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Fuel System Service
A fuel system service, sometimes called fuel injection service, or "injector cleaning", is a maintenance procedure that is important for fuel injected vehicles. There are many myths surrounding the effectiveness and purpose of this service, and the procedures and machines used can vary. The purpose of this article is to clarify what it is that a Fuel System Service performed by Fleet Service Northwest does for a fuel injected engine.
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Reasons for a Fuel System Service
As a fuel injected engine runs, the electric fuel pump delivers a constant supply of fuel, which passes through a filter before reaching the engine. The pump wears over time, and contaminants in the fuel clog the fuel filter. As the fuel flows through the fuel rail and injectors, deposits form. This can cause low fuel flow through the injectors, or cause the fuel injectors to leak. These conditions will reduce efficiency and may cause emissions failures and damage to catalytic converters. Combustion causes carbon buildup in the intake manifold, on the intake and exhaust valves, in the combustion chamber and on the top of the pistons. Engines with Exhaust Gas Recirculation (EGR) are particularly susceptible to carbon buildup, especially in the EGR passages and valve. Carbon buildup can absorb fuel, causing an engine to run less efficiently. Excess buildup on top of the pistons may cause a knock, particularly on cold start-up. Excessive buildup in the EGR system can cause emissions failures due to insufficient EGR flow. Insufficient EGR flow may also cause pinging. It is important to note that an injector that is completely blocked, or an EGR system that is severely restricted by carbon buildup cannot be cleaned with a Fuel System Service. Cleaning EGR passages manually and replacing clogged injectors can be very costly, so maintaining them with a Fuel System Service is a great preventive maintenance step before its too late.
Performing a Fuel System Service
Diagnostics
The first segment of our Fuel System Service is diagnostics. The first test performed is a fuel flow rate test. A flow rate which is too low usually indicates a clogged fuel filter, although it can be a sign of a weak fuel pump, or a plugged or kinked fuel line. The fuel collected during this test is stored for later use in the fuel system service. Next, a fuel pump deadhead pressure test is performed. This test blocks off the fuel return, and measures the maximum pressure which the fuel pump is capable of producing. Low deadhead pressure is usually a sign of a weak fuel pump, although if combined with an extremely low flow rate, may be an additional sign of a clogged fuel filter or other restriction. The final test is a pressure leakdown test. The fuel rail is isolated and pressurized, and fuel pressure is monitored for several minutes. An excessive drop in pressure can be a sign of leaking injectors, or a damaged fuel pressure regulator.
Soak Cycle
Upon completion of the leakdown test, a fuel system cleaning solution is added to the fuel that was collected during the flow rate test. The fuel/cleaner mix is then flowed through the fuel rail and back to the storage tank on the machine in a continuous loop. This flow thoroughly mixes the cleaner with the fuel, and cleans deposits from inside the fuel rail. As the cycle runs, the return line is momentarily blocked and rapidly opened several times a minute. This causes the pressure in the fuel rail to rise, then drop rapidly. This sudden drop in pressure causes deposits in the upper screens in the injectors to be lifted out. This cycle is typically run for 20-25 minutes. In cases where severe deposit buildup is suspected, the fuel/cleaner mix may be allowed to sit overnight before continuing to the Engine Service step.
Engine Service
Upon completion of the soak cycle, the engine service cycle is started. The machine supplies fuel to the fuel rail, and the engine is started and run on the fuel/cleaner mix. Fuel flowing from the fuel pump is looped back directly to the vehicle's fuel tank, so that it does not dilute the fuel/cleaner mix. As the engine runs, the cleaner erodes deposits from inside the fuel injectors, and dissolves and soaks into carbon buildup from the injector nozzles, as well as from the tops of the pistons, combustion chambers, and valves. On engines equipped with Exhaust Gas Recirculation (EGR) valves, the valve is manually opened periodically throughout the service. Since most of the cleaner is not burned by engine combustion, opening the EGR valve allows the cleaner in the exhaust to flow through the EGR passages and the EGR valve, which are all highly susceptible to carbon buildup.
Post-Service
After completion of the Engine Service, the machine is disconnected from the vehicle and all fuel lines are reconnected. If the fuel filter was determined to be plugged, it will be replaced at this time. If the fuel pump was determined to be weak enough to cause driveability concerns, it may be replaced after consulting the customer. The vehicle is then driven to clear the fuel system of leftover cleaner, since it may cause the engine to temporarily run rough. The cleaner that soaked into the carbon buildup continues to dissolve some of this carbon as the vehicle is driven. Once the technician is satisfied the cleaner has been sufficiently cleared and the fuel system service is complete, the fuel lines are reinspected for safety.
Summary
As you can see, a fuel system service can be a great preventive maintenance step, and can repair some minor problems. It is certainly not a cure-all, and I hope this information helps drivers understand its strengths and weaknesses in a better manner than a TV commercial or flyer attempting to sell these services.
To comment on this and other articles, visit our blog at fleetservicenorthwest.spaces.live.com/blog