While using a vehicle, people come across the issue of engine misfire and vehicle starting problem or rough vehicle idle at some point in time.
This issue would be related to several parts associated with the engine but many times the root cause of the issue may be as simple as a bad evap purge valve.
Also often people want to be sure that there are no issues in the EVAP emission control system when it is time to do a vehicle emission smog test.
There are different parts of the EVAP system like a fuel tank with a pressure sensor, Charcoal canister, purge control valve, vent solenoid valve, and a pressure switching valve.
Each part has its importance in the proper functioning of the EVAP system. Failure of parts to perform efficiently would lead to vehicle emission test fail.
The problem with the EVAP system can be easily rectified if we follow general hygiene cleaning of EVAP system parts especially the valves involved.
Here in this article, we are going to discuss the cleaning of the evap purge valve.
Table Of Contents
- 1 What Is EVAP System?
- 2 Why Is My Purge Valve Clicking?
- 3 What Causes A Canister Purge Valve To Go Bad?
- 4 Can Purge Valve Be Cleaned? How To Do It?
- 5 How To Test Purge Valve?
- 6 Conclusion
What Is EVAP System?
We all know that gasoline is a highly volatile compound. EVAP emission control system is provided on gasoline vehicles to regulate, accumulate and consume the gasoline vapors effectively which otherwise gets emitted to the atmosphere.
Gasoline vapors generation can be regulated by the use of a tank pressure control valve which maintains certain pressure in the fuel tank before it gets released to the next device which is a charcoal canister.
This is because gasoline vapors generation will be less when it is under pressurized condition.
A charcoal canister accumulates the gasoline vapors exiting the fuel tank and stores them in the charcoal particles by adsorption.
These stored vapors are pulled into the engine combustion chamber provided the purge valve allows the engine vacuum to reach the charcoal canister.
The purge valve gets an input signal from ECU (Electronic Control Unit) which checks for few favorable conditions under which gasoline vapors can be purged safely into the engine without affecting its performance
The gasoline vapors traverse from charcoal canister to engine intake manifold via. purge valve and mixes with the main air-fuel mixture injection and participates in the combustion process.
Why Is My Purge Valve Clicking?
When you happen to open the vehicle’s bonnet, you may hear purge valve clicking sound intermittently. So what exactly happens when we say that the purge valve is activated by ECU?
For this, we need to understand, how the purge valve works.
Purge valves usually consist of a spring and plunger arrangement with valve seats or O-rings for sealing the outlet path.
It also has socket terminals whose ends are connected to a coil of wires wound around the plunger inside. Terminals are connected to ECU by the wiring harness.
The purge valve is usually closed due to the spring action so that plunger normally rests against the valve seat and ensures proper sealing.
When predefined conditions which are programmed in ECU are satisfied, ECU sends a voltage signal to the purge valve.
This voltage input to the terminals and coil of wires creates an electromagnetic field around the plunger and it energizes the plunger thereby lifts it. This produces an audible clicking sound.
Due to this, the plunger retracts from the valve seat and the sealed path gets opened so that it connects the engine intake manifold vacuum to the charcoal canister to pull away the gasoline vapors from the canister.
The purge valve doesn’t remain open continuously, it works in duty cycle for some preset time or conditions, so that you would be able to notice clicking sound frequently but intermittently from the purge valve.
If the purge valve remains open continuously then it would affect the main stoichiometric air-fuel ratio of the combustion mixture.
Hence continuous purging is not done and so the continuous purge valve clicking for a longer time means some issue with ECU or its wiring connection.
What Causes A Canister Purge Valve To Go Bad?
Usually, the evap purge valve lasts for the life of the vehicle but over a while, it may start to underperform due to the following reasons,
Valve seat damage
Due to the purge valve duty cycle and the repeated clicking of the purge valve by ECU, the internal plunger retracts and regains the original position of resting against the valve seat.
So the plunger intermittently loses contact with the valve seat and creates a small impact load whenever it establishes contact.
This leads to wear and tear of the valve seat at the interface between the plunger and the valve seat.
This would create a leakage path and start leaking vacuum even in the absence of ECU open signal.
Charcoal particles getting entangled in purge valve
The charcoal Canister sometimes gets flooded with liquid gasoline due to vapor saturation or vapor condensation.
This affects the charcoal particles which lose their porosity and becomes a fine powder.
If the charcoal filter is damaged, then these fine powders of charcoal reach the evap purge control during purging operation and get entangled at valve seats of purge valve or stuck into the springs.
This leads to valve leak & valve stuck open problems in the purge valve due to the inability of the spring to regain its original position.
Accumulation of carbon soot and insertion aids at valve seat
The gasoline vapor has several hydrocarbon compounds having various molecular weights.
These hydrocarbons and other foreign particles when they pass through the purge valve openings get accumulated at different locations of the purge valve.
The predominant location is the purge valve seat. The foreign matters will not get accumulated on the valve seat uniformly.
Hence the plunger establishes a non-uniform sealing interface with the valve seat and creates a valve leak path.
The vacuum hose insertion aids on purge valve nozzle sometimes get through the nozzle port and reach the valve seat and creating a sticky improper sealing interface.
Damaged electrical wires
The wiring harness which sends signals from ECU to purge valve sometimes may get a break or get short, owing to its durability life making the purge valve go bad electronically.
When the purge valve does not respond to ECU signals it remains closed and does not serve its purpose and will fail the vehicle SMOG test.
Because during the SMOG test, when ECU checks all valves for confirming their function, the purge valve will be out of order.
Can a bad purge valve causes vehicle performance issues like a rough idle, misfire, loss of power, stop a car from starting, Check Engine Light (CEL) on the dash? The answer is why not? It will.
In case of a bad purge valve or vacuum leaking valve, the engine vacuum would be constantly applied to the charcoal canister and endless purging would be taking place.
So the engine air-fuel ratio will be continually affected and would probably face above vehicle problems which normally would happen in the absence of an evap purge valve in the EVAP system circuit.
Often the bad purge valve will not result in vehicle issues instantly and you may not notice the symptoms initially but it may later manifest into engine problems.
Can Purge Valve Be Cleaned? How To Do It?
As explained above, the purge valve may go bad due to various reasons, most of the time the issue is either valve leak or valve stuck open.
So if you are looking for ways to clean the purge valve to get rid of problems associated with it, you can follow the below steps and procedures.
1) A purge valve is usually located close to the air intake manifold and connects it to the charcoal canister. You may trace the vacuum hoses to and fro to confirm the purge valve.
2) Once the purge valve is traced, then disengage the electrical coupler which connects the purge valve to ECU.
For this, usually, a catch or snap-fit kind of feature is provided on a plastic coupler. To decouple the connections, simply press those features and pull them out simultaneously.
Usually, there used to be foolproof features to ensure coupler fitment in one particular orientation and direction to prevent reverse polarity connections.
3) Remove the vacuum hose clamps which are fitted over the inlet and outlet nozzles.
4) Disengage the vacuum hoses which run towards the charcoal canister and air intake manifold. Replace vacuum hoses, if they are found cracked.
5) Disassemble the mounting screws of the purge valve to remove it.
In some purge valve arrangement, if you view through the nozzle holes under bright light, you may notice black carbon soot getting settled inside.
6) After removing the purge valve, first dismantle the purge valve assembly if it can be easily openable type like unfastening some screws or removing some crimping’s.
Then you can access internal parts of the valve and spray cleaners on sealing interface areas.
Check how the internal parts are assembled before dismantling, so when the time comes to reassemble you would not end up making blunders and kill the valve.
Probably labeling the hose and electrical connections with masking tape will prevent the wrong fitment.
7) If the purge valve body is made by joining different pieces by hot plate welding or molding, then it will be difficult to break open.
If you do not want to mess up with the purge valve, then, in that case, you may clean it by spraying cleaners into nozzles of the purge valve.
8) In general, before spraying cleaners, if some hard black soot-looking gunk or deposits seems to be accumulated inside the valve, you may notice that the cleaning solution comes clean out of nozzles and not doing its job.
In that situation, you may try poking with some objects to work around the hard deposits to loosen it, till you observe an unclean solution coming out from the nozzles of the valve.
Stop poking until you see shiny, clean metal stare back at you.
9) Remember that the purge valve electrical socket terminals shall not be exposed to any cleaners or water, otherwise, the electrical connection would rust or get short and may spoil everything.
10) Once the cleaner is sprayed into the valve nozzles, keep it soaking for about 20 minutes and after that, you probably would notice that the black particles come out of the purge valve.
After reassembling the purge valve you would notice the engine running better than earlier.
Similarly, you can clean the evap vent solenoid valve with the cleaners, if it is covered with dirty gunk all around and inside.
These vent solenoid valve usually sits on the top of the charcoal canister and are normally open but when it goes bad it affects the fuel system venting and would cause to throw Check Engine Light (CEL) on the dash.
Below are the cleaners recommended to clean the purge valve and vent solenoid valve.
How To Test Purge Valve?
To confirm whether there is any problem with the evap purge valve. First, we should know how to test the purge valve.
Below are the tests that need to be done to test purge valve
Is the purge valve retaining vacuum?
In this test, you will check whether the purge valve is leaking. There are two nozzles on the purge valve.
One is the inlet nozzle through which the gases go inside and other the is the outlet nozzle through which the gases come out.
These two nozzles are usually disconnected from each other by sealing arrangement unless activated by an external voltage source.
Connect hand vacuum pump to the inlet nozzle of purge valve but keep the outlet nozzle open to atmosphere.
Now apply a small amount of vacuum (say 15 inch. Of Hg/50 kPa) and the purge valve should hold the vacuum without any leak.
Is the Purge valve releases vacuum when energized?
There are two ways in which this test can be conducted. one is by using vacuum pump but if it is not available, you can also try blowing air.
1) Using vacuum pump
Whenever the ECU sends signals to the purge valve, it shall open.
In the above test, when you connect the purge valve terminals to battery voltage by using alligator jumper wires (say 9V), the valve shall open and the two nozzles will be connected & the vacuum shall drop immediately to 0 kPa.
2) Blowing air
In the absence of a vacuum pump, you could do this test by blowing air.
Connect two alligator jumper wires on the two pins and connect one lead to the negative on the battery.
Try blowing into one of the nozzles, air should not flow through.While attempting to blow in one end, connect the other lead to the positive of the battery, air should now flow.
Release positive lead and airflow should be blocked.
Do you hear a clicking sound?
You would hear a continuous audible clicking sound when voltage is applied intermittently across the purge valve terminals.
It means the purge valve spring is getting energized properly.
Is the purge valve stuck open?
In the above sound test, the purge Valve shall close when the voltage is removed.
If you are not hearing continuous clicking sound, it means the valve is stuck open.
You can also test this by applying a vacuum without applying a voltage to the valve.
The vacuum will not get generated since the valve is stuck open.
Check purge valve circuit continuity
Set the multimeter to continuity test. Connect multimeter probes to the terminals of the purge valve.
The multimeter shall produce a continuous sound which confirms that the wiring circuit is continuous.
Check purge valve wiring resistance
Set the multimeter to read the resistance. Connect multimeter probes to the terminals of the purge valve.
Resistance across the terminals shall be in the range of 20 to 50 Ω depending upon the manufacturer.
If the multimeter reads infinite resistance, it means the circuit is broken somewhere.
The Purge valve is an important part of the EVAP emission control system.
Due to its frequent engagement, while the vehicle running, the performance of the purge valve reduces over some time due to the durability limitation of any moving mechanism for that matter.
With the above information, you may check and analyze the root cause of the problem, and based on that you may decide to clean the purge valve or look for buying a new one.
It is worthy to inspect the purge valve so that whenever you face some other related problem you can try to fix, before going for an easy solution of replacing the purge valve.
Even though the purge valve doesn’t cost more, if simple cleaning of the purge valve is what may make the engine cabin lamp go off or fix other vehicle problems, then why not give it a try!