There are two sets of trigger points in the lower part of the distributor. When each set of points opens and closes it triggers three injectors. So if you have three injectors that work and three that don't, it is a near certainty that the problem is with one of the two trigger points. A common problem is that the fenolic (sp?) cam followers on the trigger points (just like ignition points) wear down until the points no longer open. The stationary half of each set of points can usually be tweaked with needle nose pliars such that the contacts will once again open as they should.

If you look down low on the distributor, you will find where a 3-wire connector attaches to the trigger points. The center pin is common to both contacts, so you want to check for continuity first between the center pin and one side pin, then the center pin and the other side pin. Trigger point timing is not at all critical - as long as they do open and close. I always shot for about 180 degress of open and 180 of closed. (That's 180 degrees of distributor rotation which equals 360 degrees crankshaft rotation.) Anywhere in the ballpark is good.

I always found it easier to pull the distributor out and do all this on the work bench.