What the hell does the EVAP canister do?
08-22-2001, 06:41 PM
#1
What does the EVAP canister do?
I am getting two trouble codes, both pointing to the same problem. 0705 and 0309....
0705 = EVAP control system leak?
0309 = EVAP canister vent control valve open
How does this EVAP canister work, does it clean the gasoline of foreign substances or what? I understand it involved emissions..
Also, I wanted to know if these things can lead to poor gas milage? I think the ghost of poor fuel economy hunts me, I will get only around 270 miles on this tank of gas... It's either that or I am a REALLY aggressive driver, although I never get bad gas milage on other cars.
Can anyone help me out? I am not quite sure that I understand what the sticky at the top states. I want to know if it can cause poor fuel economy as well...
thanks.
Steve
0705 = EVAP control system leak?
0309 = EVAP canister vent control valve open
How does this EVAP canister work, does it clean the gasoline of foreign substances or what? I understand it involved emissions..
Also, I wanted to know if these things can lead to poor gas milage? I think the ghost of poor fuel economy hunts me, I will get only around 270 miles on this tank of gas... It's either that or I am a REALLY aggressive driver, although I never get bad gas milage on other cars.
Can anyone help me out? I am not quite sure that I understand what the sticky at the top states. I want to know if it can cause poor fuel economy as well...
thanks.
Steve
08-22-2001, 07:04 PM
#2
Senior Member
Join Date: Jan 2001
Posts: 400
From Haynes:
The Evaporative Emissions Control (EVAP) system absorbs fuel vapors and, during engine operation, releases them into the engine intake where they mix with the incoming air-fuel mixture. The EVAP system consists of a charcoal-filled canister and the lines connecting the canister to the fuel tank, ported vacuum and intake manifold vacuum.
When the engine is not operating fuel vapors are transferred from the fuel tank, throttle body and intake manifold to the charcoal canister where they are stored. When the engine is running, the fuel vapors are purged from the canister by the purge control valve. The gasses are consumed in the normal combustion process.
Do you sometimes smell fuel fumes when you are running your engine? That might be due to a cracked canister or compromised fuel line or vapor hoses. This would explain both your lowered fuel economy as well as your trouble codes.
The Evaporative Emissions Control (EVAP) system absorbs fuel vapors and, during engine operation, releases them into the engine intake where they mix with the incoming air-fuel mixture. The EVAP system consists of a charcoal-filled canister and the lines connecting the canister to the fuel tank, ported vacuum and intake manifold vacuum.
When the engine is not operating fuel vapors are transferred from the fuel tank, throttle body and intake manifold to the charcoal canister where they are stored. When the engine is running, the fuel vapors are purged from the canister by the purge control valve. The gasses are consumed in the normal combustion process.
Do you sometimes smell fuel fumes when you are running your engine? That might be due to a cracked canister or compromised fuel line or vapor hoses. This would explain both your lowered fuel economy as well as your trouble codes.
08-22-2001, 07:06 PM
#3
Senior Member
Join Date: Sep 2000
Posts: 4,601
Hell
Originally posted by NYCe MaXiMa
I am getting two trouble codes, both pointing to the same problem. 0705 and 0309....
0705 = EVAP control system leak?
0309 = EVAP canister vent control valve open
How does this EVAP canister work, does it clean the gasoline of foreign substances or what? I understand it involved emissions..
Also, I wanted to know if these things can lead to poor gas milage? I think the ghost of poor fuel economy hunts me, I will get only around 270 miles on this tank of gas... It's either that or I am a REALLY aggressive driver, although I never get bad gas milage on other cars.
Can anyone help me out? I am not quite sure that I understand what the sticky at the top states. I want to know if it can cause poor fuel economy as well...
thanks.
Steve
I am getting two trouble codes, both pointing to the same problem. 0705 and 0309....
0705 = EVAP control system leak?
0309 = EVAP canister vent control valve open
How does this EVAP canister work, does it clean the gasoline of foreign substances or what? I understand it involved emissions..
Also, I wanted to know if these things can lead to poor gas milage? I think the ghost of poor fuel economy hunts me, I will get only around 270 miles on this tank of gas... It's either that or I am a REALLY aggressive driver, although I never get bad gas milage on other cars.
Can anyone help me out? I am not quite sure that I understand what the sticky at the top states. I want to know if it can cause poor fuel economy as well...
thanks.
Steve
The EVAP system helps to reduce air pollution by minimizing the amount of fuel lost directly to the atmosphere by evaporation. The canister contains charcoal granules which adsorb gasoline vapor and store them temporarily until the engine intake manifold vacuum draws them off.
A malfunction of the EVAP system is unlikely to cause the high fuel consumption you report. However, it may be a useful clue pointing to a fuel leak.
Miles per tank is not an accurate way to measure or express fuel usage. Miles per gallon is.
08-22-2001, 07:15 PM
#4
Senior Member
Join Date: Sep 2000
Posts: 4,601
DTC 0309
Diagnostic Trouble Code 0309 points to a problem with the EVAP Canister Vent Control Valve. EVAP = EVAPorative emissions control system. This is the system which seeks to minimize air pollution which results from evaporation (as opposed to incomplete combustion) of gasoline.
The EVAP CVCV is located on the EVAP canister (underneath the vehicle near the left rear tire) and is used to seal the canister vent. It has one hose connection and one two-wire electrical connector. The solenoid in the EVAP CVCV responds to signals from the ECM. When the ECM sends an ON signal, the coil in the solenoid valve is energized. A plunger then moves to seal the canister vent. The ability to seal the vent is a necessary part of the diagnosis algorithms for other evaporative loss system components. This solenoid valve is used only for diagnosis, and usually remains open. When the vent is closed, under normal purge conditions, the evaporative loss system is depressurized allowing "EVAP Control System (Small Leak)" diagnosis. Since this part is used only for brief emissions tests the vehicle will usually start and run well despite a Service Engine Soon warning light on the dashboard.
The malfunction is detected when the EVAP CVCV remains open when it should be closed.
Possible causes include ...
- EVAP CVCV is defective
- EVAP control system pressure sensor and its circuit is faulty
- Blocked rubber tube to EVAP CVCV
- Water separator
- EVAP canister is saturated with water
- Vacuum cut valve
The EVAP CVCV may be bench tested. Remove it from the vehicle (one hose, one connector, two bolts). Verify that air may pass freely through the valve. Then use a pair of fused test leads to apply 12 volts to the terminals to energize the solenoid. Verify that air does not pass freely through the valve. If the CVCV fails these tests, try cleaning it with WD-40 and compressed air. If this fails to free it up, replace the valve. When you install a CVCV (the original or a replacement) always use a new O-ring.
The EVAP canister may be removed from the vehicle and upended to drain accumulated water. After draining the canister, weigh it. If the canister (with the EVAP CVCV attached) weighs more than 4.0 pounds, replace it.
The EVAP CVCV is located on the EVAP canister (underneath the vehicle near the left rear tire) and is used to seal the canister vent. It has one hose connection and one two-wire electrical connector. The solenoid in the EVAP CVCV responds to signals from the ECM. When the ECM sends an ON signal, the coil in the solenoid valve is energized. A plunger then moves to seal the canister vent. The ability to seal the vent is a necessary part of the diagnosis algorithms for other evaporative loss system components. This solenoid valve is used only for diagnosis, and usually remains open. When the vent is closed, under normal purge conditions, the evaporative loss system is depressurized allowing "EVAP Control System (Small Leak)" diagnosis. Since this part is used only for brief emissions tests the vehicle will usually start and run well despite a Service Engine Soon warning light on the dashboard.
The malfunction is detected when the EVAP CVCV remains open when it should be closed.
Possible causes include ...
- EVAP CVCV is defective
- EVAP control system pressure sensor and its circuit is faulty
- Blocked rubber tube to EVAP CVCV
- Water separator
- EVAP canister is saturated with water
- Vacuum cut valve
The EVAP CVCV may be bench tested. Remove it from the vehicle (one hose, one connector, two bolts). Verify that air may pass freely through the valve. Then use a pair of fused test leads to apply 12 volts to the terminals to energize the solenoid. Verify that air does not pass freely through the valve. If the CVCV fails these tests, try cleaning it with WD-40 and compressed air. If this fails to free it up, replace the valve. When you install a CVCV (the original or a replacement) always use a new O-ring.
The EVAP canister may be removed from the vehicle and upended to drain accumulated water. After draining the canister, weigh it. If the canister (with the EVAP CVCV attached) weighs more than 4.0 pounds, replace it.
08-22-2001, 07:17 PM
#5
Re: Hell
Originally posted by Daniel B. Martin
Why the hell do you put hell in the subject line? Do you think it makes your post more interesting or more readable? It doesn't.
The EVAP system helps to reduce air pollution by minimizing the amount of fuel lost directly to the atmosphere by evaporation. The canister contains charcoal granules which adsorb gasoline vapor and store them temporarily until the engine intake manifold vacuum draws them off.
A malfunction of the EVAP system is unlikely to cause the high fuel consumption you report. However, it may be a useful clue pointing to a fuel leak.
Miles per tank is not an accurate way to measure or express fuel usage. Miles per gallon is.
Why the hell do you put hell in the subject line? Do you think it makes your post more interesting or more readable? It doesn't.
The EVAP system helps to reduce air pollution by minimizing the amount of fuel lost directly to the atmosphere by evaporation. The canister contains charcoal granules which adsorb gasoline vapor and store them temporarily until the engine intake manifold vacuum draws them off.
A malfunction of the EVAP system is unlikely to cause the high fuel consumption you report. However, it may be a useful clue pointing to a fuel leak.
Miles per tank is not an accurate way to measure or express fuel usage. Miles per gallon is.
TarHeelMax: thanks.
Daniel: I appologize for using the word "hell" didn't realize it may bother someone. No I don't think it makes the post more readable or interesting, just threw it up expressing some frustration I guess, just got the car and here comes the Service Engine Soon light.
Yes, miles per fuel tank is not accurate, but it's a rough estimate, basically I just thought, the TOP marker on the fuel gauge to the middle is close to a half of tank, I got 130 miles from the top of the tank to the middle marker, estimating roughly it's still low. I'm waiting to run the tank until the light comes on and fill it back up and see how much miles I got from this tank and divide it by how much fit in it.
thanks for the feedback.
08-22-2001, 07:20 PM
#6
Senior Member
Join Date: Sep 2000
Posts: 4,601
Excessive fuel consumption
Your car is using too much fuel. These possibilities exist:
- you are burning it
- you are leaking it
- someone is stealing it
- you are using gasohol
Burning it...
- fuel injectors are sticking open
- "tired" Oxygen Sensors
- bad fuel pressure regulator
- obstructed fuel return line
- clogged air cleaner filter
- bad Engine Coolant Temperature Sensor
- stuck-open thermostat (engine never goes into closed-loop mode)
- transmission defect (never shifts into fourth gear)
- dragging brakes
Leaking it...
Search for fuel leaks by sight and odor. However, some fuel leaks are so
tiny that they escape the human senses. One way to find them is to have
your mechanic use his exhaust gas analyzer. Switch the tester to HC
(hydrocarbons) and then pass the probe along the entire fuel system,
starting at the fuel tank, forward along the fuel lines, past the filter,
all around the engine, then along the return line and back to the tank.
The tester is far more sensitive than the human eye or nose. When the
probe passes near a tiny leak the reading will abruptly increase.
Stealing it...
Perhaps someone is stealing small quantities of fuel, not for its financial
value but as a prank. Install a locking fuel filler cap.
Gasohol...
- You may have been buying gasohol rather than gasoline, without realizing it.
- You may live in one of those regions which is required to sell oxygenated
fuel.
Now that MTBE is in disfavor, gasohol is the most common oxygenated fuel.
Alcohol has a lower energy density than gasoline.
- you are burning it
- you are leaking it
- someone is stealing it
- you are using gasohol
Burning it...
- fuel injectors are sticking open
- "tired" Oxygen Sensors
- bad fuel pressure regulator
- obstructed fuel return line
- clogged air cleaner filter
- bad Engine Coolant Temperature Sensor
- stuck-open thermostat (engine never goes into closed-loop mode)
- transmission defect (never shifts into fourth gear)
- dragging brakes
Leaking it...
Search for fuel leaks by sight and odor. However, some fuel leaks are so
tiny that they escape the human senses. One way to find them is to have
your mechanic use his exhaust gas analyzer. Switch the tester to HC
(hydrocarbons) and then pass the probe along the entire fuel system,
starting at the fuel tank, forward along the fuel lines, past the filter,
all around the engine, then along the return line and back to the tank.
The tester is far more sensitive than the human eye or nose. When the
probe passes near a tiny leak the reading will abruptly increase.
Stealing it...
Perhaps someone is stealing small quantities of fuel, not for its financial
value but as a prank. Install a locking fuel filler cap.
Gasohol...
- You may have been buying gasohol rather than gasoline, without realizing it.
- You may live in one of those regions which is required to sell oxygenated
fuel.
Now that MTBE is in disfavor, gasohol is the most common oxygenated fuel.
Alcohol has a lower energy density than gasoline.
08-22-2001, 07:37 PM
#7
All YOUR grammer belong to me
Join Date: Jul 2001
Posts: 7,400
Re: Excessive fuel consumption
The moderators here should make this a STICKY. Everything Daniel says is very detailed and very accurate.
Someone follow Daniel around.
Seriously, though, If we made everything Daniel says a sticky, all our maxima problems would be solved, tons of these everyday posts would be eliminated, and Daniel would get a much needed vacation.
Someone follow Daniel around.
Seriously, though, If we made everything Daniel says a sticky, all our maxima problems would be solved, tons of these everyday posts would be eliminated, and Daniel would get a much needed vacation.
08-22-2001, 07:54 PM
#8
Re: Excessive fuel consumption
Originally posted by Daniel B. Martin
Your car is using too much fuel. These possibilities exist:
- you are burning it
- you are leaking it
- someone is stealing it
- you are using gasohol
Burning it...
- fuel injectors are sticking open
- "tired" Oxygen Sensors
- bad fuel pressure regulator
- obstructed fuel return line
- clogged air cleaner filter
- bad Engine Coolant Temperature Sensor
- stuck-open thermostat (engine never goes into closed-loop mode)
- transmission defect (never shifts into fourth gear)
- dragging brakes
Leaking it...
Search for fuel leaks by sight and odor. However, some fuel leaks are so
tiny that they escape the human senses. One way to find them is to have
your mechanic use his exhaust gas analyzer. Switch the tester to HC
(hydrocarbons) and then pass the probe along the entire fuel system,
starting at the fuel tank, forward along the fuel lines, past the filter,
all around the engine, then along the return line and back to the tank.
The tester is far more sensitive than the human eye or nose. When the
probe passes near a tiny leak the reading will abruptly increase.
Stealing it...
Perhaps someone is stealing small quantities of fuel, not for its financial
value but as a prank. Install a locking fuel filler cap.
Gasohol...
- You may have been buying gasohol rather than gasoline, without realizing it.
- You may live in one of those regions which is required to sell oxygenated
fuel.
Now that MTBE is in disfavor, gasohol is the most common oxygenated fuel.
Alcohol has a lower energy density than gasoline.
Your car is using too much fuel. These possibilities exist:
- you are burning it
- you are leaking it
- someone is stealing it
- you are using gasohol
Burning it...
- fuel injectors are sticking open
- "tired" Oxygen Sensors
- bad fuel pressure regulator
- obstructed fuel return line
- clogged air cleaner filter
- bad Engine Coolant Temperature Sensor
- stuck-open thermostat (engine never goes into closed-loop mode)
- transmission defect (never shifts into fourth gear)
- dragging brakes
Leaking it...
Search for fuel leaks by sight and odor. However, some fuel leaks are so
tiny that they escape the human senses. One way to find them is to have
your mechanic use his exhaust gas analyzer. Switch the tester to HC
(hydrocarbons) and then pass the probe along the entire fuel system,
starting at the fuel tank, forward along the fuel lines, past the filter,
all around the engine, then along the return line and back to the tank.
The tester is far more sensitive than the human eye or nose. When the
probe passes near a tiny leak the reading will abruptly increase.
Stealing it...
Perhaps someone is stealing small quantities of fuel, not for its financial
value but as a prank. Install a locking fuel filler cap.
Gasohol...
- You may have been buying gasohol rather than gasoline, without realizing it.
- You may live in one of those regions which is required to sell oxygenated
fuel.
Now that MTBE is in disfavor, gasohol is the most common oxygenated fuel.
Alcohol has a lower energy density than gasoline.
I've gone through this fuel consumption problem with my 3rd gen which (when measured correctly) got 13-14 mpg in any kind of driving. Had the injectors cleaned and 1 replaced by the dealer. Also replaced; o2 sensor, Fuel pressure regulator, spark plugs, air and fuel filters, rubber vacuum hoses leading from fuel filter, cleaned Throttle position sensor, throttle body, checked MAF sensor, Coolant temp sensor, flushed coolant. Had a fresh rebuilt transmission in the car as well. None of those things really made a difference, and I couldn't pass the inspection either. But I am not going to look back on that car since it's gone now.
I think I can rule out the gasohol idea and someone stealing it. However the fuel leak I'll look into, never knew a mechanic can find a leak the way you described, I've brough my 3rd gen to various shops and none of them ever done anything like that and failed in finding the problem or suggested repairs of things I've already replaced. once again, thanks for the feedback.
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