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Old 07-31-2015, 02:34 PM   #13
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Originally Posted by FlyWright View Post
Keep in mind that FL120s require an oil change in the fuel pump every 50 hours. I don't think the FL135s require this. Ford Lehman owners, is this correct?
Yes it is.

The injection pump on the FL120 is self-lubed; it has its own lube oil sump. Its the nature of this kind of injection pump (called jerk injection) to gradually wear down the plungers and the walls of the bores they go up and down in. As the wear increases, more and more fuel can leak down past the plungers into the lube oil below. The lube oil only lubes the pump's drive mechanism. The plungers themselves are lubed by the fuel they are sending to the injectors which is why for this type of injection system fuel lubricity is critical.

As the fuel leaks into the lube oul it dilutes the oil and it becomes a less effective lubricant. To ensure the lube oil is always doing the proper job of lubricating the pump's drive mechanism even with a fair anount of leak down and dilution the oil change interval of 50 hours was selected.

The FL135 is also a jerk injection engine. However being a somwhat newer design than the FL120 Ford figured out how to lube the pump's drive mechanism using the engine's lube oil. So leak down still occurs and gets worse with time, but now instead of diluting a half a quart of lube oil it's diluting three gallons or so. So the engine's specified oil change interval is sufficient to deal with it.

The FL120 also has an automotive-type fuel pump that sends fuel to the injection pump. As on an automotive engine, this fuel pump is driven by the camshaft and is lubed by the engine's lube oil.
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