The other day I was removing my plenum for some cleaning. After I got the plenum off I was standing on the passenger side of the car and I heard a strange high pitched hissing sound. Like something was leaking somewhere. I used a 5/8" heater hose and located the source where the sound seem to come from. It was the last runner tube on the driver's side. Which of course goes to the #8 cylinder. So I put the heater hose inside the runner just to be sure and the noise got louder. The only thing I could think that would make this noise is a leaking fuel injector or the head gasket since the engine wasn't running but the fuel system still had a little bit of pressure and the cooling system was still pressurized a little. But about a month ago I rented a pressure tester and determined that the head gaskets are sealing fine and the cooling system bled off minimal pressure and was in spec with what the booklet said. Does this sound like a leaky injector? Would it make a hissing sound if it was leaking? Any other suggestions as to what it could have been? I don't really have any driveability problems. Just wondering what was leaking.

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1991 5.7L Z28 - gutted air boxes, K&Ns, airfoil, ported plenum, relocated MAT, accel TPI base, accel 300+ ignition, accel cap&rotor, homemade AFPR, derale fan switch, vette servo ,flowmaster exhaust, torque conv. lock-up switch, and fresh 255/50/16 Dunlop sp800s. More to come!

 

bleed off fuel pressure from the system by means of the scrader valve on the fuel rail (looks like a tire valve stem, but slightly larger) just use a screwdriver as if you were letting air out of a tire, being careful since the fuel will spray, see if the hissing stops with no pressure remaining in the system..

 

You could buy a fuel pressure gauge for like $15 and see if pressure is leaking down. just something that could come in handy