GM Storm/Spectrum 1985-1993 Repair Guide

Fuel Evaporative Emission Control System

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OPERATION



See Figures 1 through 6

The Evaporative Emission Control System (EECS or EVAP) limits the amount of fuel vapors that are allowed to escape into the air. When the engine is not running, fuel vapors from the sealed fuel tank flow through the single vapor line to the charcoal canister which is normally mounted in the engine compartment. The charcoal absorbs the fuel vapors and retains them until they are purged with fresh air.

Once the engine is started and the appropriate operating conditions are reached, the Engine Control Module (ECM) will operate a solenoid valve in order to provide vacuum to the canister purge valve. The vacuum will open the normally closed purge valve against diaphragm spring pressure. With the purge valve open, intake manifold vacuum is applied to the canister drawing in fresh air and purging the vapors. The purged vapors are then drawn into the engine and burned efficiently during the normal combustion process.

On carbureted vehicles, a Thermal Vacuum Valve (TVV) is connected in series to the purge signal line. The TVV prevents vapor purge during engine warm up under cold driving conditions in order to assure the proper air/fuel ratio.

For fuel injected vehicles, the ECM uses feedback from the engine coolant temperature and other sensors to determine purge valve activation. The ECM will prevent vapor purge when the engine is cold and while under idle conditions. For these engines, the ECM will wait until a specified coolant temperature is reached and for the engine to run continually for a predetermined amount of time before activating the purge valve.



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Fig. Fig. 1: Evaporative emission control system schematic - Spectrum



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Fig. Fig. 2: Evaporative emission control system schematic - Storm 1.6L engines



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Fig. Fig. 3: Evaporative emission control system schematic - Storm 1.8L engine



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Fig. Fig. 4: Canister and system operation - Spectrum (Storm systems similar)



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Fig. Fig. 5: Cut-away view of the canister assembly - 1.6L Storm engines



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Fig. Fig. 6: Cut-away view of the canister assembly - 1.8L Storm engine

SERVICE



See Figures 7 and 8

Carefully check for cracks or leaks in the vacuum lines or in the canister itself. The lines and fittings can usually be reached without removing the canister. Cracks or leaks in the system may cause poor idle, stalling, poor driveability, fuel loss or a fuel vapor odor.

Vapor odor and fuel loss may also be caused by; fuel leaking from the lines, tank or injectors, loose, disconnected or kinked lines or an improperly seated air cleaner and gasket.

If the system passes the visual inspection and a problem is still suspected:

  1. For Carbureted vehicles:
    1. Locate the tank pressure control valve (inline between the fuel tank and canister) and disconnect the rubber hoses.
    2.  
    3. Use a hand vacuum pump to apply 7.5-8.5 kPa of vacuum to hose A (valve vacuum fitting). If the valve is operating properly, it should open.
    4.  
    5. Apply 7.5-8.5 kPa of vacuum to hose B while capping hose C with your finger or a rubber plug. Air should not pass through the valve.
    6.  
    7. If the tank pressure valve is good, check the purge valve located on top of the canister. Apply 50 kPa of pressure to port marked V.C. and check for air leakage. Air should not leak from the diaphragm.
    8.  
    9. Apply 380mm Hg (14.96 in. Hg) of vacuum to the port marked PURGE and maintain vacuum. Using a second pump, gradually apply vacuum to the port marked V.C. while watching the first vacuum gauge. If the reading on the PURGE vacuum port decreases as the 2nd gauge approaches 40-80mm Hg (1.6-3.2 in. Hg), then the purge valve is operating normally.
    10.  
    11. Replace any component which fails to operate sufficiently.
    12.  

  2.  
  3. For the Storm 1.6L engines:
    1. Connect a length of reasonably clean hose (at least at your end) to the lower tube of the purge valve and attempt to blow through it. Little or no air should pass through the canister. Some vehicles utilize a canister with a constant purge orifice which will allow a minimal amount of air to pass even with the purge diaphragm closed.
    2.  
    3. Use a hand vacuum pump to apply 51 kPa (15 in. Hg) to the control valve (canister upper tube). If the diaphragm hold the vacuum, attempt to blow through the hose (still connected to the lower tube) again. With the vacuum applied, an increased flow of air should be blown through the tube.
    4.  
    5. If the valve does not operate properly, then canister/valve assembly must be replaced as a unit.
    6.  

  4.  
  5. For the Storm 1.8L engine, refer to the diagnostic charts at the end of this section.
  6.  



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Fig. Fig. 7: Testing the tank pressure control valve - Spectrum



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Fig. Fig. 8: Testing the canister purge control valve - Spectrum

REMOVAL & INSTALLATION



Charcoal Canister
  1. Disconnect the negative battery cable if any tools might come in contact with electrical connections, wires or switches.
  2.  
  3. Tag and disconnect the vacuum hoses from the canister.
  4.  
  5. Remove the canister or canister bracket fastener, then remove the charcoal canister assembly from the vehicle.
  6.  
  7. Installation is the reverse of the removal procedure. Be sure to fully seat, but not overtighten the canister and/or bracket retainers. The vacuum hoses MUST be properly installed for the system to operate correctly.
  8.  

 
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