Testing toyota fuel injector Wiring with a paperclip

Using a paperclip you can test the basic operation of gasoline fuel injectors.

NEVER DO THIS TEST WITH A RUNNING FUEL PUMP IT WILL INJECT FUEL IN THE CYLINDERS.DISABLE FUEL PUMP FIRST

this information is targeted at TOYOTA designs but should be meaningful for many other makes.

this test can reveal:

• the injectors cannot be actuated by the ECU(if you can't manually it cannot either)
• one or many injector are clogged (don't click when powered)
• the injector you are actuating is matching the one that is  clicking, (in custom engine swaps those injector wires can be inadvertently exchanged)

this test cannot reveal:

• current applied at the positive pin of the injectors is sufficient(too low current caused by bad resistor pack or bad wires on the 12v side)

So overall it can tell you that if you can't actuate the injectors manually the ECU wont be able either...

It can be performed on a car or a bench test setup. The following video shows it on a bench setup.

Theory behind the test

On conventional designs, the fuel injectors have 12v current applied on their positive pin when the ignition switch is ON. the negative pin of each injectors is connected to an ECU which sinks that current when the ECU wants to actuate that specific injector.

Without an ECU installed but having the ignition switch at ON you can sink an injector current manually by jumping an injector contact at the ECU connector with a main ECU ground contact  at the ECU
connector. doing this will result in a clicking sound coming from that particular injector when the jumper is placed or
removed.