Blow Off Valve

The blow off valve is an important part of any working turbocharged engine. The blowoff valve works as a pressure release system which is responsible for stopping a compressor surge from occurring and minimizing the amount of wear that the engine receives from heavy usage.

The blow off is also referred to as the hooter valve, and is sometimes mistaken for the dump valve. The blowoff valve is not the same as the dump valve, but the tasks that each must complete are similar. The dump valve does the same job as the blow off valve but it doesn’t send air out into the atmosphere. The dump valve just makes the air circulate continuously through the system.

How the Blowoff Valve Works
The blowoff valve is attached to the intake manifold with a vacuum hose connecting the two. The intake manifold follows the throttle plate which plays an important role in the blowoff valve working properly. Once the throttle closes, a manifold vacuum is created inside the intake manifold. This will cause the blow off valve to be sucked open. Any excess of pressure will either be vented out into the atmosphere or will be sent through the intake to be circulated.

Compressor Surge – What It Is
Compressor surges are very serious issues that some cars suffer from at some point. This usually occurs with turbocharged engines that don’t have proper ventilation, and happens when the throttle is lifted. Once the throttle plate closes, high pressure area gets stuck within the intake system because of the throttle. The air is then forced into the compressor where the compressor wheel will quickly slow down and could possibly stop working completely.

After everything occurs, you may be able to hear a sound similar to flapping air. This will ultimately lead to turbo lag if you attempt to accelerate right after the compressor surge occurs. The compressor surge issue can be a major problem but it rarely occurs in turbocharged engines that have a blowoff valve.

Problems with the Blow off Valve
If there is a mass airflow sensor in place and it’s found before the blowoff valve, it can cause issues with the engine control unit. If this is the case, it could lead to an excess of fuel being used. This is due to the fact that some air isn’t taken away from the total intake amount in the engine control unit when the mass airflow sensor is set up as so.

This particular set up will cause the engine to use a mixture that contains a higher concentration of fuel for a few moments. This will occur every time the blowoff valve is put into action. The amount of fuel that is lost may not be a noticeable amount but it can definitely add up over time. However, the main issue isn’t with the lost gas, but rather what the high concentration of gas can do to your vehicle.

Your vehicle’s engine could hesitate or stall once the throttle is closed due to a rich mixture of gas. This problem will only get more severe over time and is worsened when the boost pressure is increased. This may only be a problem that has random, and irregular, occurrences but if you find your vehicle is regularly hesitating or stalling it could cause other problems.

If these problems continue frequently over time, the spark plugs can malfunction and it will lead to the catalytic converter not being able to work anymore. This is because there will be a build up of carbon and fuel (that hasn’t been burnt) in the catalytic converter and this will cause the catalytic converter to overheat if the case is severe enough.

How to Solve the Problem
The easiest way to stop any serious problems from occurring would be to decrease the amount of boost pressure. This will then lower the amount of venting volume that’s necessary and won’t cause for as much of a miscalculated number to show up in the engine control unit. Vehicles with the mass air flow sensor are also usually designed with the ability to send the air back to the intake and circulate again.

Another method of solving this problem would be to swap the fuel metering system for a manifold absolute pressure sensor. You may need to purchase a special engine control unit for this replacement though. Replacing the fuel metering system with a manifold absolute pressure sensor is the best option to make sure your blowoff valve works properly when set up with a mass air flow sensor.

The new sensor will be able to evaluate the total amount of pressure within the manifold and can provide accurate information once the blowoff valve vent is in use. This will allow for the engine control unit to work with the right amount of fuel that’s necessary. By making this change, you will remove the possibility of ruining your catalytic converter because of the blowoff valve.