Here's my suggestion, along with the other good ones:
Start with light leg extensions, nothing to failure, for 3-4 sets of 10-15 reps. Then hit Leg Press for about 6 sets total, doing
If you can't make 6 reps, go back down to 5, but stick to the heavier weights until you CAN do a good 4-6 sets of 12-15 reps. Don't go lighter for any reason, that's not going to make you're muscles grow. A burn is one thing, but shear force on the muscles (heavy weight
) is another!!
The only reason you should go lighter, is if you're pyramid'in on the last set!
Next, finish off with the leg curls. Again, going heavy as possible.
As for the push on day 1, and pull on day 2, that's an ok plan, and actually works well for some people. So when what you're doing now fails, try it out and see what you think. Nothing.... go back to your old plan, or try something else.