Does anybody have useful tips for checking the fuel injectors in a multi-port system?

Checking them for what? Their is a device called a noid test light kit. They plug in directly at the injector and you can check the electrical impulses.

Otherwise, it takes specialized equipment to test the individual injectors outside of the engine. It can test the internals of the injectors, flow pattern and flow rate.

With multi port, injectors 2&3, are paired together(fire at same time), 1&4 are paired together......each injector should measure 12 ohms.....if one is shorted, it can draw too much current, and the injector driver for BOTH injectors will disable both injectors....