Leave the engine idling.
With the engine running, use a stethoscope to check each injector for valve operating noise. Valve clicks indicate the valve is opening and closing.
If a stethoscope is not available, the presence of injector valve operating noise can be felt with a screwdriver or finger.
If there is no noise or it is uncharacteristic, it is necessary to check the supply voltage, resistance and tightness of the injectors.
Checking the supply voltage and resistance
Check the supply voltage. To do this, disconnect the plug connector of the valve injector and connect the test lamp on the semiconductor diodes to the contacts of the plug of the supply wires. Ask the assistant to turn on the starter. The test lamp should blink.
If the indicator lamp does not flash, the cause of the malfunction may be a broken wire or the control unit itself.
Turn off the ignition.
Connect an ohmmeter between the contacts of each valve injector and measure the resistance. If the resistance of any injector differs from the other values, replace the defective valve injector.
Checking for leaks
Remove the fuel manifold complete with valve injectors and attached fuel hoses.
Connect the plug connectors of the valve injectors.
Insert the valve nozzles into a suitable measuring container.
Ask an assistant to turn on the starter for a few seconds. The valve injectors should intermittently inject fuel in accordance with the firing order of the cylinders. Compare the shape of the fuel jets of the valve injectors. The fuel jet from all injectors should have the same conical shape.
Turn off the ignition.
Disconnect the plug connectors of the valve injectors.
Turn on the ignition for about 5 seconds, do not turn on the starter. Now check for leaks: no more than one drop of fuel should come out of the injector nozzles within one minute.
Install the valve injectors.
[The original article is posted at fordbook]