And correct the applicable causes if necessary

CO

HC

Problems

Causes

Normal

High

• Incorrect timing

• Fouled, shorted or improperly gapped plugs

• Open or crossed high-tension cords

2. Incorrect valve clearance

3. Leaky intake and exhaust valves

4. Leaky cylinders

Low

(Fluctuating HC reading)

1. Vacuum leaks:

• Intake manifold

• Throttle body

2. Lean mixture causing misfire

High

(Black smoke from exhaust)

1. Restricted air filter

2. Plugged PCV valve

3. Faulty EFI systems:

• Faulty pressure regulator

• Defective water temperature sensor

• Defective air flow meter

• Faulty injectors

• Faulty throttle position sensor

Normal

High

• Faulty actuator

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