Injection Pump Won't Pump Fuel

My Injection Pump Won't Pump Fuel

The injection pump on most YM series Yanmar engines is really just several small pumps inside of a single housing. Each cylinder gets its own small plunger that pumps fuel to that cylinder. The plungers ride on the engine's camshaft and, as the camshaft rotates, the plunger is forced up and it pushes fuel to the injector. As the camshaft continues to rotate- the plunger is forced back down by an internal spring, and it picks up more fuel for the next cycle. 

If there is water in the fuel or the engine is run out of fuel completely- those tiny plungers can flash rust. The tolerances of those plungers are very tight, and the rust causes them to stick in the cylinders. The plungers can get stuck in the up position and the internal spring might not be able to force the plunger back down to grab the next load of fuel. 

A GENTLE tap on the side of the injection pump (while cranking over the engine) can sometimes free the little plunger and get it working again. 

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Article ID:
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Date added:
2009-05-19 11:34:45
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