By-Pass Valve Test

Set transmission in neutral or "P", apply parking brake and warm engine to normal operating temperature. Stop engine and remove air by-pass valve-to-manifold check valve hose at by-pass valve. On models which have "T" fitting, remove both hoses connecting by-pass valve to check valves. Install tachometer to engine.
Start engine and accelerate to 1500 RPM. Check that air flows from by-pass valve hose connections (feel with hand).
Remove vacuum hose from by-pass valve and plug hose. With engine still running at 1500 RPM, no air flow should be coming from by-pass valve connection (air flow will be discharged silently through exhaust ports in end of valve silencer cover). If valve does not respond as indicated, replace by-pass valve.
Stop engine. Remove plug from vacuum hose. Reinstall vacuum hose on by-pass valve vacuum sensing nipple. Install pressure gauge tool (T75L-9486-A or equivalent) to by-pass valve outlet, using short piece of hose. If by-pass valve has two outlets, plug one without gauge. If valve has small sensing nipple as one outlet, install gauge on this outlet.
Start engine and run at 1000 RPM. Observe pressure produced at test gauge. It should be 2.25 psi (15.8 kg/cm² ). If not, replace valve.