Reference Material: Cracking open Injector Lines
From time to time, we ask all sorts of questions. Sometimes we may forget who's even asking... forgeting that once ourselves, did not know all these wonderful things about these engines.
So, that being said, let's get you clued in on what we mean by "cracking an injector line." If you look for the injectors, (see also picture thread in FAQ's) you'll see the silver line that comes from the injection pump down to the nut on the back of the injector. Loosen the nut on the back of the injector. This breaks the seal between the nut and injector and will allow the fuel to seep out around the nut. This is for diagnostic purposes only to prove that fuel is making it to the injector itself.
Won't the fuel come spraying out? No, it will just dribble most of the time. Injection pumps will deliver "small" doses of fuel to each injector under very high pressure. High pressure comes from resistance to flow, which the injector proves, by not opening until 1700 psi. So, with the nut on the back loosened, the fuel follows the path of least resistance, and comes out from around the nut, instead of the injector nozzle on the inside of the engine.
What does this prove? In cracking the injector line open, it proves you have fuel to that point in the fuel system. If you don't have fuel delivery that far, then you need to back track farther in the system to find out where fuel is, and is not.
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*Bus 1, rest in peace. Bone stock, now just bones. 4.10 rear 10/13 mpg, 182,000 miles with a set of MCI motor coach seats.
*Currently driving an "Canadian Camo" Snow White 2001 5.7L Chevy Express.
*Bus 2, 99 7.3L PSD.