As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING ENGINE STARTS, PNEUMATIC GAUGE SHOWED 2 BUTTONS WITH RIGHT ENGINE OFF AND ZERO PRESSURE. BOTH BUTTONS PULLED WHEN RIGHT ENGINE STARTED AND GAUGE INDICATED 5.25 INCHES. TROUBLESHOOTING REVEALED CHECK VALVES IN MANIFOLD LEAKING. VALVE HAD BEEEN INSTALLED NEW 11-21-95.