Originally Posted by 1993 SLE
coming along Very nicely Curt
Thanks, another day, another little mini-project.
No dice on the coolant elbows and water-neck, so I figured I could test a few of the sub-systems to see that everthing was working as it should prior to being installed in the car.
This little "Rube Goldberg" contraption is how I test the injector rails and the injectors themselves. In the photo, the gauges are regular R-12 A/C manifold gauges. Since I converted the rail to run with AN-4 fittings on the outlet side, no adaptors were needed to hook these up. The red hose (High Pressure gauge) is connected to the schraeder valve on the opposite side of the motor. The blue hose (Low Pressure gauge) is connected to the fuel return line. The black hose is from the air compressor in the garage and is connected via a coupling (quick disconnect barb to 3/8 NPT, then to a 3/8 NPT to AN-6 fitting) to the AN-6 fitting I installed on inlet side of the rail. The little hand pump is connected to the vac fitting on the fuel pressure regulator.
If your rails are regular GM quick disconnects, you can do the same thing but you will need to buy or make converters (using a junkyard pair of GM fuel lines and hose barbs)
With the rail pressurized, I'm listening for any hissing air that would indicate a stuck injector or an O-ring failure. As you bring the air pressure up, you low side gauge will suddenly jump from 0 to the high side pressure. That'* the point where the regulator is opening to dump the excess pressure overboard. Try it a couple of time with various amounts of vac and pressure on the regulator fitting and you can map out actual fuel rail pressure the regulator will set vs. the amount of boost or vac signal comming from the manifold. (Crack open the low side of the A/C Manifold gauges so the output of the regulator has some place to go...it can only dump the excess pressure to the return line, so you have to open the return line and allow the pressure drop to occur)
For reference sake, I plotted the rail pressure vs. the signal vac. With zero signal pressure, the regulator opens at 54 psi rail pressure. With 20 inches of vac on the regulator signal, the regulator opens at 50 psi rail pressure. The regulator is linear, with about a 1 psi drop in rail pressure for every 5 inches of vac. I ran out of pressure gauges, so I can't measure the rail pressure vs. positive boost pressure on the regulator, but I would venture a guess that it will also be linear.
With a battery, pushbutton, and an old chunk of injector wiring harness, I can go down the line and pulse each injector, listening for an audible hiss of air when the injector open.
With this rig, you can also clean out the injectors off the car. Fill the rail and injectors up with carb cleaner. Let it sit for a little while to give the cleaner a chance to dissolve the varnish inside, then hook up the air pressure and start pulsing the injectors. If you do it on the work bench, you can stick the end of the injector in a can to catch the cleaner comming out when you pulse the injector. You can also see the spray pattern from the injector. Not really great for checking the actual flow rates, but good enough to know the injectors are going to work and you aren't going to be dumping fuel all over the place as soon as the pump kicks in.