what is thedifference between saturated and peak and hold fuel injectors

 

It's how the ECU needs to control them. A saturated injector gets fed the full current and full 12 volts from when you start it opening until it closes. A peak and hold injector is one that gets fed a short burst of peak current to make it pop open, then the injector control feeds it a reduced amount of current to hold it open. Injector resistors can often let you drive peak and hold injectors as if they were saturated, although this makes them open more slowly.

You can tell the difference by measuring their resistance with a multimeter. Most saturated injectors are between 12 and 16 ohms, and most peak and hold ones are between 2 and 4.