HF10 - Check Vacuum For Indication of Exhaust Restriction

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

- Vacuum gauge installed.

- Tachometer installed.

- Key On, Engine Idling.

- Increase the engine speed gradually from base idle rpm to 2000 rpm with the transmission in NEUTRAL.

- Observe the speed the vacuum gauge needle rises. while maintaining the increased engine rpm.

NOTE 1:
On a non-restricted exhaust system, the vacuum gauge needle will rise quickly to the normal range as the increased rpm is maintained.

NOTE 2:
On a restricted exhaust system, the vacuum gauge needle will rise slowly to the normal range as the increased rpm is maintained.

NOTE 3:
The rate of speed the vacuum gauge needle rises to the normal range is slower on a restricted system than on a non-restricted system as the increased rpm is maintained.

- Decrease engine speed to base idle rpm.

- Key Off.

- Is the rate of speed that the vacuum gauge needle rises back to the normal range (above 16 inches Hg) much slower than that of a non-restricted system?

YES -- A moderate restriction may be present. GO to HF11. HF11 - Check Manifold Vacuum With Exhaust Manifold Disconnected

NO -- No indications of restrictions or leaks have been detected in the exhaust system. If here because of DTC 0420 or 0430, the catalytic converter is chemically inactive. REPLACE the catalytic converter. COMPLETE the PCM reset to clear all DTCs. Clearing Diagnostic Trouble Codes

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

REMOVE the vacuum gauge and tachometer. For further diagnosis of symptom (e.g. Lack of Power, Loss of Power, or No Start) REFER to Symptom Flow Charts. Testing and Inspection