Component Tests and General Diagnostics

EXHAUST SYSTEM CONNECTED

NOTE: A blocked or restricted exhaust system usually results in loss of power or popping through the intake. Before proceeding with diagnosis, verify that condition is not caused by ignition or timing problems.

1. Visually inspect exhaust system for collapsed pipes, holes and cracks.
Replace any damaged components.
2. Attach vacuum gauge to intake manifold vacuum source.
3. Connect tachometer.
4. Start engine and observe vacuum gauge needle.
5. Gradually increase engine speed to 2000 rpm.

NOTE: Vacuum gauge reading may be normal when engine is first started and idled. However, excessive exhaust system restriction will cause vacuum reading to drop off while engine is idling.

6. Did manifold vacuum reach above 16 inches?
If so, there is no restriction within the exhaust system. Decrease rpm to idle speed.
If not, proceed to next step.
7. With vacuum gauge and tachometer still in place, increase engine speed to 2000 rpm.
8. While maintaining increased engine rpm, observe RATE at which vacuum gauge reading falls and rises:
a. On a non-restricted system, gauge will drop to zero and then return to normal reading without delay.
b. As engine speed is raised to 2000 rpm on a restricted system, gauge will slowly drop to zero and slowly rise to normal.
c. Rate at which gauge reading returns to normal is much slower on a restricted system than on a non-restricted system.
9. Decrease engine rpm to base idle.
10. Was gauge return rate much slower than on a non-restricted system?
If not, there is no exhaust system restriction.
If so, proceed to next section.

EXHAUST SYSTEM DISCONNECTED

1. Turn engine "OFF."
2. Disconnect exhaust system at muffler.
3. Repeat vacuum test.
4. Did manifold vacuum reach above 16"? If so, replace muffler. If not, proceed to next step.
5. Turn engine "OFF."
6. Disconnect exhaust system at catalytic converter.
7. Repeat vacuum test.
8. Did manifold vacuum reach above 16"? If so, replace converter. If not, proceed to next step.
9. Turn engine "OFF."
10. Disconnect exhaust system at exhaust manifold.
11. Repeat vacuum test.
12. Did manifold vacuum reach above 16". If so, restriction is located between exhaust manifold and catalytic converter. If not, proceed to next step.
13. Remove the exhaust manifold and inspect ports for casting flash by dropping a length of chain into each port.

NOTE: Do not use a wire or a lamp to check ports. Restriction may be large enough for wire or light to pass through but small enough to cause excessive back pressure at high rpm.

14. Is a restriction present? If so, remove casting flash or replace exhaust manifold.