CIS injector pressure?

[slater]

I thought I could find this info, but I did a search and came up with no results. What kind of pressure is it supposed to take to open up CIS injectors (off a 75 2.7s)? I thought it was quite high, but then I tried cleaning mine with some spray carb cleaner last night and was suprised by how easy I could spray through them. My can had a red WD-40 type straw on it, and if I hold the straw as tightly as possible in the end, I can get it to come out atomized on the other side. It was an excellent way to test if the spray pattern was right (sprayed onto a blank surface to see if it came out in an even pattern). kris out

[RoninLB]

'76-'77 Tech Spec handbook

[slater]

I guess I don't know enough about this.. but if that is how much pressure the system has, any idea how cloes a pressurized spray can would have? I am just trying to figure out if the spray can should be able to spray through like that. Anybody?

[sammyg2]

I have no idea how much pressure is in an aerosol can, but your injectors should not open or leak at any pressure lower than 40 psi. I don't have my book in front of me but I'll check for an exact pressure tomorrow.

[ChrisBennet]

I check CIS injectors using a can of Brake Kleen just like you did. I don't know if the can produce 40psi or if the injectors open with less pressure than you'd think.
-Chris

[sammyg2]

CIS systems are designed to hold residual fuel pressure to the injectors after the engine is shut off. This is to prevent vapor lock in the fuel lines above the engine.
the injectors have spring loaded valves in them that are supposed to close and hold pressure at somewhere just above 40 psi, I'll have to look up the exact pressure in my book at work.

When the fuel pump is shut off the pressure in the system drops until the point where the springs in the injectors close the valves and the injectors stop flowing. The pressure stays there for a while if everything is working right. Actually the pressure rises slightly as the fuel in the lines expands, but it supposed to stay at a high enough pressure to keep the fuel in the lines and injectors from boiling.
The pressure accumulator acts as a spring loaded bladder and allows the fuel to expand and contract while maintaining a steady pressure.
the pressure will drop over time but it is supposed to hold long enough for the fuel to cool down.
If the accumulator, fuel pump check valve or injectors leak, the pressure will drop too fast. The fuel will boil and cause vapor lock, or what is commonly called the CIS hot start problem.

If you don't have a hot start problem that means your system pressure is being maintained high enough and ong enough to prevent vapor lock and your injectors are holding.

[sammyg2]

My CIS book says that the injectors are designed to open at any pressure over 3.5 bar ( 51.45 psi). Anything under that pressure they should be completely closed and not leak.