How do you check the injector spray pattern in '99 4.3? How do you get the injector to fire (squirt) to test the pattern? Just crank with the coil wire removed to prevent starting?

 

i believe that you can just apply voltage to the fuel injector with the pump on and it will work, not sure on how much voltage tho, ive heard 9v but not sure.

i would imagine that cranking will work as well.

 

First, you must remove the upper intake plenum from the motor. In that process, you will have to remove the fuel lines on top of the motor as well as disconnect the main engine harness from the engine compartment fuse box. Once the upper plenum is off, you must reconnect the fuel lines to the feed & return lines at the back of the motor as well as into the SCFI spider. From there, you can either apply voltage directly to the injector as Zygoat has suggested (if you have any reservations about this, do not attempt it) or you will need to have a Tech2 or equivalent scan tool that has the injector test option. You will have to pull each of the poppet nozzles out of their bores in the lower intake and have them positioned over a container of some kind to keep from spraying fuel all over the place.

When I checked my injectors, I used my scan tool to cycle the injectors while I watched the pressure drop on my fuel pressure gauge as well as watched the spray pattern of each injector. I found that I had a slight pressure drop while all injectors were closed and found that 3 of my injectors were weeping pressure by. And only 2 injectors had decent atomization of the fuel during the actual injector test.