Range Rover (LM) V8-4.4L (2009)
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Evaporative Emissions Hose: Description and Operation
PURGE VALVE AND HOSES
The purge valve is located at the rear of the engine on the left hand side, on a bracket which is attached to the left hand cylinder head. The purge hose is
routed from the purge valve, into the induction elbow and is secured with a quick fit connector.
The purge hose is routed from the purge valve, along the top of the left hand rocker cover to a quick release coupling. From the coupling, the hose is
routed down the left hand side of the engine compartment to the purge line which runs parallel with the fuel feed line along underside of the vehicle and
across the top of the fuel tank to the charcoal canister.
The purge valve is a solenoid operated valve which is closed when de-energized. The valve is controlled by the Engine Control Module (ECM) and is
operated when engine operating conditions are correct to allow purging of the charcoal canister.
The purge valve is Pulse Width Modulated (PWM) at 10Hz by the ECM. At this high frequency, the pulses of purge gas flow into the induction elbow in
an almost a continuous flow. The valve operates between 7% and 100% duty or mark space ratio (% open time).
The atmospheric pressure at the air intake vent of the system is higher than the inlet manifold pressure under all throttled engine running conditions. It is
this pressure differential across the system that causes the air to flow through the air intake, through the purge system, and in to the engine. The operation
of the supercharger does not affect the purging process.
The ECM waits until the engine is running above 40°C (104°F) coolant temperature with closed loop fuel operational before the purging process is
activated. Under these conditions the engine should be running smoothly with no warm up enrichment. The purge valve duty (and flow) is initially
ramped slowly because the vapor concentration is unknown (a sudden increase in purge could cause the engine to flood). The concentration is then
determined from the amount of adjustment that the closed loop fueling is required to make to achieve the target Air Fuel Ratio (AFR). Once the
concentration has been determined, the purge flow can be increased rapidly and the injected fuel can be proactively adjusted to compensate for the
known purge vapor and the target AFR control is maintained.
When the purging process is active, fresh air is drawn into the charcoal canister via the DMTL valve atmospheric vent connection and its filter on NAS
vehicles or, via the vent hose connection and the spider trap on non NAS vehicles.
On NAS vehicles the system does not include a pressure test point. Pressure testing of the purge valve hose is achieved by disconnecting the purge valve
joint above the left hand engine rocker cover and connecting a special tool to allow the system to be pressure tested. The test performs a pressure test on
the purge hose connection back to the charcoal canister. The special tool is then connected to the purge hose connection to the purge valve to perform a
pressure test on the purge hose to the purge valve.
