HF11 - Check Manifold Vacuum With Exhaust Manifold Disconnected

*** THIS ARTICLE REFLECTS CHANGES MADE BY TSB # 9326B7, December 1993

- Key Off.

- Disconnect exhaust system immediately after the exhaust manifold.

- Repeat the vacuum measurement found in test step HF10.

- Did the vacuum needle quickly rise above 16 inHg with the engine rpm at 2000?

NOTE: An intake manifold gasket leak can also cause the vacuum gauge needle to remain well below the normal range.

YES -- The exhaust system restriction is downstream of the exhaust manifold. RECONNECT exhaust system at exhaust manifold. GO to HF12. HF12 - Check Vacuum Without Muffler/Tailpipe

NO -- A restriction is present in the exhaust manifold. REMOVE the vacuum gauge and tachometer INSPECT each exhaust port for casting flash/restrictions by dropping a length of chain into it (NOTE: Do not use a wire or lamp to check the ports. The restriction may be large enough for either to pass through, but small enough to cause excessive back pressure at high engine rpm.). REPLACE the exhaust manifold if unable to remove the casting flash/restriction. COMPLETE the PCM reset to clear all DTCs. Clearing Diagnostic Trouble Codes

Rerun quick test. Diagnostic Subroutines (DSR) - Extracting Codes