Fuel Evaporation System Cadillac Brougham I

DESCRIPTION

Carbon canister storage is used for evaporative fuel control on all General Motors vehicles. The function of evaporative emission control system is to store gasoline fumes from fuel tank and carburetor in a carbon canister until fumes can be drawn into engine for burning during combustion process.

There are 4 basic components used in the evaporative emission system.

1. Activated carbon canister (may be sealed or open at top or bottom for fresh air intake).
2. Vacuum operated canister control valve (may be mounted on canister or remotely).
3. ECM-controlled solenoid (may be mounted on canister or remotely).
4. Tank pressure control valve (may be mounted internal or external of fuel tank).

The 5.0L (VIN Y) carbureted model uses a thermal bowl vent valve installed in the fuel bowl vent hose. For specific component application and vacuum hose routing, see VACUUM DIAGRAMS article.

Scheme 33

Scheme 34

CARBON CANISTER

Evaporative fumes from the fuel tank and fuel bowl (carbureted models) are vented through hose(s) into a canister containing activated carbon. The activated carbon absorbs and holds fuel vapors when the engine is not operating. When the engine is started and engine speed is greater than idle (purge at idle would cause too rich a mixture), engine vacuum draws fuel vapors from the canister into the engine. Regulation of vapors through this purge line may be controlled by a vacuum canister purge valve, an ECM-controlled solenoid, or both.

Carbon canisters are either open or closed in design. When the engine is started on open canister models, engine vacuum draws outside air into canister either through the top or through a filter in bottom of canister. (Scheme 35) This helps to purge vapors from the activated carbon.

Scheme 35

CANISTER CONTROL VALVE (CCV)

There are 2 types of vacuum operated canister control valves. In some applications, more than one type may be used on the same system.

The type 1 control valve is vacuum operated and is an integral part of the carbon canister (Y Body). When the engine is not running, vapor from the fuel tank is stored in the carbon canister. When the vehicle is started, vacuum to the upper port will draw in the internal vacuum diaphragm, opening the port between the canister and purge vacuum.

The type 2 control valve is similar to the type 1 valve, except it is located in the canister purge lines itself (5.0L VIN Y). When vacuum is applied to the upper port of valve, diaphragm is lifted, opening port between purge vacuum and accumulated vapors. When engine is off, valve diaphragm is closed by internal spring pressure, preventing vapor from venting to atmosphere.

PURGE SOLENOID VALVE

Purge solenoid valve is controlled by the Electronic Control Module (ECM). Current is supplied to solenoid when the ignition is on. Solenoid is energized when ECM provides a ground circuit for solenoid. When energized, purge solenoid valve opens, allowing purge. When de-energized, valve closes, blocking purge. The ECM will energize the canister purge solenoid when engine has been running for more than one minute, coolant temperature is above 176°F (80°C), vehicle speed is above 5 MPH and throttle is off idle. This solenoid is located in the purge line on W Body models, and on the canister on all other models.

FUEL TANK PRESSURE CONTROL VALVE

Note. Models without fuel tank pressure control valves may utilize a special pressure/vacuum relief fuel tank filler cap or other external relief device.

Fuel tank pressure control valve is a vacuum regulated/pressure control valve located in the fuel tank, or in the vapor delivery hose between fuel tank and carbon canister. When engine is not running and tank pressure is less than .9 psi (.06 kg/cm 2 ), internal spring pressure holds valve in the closed position. This causes fuel tank low-pressure vapors to be vented through a restriction in valve. This restriction will retain most of fuel tank vapors in fuel tank. When tank pressure rises and overrides spring tension, fumes are vented to the carbon canister. When engine is running, vacuum is applied to upper port of valve, opening passage between fuel tank and carbon canister, which is purged by engine vacuum.

THERMAL BOWL VENT VALVE (TBVV)

On carbureted models, the thermal bowl vent valve (located in the bowl vent hose) permits fuel bowl vapors to be directed to carbon canister for storage. When engine temperature is less than 90°F (32°C), valve will be in closed position, blocking bowl venting. Valve will open when engine temperature is greater than 120°F (49°C).

MAINTENANCE

Check all fuel and vapor lines for proper connections and correct routing. Remove canister and check for cracks or other damage. Replace damaged or deteriorated parts as necessary. Replace filter in bottom of canister if dirty or clogged (if equipped).

Perform a visual check of the carbon canister for the following

1. Filter at bottom of canister (if equipped). Replace if dirty or missing.
2. Cracks or external damage to canister body or tubes. Replace if necessary.
3. Fuel leakage from bottom of canister. Check entire system and hose routing.
4. Type 2 purge valve (if equipped).

Type 1

1. Note vacuum hose location and disconnect hoses from canister purge valve and canister. Install short length of hose to lower tube of carbon canister valve. Blow into hose. Air should not pass through canister. If it does, replace valve/canister.
2. Using a hand-held vacuum pump, apply 15 in. Hg to vacuum trigger port. With vacuum applied, again blow into hose installed on bowl vent tube. Air should now flow through canister. If it does not, replace valve/canister.

Type 2

1. Note vacuum hose location and remove valve from vehicle. Install a short length of hose to the vacuum trigger port. Blow into hose. Air should not pass through. If it does, diaphragm is ruptured and valve must be replaced.
2. Using a hand-held vacuum pump, apply 15 in. Hg to the vacuum trigger port . Vacuum should hold for 20 seconds. If it does not hold, replace valve.
3. With vacuum still applied to trigger port, blow through canister tube. Air should exit from vacuum purge tube. If it does not, replace valve.

Scheme 36

PURGE SOLENOID VALVE CHECK

For testing of solenoid control portion of fuel evaporation system, see appropriate C-3 chart in the COMPUTERIZED ENGINE CONTROLS section.

1. Remove valve from vehicle. Using a hand-held vacuum pump, apply 15 in. Hg to the upper trigger port. Vacuum should hold for 20 seconds. If it does not hold, replace valve.
2. Install a short length of hose to the valve tank vent tube. Lightly blow into hose. Valve should pop open and air should pass through valve. If the valve does not pop open, replace valve.

1. On carbureted models, remove valve from vehicle. Allow valve to cool to less than 90°F (32°C). Install a short length of hose to either valve port. Lightly blow into hose. No air should pass through valve. If it does, replace valve.
2. Warm valve to greater than 120°F (49°C). Once again, blow into hose. Air should now pass through valve. If it does not, replace thermal bowl vent valve.