Snap-On Diagnostics DGA 1000, Manual, Page: 105 / 116

Vehicle Testing Procedures
6-11
4. While holding the fast idle cam with one hand, quickly open
and return the throttle to the same fast idle position.
It is possible for the engine to backfire during this
test. Never position yourself in a way that could
expose you to the heat/flame of an intake system
backfire.
✓
It is important to always return to the same fast idle cam
position to check for proper re-seating of the power
valve.
5. Observe the CO reading.
Interpretation
• The CO reading should increase a minimum of 1% vol when the
engine is accelerated.
• If the CO does not increase, a malfunctioning power valve is
indicated.
• A momentary increase in, and return to, the original CO and HC
readings is expected when the throttle is opened and returned to
fast idle position.
High Fuel Level In Float Chamber Test
If the float level is set too high or the float is heavy due to absorbed
fuel, the engine may:
•
Have a rough idle,
•
Be difficult to restart when hot, and
•
Have a high CO reading at idle.
✓
Floats made of nytrophyl are more prone to this
condition.
Test
1. Bounce the vehicle several times with the engine running.
2. Note the CO reading.
Interpretation
•
A fluctuating CO reading indicates a high fuel level in the float
chamber.
— Verify that the float level setting and float weight meet
manufacturer specifications.