Using Manifold Vacuum Port

NOTE: A partially restricted or blocked exhaust system usually results in a loss of power or backfire up through the throttle body. Verify that the condition is not caused by ignition, compression or fuel system problems, then perform a visual inspection of the exhaust system. If the condition cannot be located by visual inspection, perform the easiest of the following procedures.



DIAGNOSIS AT MANIFOLD VACUUM PORT

1. With engine at normal operating temperature, connect a vacuum gauge to any convenient manifold vacuum source.
2. Run engine at 1000 rpm and record vacuum reading.
3. Increase rpm slowly to 2500 rpm, and note vacuum reading at a steady 2500 rpm.
4. If vacuum at 2500 rpm decreases more than 3" Hg, from reading at 1000 rpm, the exhaust system should be inspected for restrictions.
5. Disconnect exhaust pipe from engine and repeat Step 3 & 4. If vacuum still drops more than 3" Hg, with exhaust disconnected, check for exhaust manifold restriction.