Re: vac switch
You asked "Would a failing vro pump shoot in too much oil??" Yes, it could, then you said/asked "My concern is that if the pump is pumping too much oil does it necessarily mean that the pump is malfunctioning??". The answer is no, not necessarily. <br /><br />In order to function correctly, the pump must meter a specific volume of fuel to a pre-set volume of oil. The fuel pump and air motor determine the fuel volume. Since liquids (in this case fuel) cannot compress, there must not be any air leaks or restrictions before the fuel pump. Restrictions cause the fuel to "boil" or "vaporize", in effect creating air bubles in the fuel stream. Once aerated fuel enters the fuel pump chamber, the air compresses from the forces of the diaphragms in the fuel chamber and air motor. This allows the pump to "trigger and reset" too soon. This mixes our "preset" amount of oil with "not enough" fuel - in effect over-oiling.<br /><br />Good techs will use a piece of clear hose with a vacuum gauge teed into it (3/8' i.d. in your engine's case), to look for air bubbles in the fuel system. Typically starting at the fuel pump inlet and working back towards the fuel tank if necessary. For example, if you see a stream of small bubles in the hose right at the fuel pump inlet, and then connect the clear hose to the fuel inlet fitting on the lower motor cover, you would know there's a fuel restriction or air leak between the fuel pump and the fitting on the lower pan. Keep in mind an air leak doesn't necessarily leak fuel. <br /><br />Then there are the pump tests we mentioned in your earlier post. Start with the oil consumption test and follow the directions in the service manual (don't know if Clymers or other manuals list this test - if not let me know, I may be able to help by faxing a few pages your way).<br /><br />Keep us posted...<br /><br />-John
