I'm afraid this isn't good advice. For two reasons.
1. The OP doesn't specify what ship he's using, if his ship cannot outrun the NPC then 4 PIPs to engines is a waste of time from the outset. OP Press the "target hostile" button to automatically target who's interdicting you as you get interdicted, then submit. If it's a Clipper or a Cobra and you're a T7 then you won't escape by running. 4 PIPS to shields, 2 PIPS to eng every time! Low wake or high wake depending on whether you're mass locked by a larger ship.
2. Even if you are going to run, 4 PIPs to engines
makes less difference than you might initially think to how fast you're able to get away. At the very least you should be starting off with 4 PIPs to shields while you're in the max damage zone of the NPCs weapons (0.5-2km). Once your outside this zone, you've started to take less damage and you're running out of capacitor you can start to put pips in eng again. Putting 4 pips to eng straight away does not in fact increase your speed at all while you still have capacitor left.
Remember 4 PIPS to shields in the first instance no matter what the situation! You will not have the satisfaction of boosting quite as often after a while, but your overall speed will not be greatly slower and your shields will be 2.5x stronger.