HF9 - Check Vacuum For Indication of Exhaust Restriction

- Attach a vacuum gauge to the intake manifold vacuum source.

- Install a tachometer.

- Observe the vacuum gauge needle while performing the following:
- Start the engine and gradually increase the rpm to 2000 with the transmission in NEUTRAL.

NOTE: The vacuum gauge reading may be normal when the engine is first started and idled. However, excessive restriction In the exhaust system will cause the vacuum gauge needle to drop to a low point even while the engine is idled.

- Decrease engine speed to base idle rpm.

- Key Off.

- Did manifold vacuum rise above 16 Inches Hg with the engine rpm at 2000?

YES -- GO to HF10. HF10 - Check Vacuum For Indication of Exhaust Restriction

NO -- Manifold vacuum did not reach an acceptable level. An excessive restriction may be present. GO to HF11. HF11 - Check Manifold Vacuum With Exhaust Manifold Disconnected