BMW Coupes and Sedans 1970-1988 Repair Guide

Evaporative Emissions Control System

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See Figures 1, 2, 3 and 4



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Fig. Fig. 1: Typical evaporative emissions control system-4-cylinder engine



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Fig. Fig. 2: Typical evaporative emissions control system-6-cylinder engine



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Fig. Fig. 3: Evaporative emissions control system-528e model



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Fig. Fig. 4: Common 533i, 633i and 733i evaporative emissions control system

OPERATION



See Figure 5

This system stores gasoline vapors which collect above liquid fuel in the fuel tank and, on carbureted engines, in the float bowl. The system stores the vapors while the engine is off, and then allows the vacuum created in the intake manifold to draw them off and burn them when the engine is started.



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Fig. Fig. 5: Carbon canister in 2002 engine compartment

Fuel tank vapors are collected by a storage tank located in the trunk. Vapor which cannot be held there, as well as float bowl vapors, are stored in a charcoal canister located in the front of the engine compartment. The charcoal has the effect of keeping the vapors in liquid form so they can be held in a minimal space. As in the case of the crankcase ventilation system, no fresh air is used in purging, eliminating the need to change an air filter in the canister.

MAINTENANCE



Inspect the hoses and hose clamps occasionally or if raw fuel odor is noticed. Tighten clamps as necessary or replace hoses which have cracked.

Under certain operating conditions, contamination or excessive vapor collection may cause the vapor canister to become saturated with liquid fuel. Under these conditions, the unit should be replaced, even though replacement on a routine basis is not necessary.

 
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