Auto Service World
Feature   March 1, 2011   by Chuck Carman, Curriculum Developer CARS

When Good Is Not Good Enough

iagnosing intermittent misfires can be difficult. There are a wide variety of conditions that can be the source of the concern. With so many possible scenarios affecting proper combustion, it just seems unfair when clean fuel must also be...

iagnosing intermittent misfires can be difficult. There are a wide variety of conditions that can be the source of the concern. With so many possible scenarios affecting proper combustion, it just seems unfair when clean fuel must also be suspected—but nobody said being a technician would be easy.

Since 1995, the Environmental Protection Agency (EPA) has established fuel additive standards. These additives include demulsifiers, metal deactivators, antioxidants, corrosion control and detergents. Additives are used to improve emissions by improving engine performance. However, the established additive specifications levels have not been adjusted since then.

Unfortunately, fuel suppliers have actually reduced some of the detergent additive concentration levels of their gasoline to a point where there is almost no Deposit Control Additives (DCA) present in some samples. This has lead to an increase in engine deposits which has hindered the ability of a vehicle to maintain the strict Tier 2 emission standards. The reduction of these additives can increase emission levels and create drivability concerns.

While engine manufacturers have developed many advancements to further improve performance and reduce emissions, this reduction of fuel additives has worked against some of these improvements. The introduction of returnless fuel systems has lowered emissions by not returning hot fuel back to the fuel tank. However, by not having a return fuel line it is much easier for fuel contaminants to collect forming deposits in the fuel rail, injectors and on the intake valves, causing misfires, increased emissions and other drivability concerns. Many times, the issue these deposits create are intermittent and will only be experienced during very specific driving conditions, such as turning in one direction or acceleration or deceleration, making diagnosis of this condition more difficult to isolate.

Six of the world’s top automakers have recognized that the current EPA minimum detergent standards are not what is needed for their current level of high-performance, low-emission producing engines. They have set a higher standard for gasoline performance. They call this “Top Tier” gasoline and published the standards for the various gasoline retailers to voluntarily meet. This blend of fuel has enhanced detergents and no metallic additives. In fact, detergent levels for Top Tier fuel can be 2.5 to five per cent higher than the minimum EPA standards and the Canadian General Standards Board. The use of gasoline manufactured to this standard can have a noticeable improvement on engine performance and emission reduction.

Unfortunately, not all gasoline retailers carry the Top Tier fuel. Retailers must offer Top Tier fuel in all grades to become approved by the automakers. A list of gasoline retailers that meet this standard in Canada and the United States can be found at

This means a customer may be purchasing clean fuel from a retailer and inadvertently contaminating their fuel system due to the fact that these enhanced detergents have not been added. Many times, if the concern is intermittent, taking a fuel sample may not clearly show the contamination. It may be necessary to carefully remove the fuel rail, ensuring that the fuel within is not lost, so it can be closely inspected in a clean container. The inside of the fuel tank may also need to be closely inspected for deposits.

If found, the entire fuel system must be flushed. This means purging the fuel rails and injectors of any deposits following the manufacturers’ recommendations. In extreme cases, the injectors may need to be replaced if chemically cleaning them can not correct the internal restriction. It also means removing and having the fuel tank properly cleaned, not just drained. If it is only drained, the condition will return in as little as a few hundred kilometres.

If the fuel system has been exposed to contamination for an extended amount of driving time, some of the deposits will pass through the fuel system and collect on the intake valves. This build-up of debris can cause the stems of the valves to bind and stick, causing further performance problems. If the damage has managed to develop to this extent, further repair will be needed. In many cases, the valve stem deposits can be chemically cleaned without having to disassemble the cylinder head. In severe cases the valves and possibly the cylinder head may not be serviceable and will require replacement.

If fuel contamination is determined to be the cause of the drivability concern, advise the customer to purchase fuel from high-volume retailers that sell Top Tier gasoline to keep from experiencing a repeat condition.

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