuel system has a restriction - if the problem i not a weak fuel pump. If you check the filter and find it is plugged with debris, inspect the gas tank and clean it or replace it as needed if the tank is full of dirt or corrosion.
Finally, if a vehicle cranks and has spark but refuses to start, check the fuel gauge. No gas is worse than bad gas.
More Fuel System Articles:Fuel Contamination: What To Do If You Put The WRONG Fuel In Your Car
Bad Gas Update
Gasoline Fuel Treatments
Troubleshooting Fuel Gauges
My Advice On Gas-Saving Gadgets
Troubleshooting Electronic Fuel Injection Problems
Fuel System Diagnostics: Finding the Best Approach
Troubleshooting & Cleaning Fuel Injectors
Diagnosing Returnless Electronic Fuel Injection Systems
Fuel Octane Ratings & Recommendations
Troubleshooting & Cleaning Fuel Injectors
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