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merc 150 xr4 v6

You are asking a couple of different questions there.

Firstly. The oil pump can be checked as follows:

locate the "clear" line from the oil pump that feeds the fuel pump and disconnect it at the fuel pump connection.
plug the fitting on the fuel pump during the test.
mix up some 50:1 premix (gas/oil) in a portable tank and run the motor for 3 minutes.
collect the oil that comes from the clear oil pump line in a graduated cylinder (beaker/test tube that has "cc" markings).
you should get 8.2 cc's of oil (plus/minus 10 percent - so say 7.4 to about 9 cc's of oil) out of the clear tube in 3 minutes at idle speed.

Easiest way to bypass the oil pump is with a bit of tubing. Simply connect the oil pump "in" and the oil pump "out" fittings with the tube. If you fill the tube with oil the pump will happily pump the oil through itself forever. Don't forget to plug the fitting where it used to feed the fuel pump, then mix your gas 50:1.

You can remove the oil resevoir if you so choose. You can also pull the oil pump out completely and remove the drive gear that extends into the block, but you must cover the hole that is left. On that particular model you may or may not be able to get a plate to cover it (the hole where the pump was) from Merc - alternately, you could fashion something up yourself (leaving the pump in place is usually the easiest option).

Now you have to make the decision for yourself whether or not to use the oil injection if it's working or repair and use it if it isn't.

The biggest myth amoungst outboard owners, "mechanics" and techs is that oil pumps fail regularly and blow up motors. With the exception of "autoblend" systems that is simply not true. Lack of maintenance, clogged carbs/injectors and old gas cause the majority of engine failures. A bad oil pump will NOT kill a single piston/cylinder. If the oil pump fails, all the cylinders will be fried equally (have never personally seen that).

Also, these motors were designed to run with a variable rate of oil (between 100:1 and 50:1) depending on the demand of the engine. In the long run, continuing to use the oil injection will save you money on oil and sparkplugs and will help cut down on "cooties" in the cylinders - you have no choice but to "premix" at 50:1 since the engine requires that "sometimes".

But if your stomach sinks every time you start the engine "wondering" if the oil pump is going to "fry your motor", then bypass it and mix away.

(personal note - I run a 1986 140 Evinrude with OMC's VRO oil pump system. When it went a few years back (alarm went off and I shut it down without damage) I dropped the 350 bucks for a new one and hooked it back up - I would not run an outboard on premix if it has the capacity to operate with oil injection, however, if you take a poll you will get very strong opinions on both sides of the arguement. Have to decide what works for you...)
 
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