Troubleshooting

HC

CO

Symptoms

Causes

H»gh

Normal

• Incorrect timing

• Fouled, shorted or improperly gapped plugs

• Open or crossed ignition wires

• Cracked distributor cap

2. Faulty EGR system

3. Leaky exhaust valves

4. Leaky cylinder

High

Low

Rough idle Fluctuating HC reading

1. Vacuum leak:

• Intake manifold

2. Lean mixture causing misfire

High

High

Rough idle Black smoke from exhaust

1. Restricted air filter

2. Faulty EFI system:

• Faulty pressure regulator

• Clogged fuel return line

• Faulty air flow meter

• Defective water temp, sensor

• Defective air temp, sensor

• Faulty miector

• Faulty cold start injector

• Faulty throttle position sensor

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