Diesel engines operate at higher compression ratios than gasoline engines, and fuel is injected under much higher pressure. An injection pump, usually driven by a belt or chain linked to the crankshaft, does this by supplying fuel under high pressure (15,000 pounds per square inch or more) to the injectors for each cylinder. As with gasoline engines, diesel injection pumps are controlled by the engine control module in order to deliver the correct amount of fuel at the right time for each cylinder. With diesel engines, fuel is injected directly into the cylinder, while in most gas engines it’s injected into an intake port (though there are a growing number of gas engines with direct injection). Diesel engine pumps can be damaged by sludge and other deposits, they can develop leaks and electrical parts can fail. A worn injection pump will make a diesel engine harder to start and is often accompanied by a loss of power, though a faulty fuel supply pump or dirty fuel filters could also be the cause. They are usually expensive to replace, ranging up to a few thousand dollars. That’s why many diesel owners buy remanufactured pumps or have their original pump rebuilt.
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