6-14
Vehicle Testing Procedures
Exhaust Leak Test
The analyzer is extremely sensitive to HC, even at relatively low
concentrations. Therefore, it is useful for checking exhaust system
components for leaks. A leak in the exhaust system can lower the
HC, CO and CO
2
readings at the tail pipe, while raising the O
2
reading.
Testing Tips
Avoid touching the exhaust system with the probe.
Scaling particles from the exhaust system may
contaminate the sampling system and affect
analyzer accuracy.
X
Choke the carburetor intake slightly or partially block the tail
pipe with a socket having an outside diameter no larger than
1/2 the inside diameter of the tail pipe.
— Some exhaust systems have a small hole in the muffler to
allow moisture formed in the system to drain out. This does
not affect test results and exhaust leakage from this hole is
normal.
X
On pulse air systems, carefully check the fresh air side of the
check valve while the engine is running. An HC reading in this
area suggests a defective check valve, which can cause
vehicle performance problems since exhaust gases are being
fed into the intake air of the engine. If this occurs over a long
period, corrosion of the throttle body/carburetor can block air
bleeds and other vital orifices, causing increasingly poor
engine performance.
X
With the air injection system disabled, CO
2
readings less than
8% vol indicate that ambient air is entering the sample. Check
the integrity of the exhaust system and the exhaust sample
hose to see if ambient air is reaching the sample probe from
the tail pipe.
Test
1. With the engine running, move the probe along the
exhaust system and watch for any sudden increases in
HC.
2. Hold the probe near suspected surfaces of all exhaust
system components.
3. On vehicles with air pumps and pulse air systems, check
the components associated with these systems.
Interpretation
The HC reading increases in the area of an exhaust leak.
To Next Page
Loading...