When cranking that would be normal.
Computer uses Batch fire during startup.
On a 4.0l computer would open 3 injectors each time an intake valve is opening, then opens the other 3 on the next intake valve opening.
So on a cranking engine this would appear as all 6 "firing" at the same time.
Once engine starts the Cam Position Sensor(CPS) will take over the injectors and switch to Sequential injection, so each cylinder's injector only opens during its intake stroke.
There are Noid Lights that can be used to test when injectors are opened, or grounded, computer grounds an injector to open it.
If CPS fails for any reason the computer switches over to Batch fire so engine will still run fine, it just uses slightly more fuel.
Batch fire was the standard on early mass production fuel injection.