Dodge Omni/Horizon/Rampage 1978-1989 Repair Guide

Evaporative Emission Controls

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OPERATION



The function of the evaporative control system is to prevent the emissions of gasoline vapors from the fuel tank into the atmosphere. When the fuel evaporates in the fuel tank, the vapors pass through a vent hoses or tubes to a charcoal canister where they are temporarily held until they can be drawn into the intake manifold when the engine is running. This system is called bi-level purge system where there is a dual source of vacuum to remove fuel vapor from the canister.



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Fig. Fig. 1 Schematic of a common evaporative emission control system

On fuel injected and turbocharged engines, the source of vacuum at idle is a tee in the PCV system.

The Evaporation Control System should not require service other than replacement of the charcoal canister filter or possibly the rollover valve. All hoses should be inspected and replaced if cracked or leaking. Any loss of fuel or vapor from the filler cap would indicate one of the following conditions:



Poor seal between cap and filler neck
 
Malfunction of fuel cap release valve
 
Plugged vent line roll-over valve in the fuel tank
 
Plugged vapor vent lines between fuel tank and charcoal canister
 

All 1978-89 models pass a full 360° rollover without fuel leakage. To accomplish this, fuel and vapor flow controls are required for all fuel tank connections. A rollover valve is mounted in the top of the fuel tank to prevent leakage if a vehicle is accidentally rolled over.

A purge solenoid is used and is controlled by the engine control module. During warm-up and for a specified time period after hot starts, the engine control module grounds the solenoid causing it to energize. This prevents the vacuum from reaching the charcoal canister valve. When the engine reaches a specified operating temperature and the time delay interval has occurred, the solenoid is de-energized by turning off the ground. Once this has occurred, vacuum will flow to the canister purge valve and purge fuel vapors through the throttle body. The solenoid will also be energized during certain idle conditions, this is to update the fuel delivery calibration.

SERVICING





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Fig. Fig. 2 The charcoal canister is mounted in the engine compartment

The only service is to replace the canister filter every 30,000 miles (50,700 km), if the car is driven in particularly dusty areas. Otherwise, no service is necessary.



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Fig. Fig. 3 The filter is located on the bottom of the canister

All hoses used with this system should be inspected periodically and replaced if cracked or leaking. These hoses are of special fuel resistant material and must be replaced with the same type and quality. The OEM (Original Equipment Manufactured) clamps are Keystone type and will be destroyed when they are removed. Replacement types should be aircraft type screw clamps if the original equipment is not available (spring type clamps are not recommended). Position the clamps so that no sharp edges contact adjacent hoses.

REMOVAL & INSTALLATION



Rollover Valve
  1. Remove the fuel tank.
  2.  
  3. Wedge the blade of a screwdriver or suitable prytool between the rubber grommet and the support rib on the fuel tank.
  4.  



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Fig. Fig. 4 Use a large screwdriver as a fulcrum to pry the valve from the tank



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Fig. Fig. 5 To install the valve, simply push it back into place

  1. Use a large screwdriver as a fulcrum and pry the valve and grommet from the tank.
  2.  


WARNING
Do not pry between the valve and grommet.

  1. To remove the grommet from the valve, place the valve upright on a flat surface and push down on the grommet.
  2.  

To install:

  1. Install the rubber grommet in the fuel tank and work it around the curled lip.
  2.  
  3. Lubricate the grommet with engine oil and twist the valve down into the grommet.
  4.  
  5. Install the fuel tank.
  6.  

Canister Purge Solenoid
  1. Unplug the hoses and electrical connection from the solenoid.
  2.  
  3. Remove the retainers securing the solenoid, then remove the solenoid from the vehicle.
  4.  
  5. Installation is the reverse of removal.
  6.  

Charcoal Canister
  1. Label and disconnect the hoses from the canister.
  2.  
  3. Remove the retainers securing the canister, then remove the canister from the vehicle.
  4.  
  5. Installation is the reverse of removal.
  6.  

 
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