Fuel Delivery and EVAP Basics
Pumps, filters, pressure and the evaporative emission system.
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What you will learn
- Describe the fuel path
- Explain fuel pressure and volume
- Explain the EVAP system
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Fuel travels from the tank through a filter to the engine, where it is delivered at controlled pressure. Pressure alone is not enough: the system must also flow enough volume under load, and a weak pump can show good pressure at idle yet starve the engine at speed.
The evaporative emission (EVAP) system captures fuel vapour from the tank and burns it through a purge valve rather than releasing it. EVAP leaks are among the most common emissions faults, and a loose fuel cap is a classic cause.
| Check | What it proves |
|---|---|
| Fuel pressure | Delivery pressure at the rail |
| Fuel volume | Flow under load |
| Filter condition | Restriction |
| EVAP leak test | Vapour system sealing |
Key points
- Pressure and volume are different tests.
- A restricted filter reduces both.
- A loose fuel cap is a common EVAP fault.
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Key points
- Pressure and volume are both required
- The filter protects the system
- EVAP captures fuel vapour
All values shown are training examples. Real thresholds depend on the manufacturer, engine, temperature and system — always confirm with the vehicle service documentation.
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