This is a awesome test because it can be done very fast using a very inexpensive tool called a Noid light. This test will tell you if the computer is pulsing the fuel injectors open when cranking the engine over. Most of the time this test is done when the engine is cranking over but not starting. However, you can do this test when the engine is running to see if a certain fuel injector is getting a signal to fire if the engine seems to be misfire for some reason. Below is a picture of my Noid light set.
Here is a picture of the Noid light I use most of the time.
Here is a quick video on how to check fuel injector pulse using a Noid light.
Again, you can do this test within about 10 minutes provided that the fuel injectors are easy to gain access to. This test is fast, easy, safe and I have found it to be very reliable.
Here is a picture showing the noid light plugged into the injector connector when checking injector pulse a 2002 Ford Taurus. This one came in on the hook (tow truck) and was a crank no start. When cranking it over, the engine had spark, the Noid light was blinking but it the engine did not did not have fuel pressure. I installed a new fuel pump to get it up and up and running. The Noid light was a big help in diagnosing the crank no start condition.
Here I am checking injector pulse a 1992 Chevy truck. This particular truck would start and run just fine at first, but would not start back up after turning it off and letting the engine sit for about 20 minutes (hot soak). During this time when it would not start back up, it would lose injector pulse and spark. We replaced the distributor and the ignition control module and it was good to go!
Here are some quick tips on how to use Noid lights.
1) If the Noid light stays on with the key on or when cranking, chances are wiring on the ground side of the circuit is either shorted out (shorted to ground) or the driver inside the computer is bad and the computer may need to be replaced.
2) If the Noid light does not blink at all when cranking the engine over, check for fuel injector pulse at multiple cylinders as you may just have an issue with that specific circuit.
3) If there is no pulse on all cylinders, check to see if the fuel injector is getting power with the key on and cranking. If still no injector pulse, then the computer is not pulsing the injectors open for some reason and more testing will be needed.
4) Again, you want the Noid light to blink consistently when cranking the engine over. This is a good signal.
5) Some Noid light sets come with two different IAC motor circuit testers which are good to see this same type of signal from the computer to the Idle Air Control motor on a conventional throttle body set up.