BMW is one of the first auto manufacturers who figured out that controlling the path air takes as it travels through the engine can yield better performance. Hence the DISA valve was invented. DISA stands for ‘Differenzierte Sauganlage,’ or in English – Differentiated intake system.
The valve itself found on a variety of older BMW engines that have found their way into 5-series, 3-series, X3 and X5, and even Z series cars. It’s apparent that BMW went on to apply this technology in most of their offer spanning from 1995 when it first appeared in E39 5-Series, while the last family of engines to sport a DISA valve is the M50 installed in E60 5-Series.
What many owners of the BMWs mentioned above will tell you, is that DISA valves also have a rather dark side to them. This component can cause a variety of problems that may lead you on a wild goose chase trying to figure out why your vehicle is barely limping along. Today we’ll dig deep into this matter, do a rundown of most common symptoms and share some tips on when to replace it.
What is a DISA Valve?
Controlling the path of air as it moves through the intake plenum has proven to be a good way to regulate performance. DISA valve does precisely that. It is essentially an electronically controlled flap that opens and closes depending on what the ECU is sending back. By changing the geometry of air as it runs through the plenum, this valve alone can increase or decrease the pressure of air fed into the engine.
Mind you, this is a pretty crude explanation of what is actually going on in there. To better explain how this thing works, we need to understand how air behaves as it enters the engine.
Intake Tuning – The Delicate Art of Perfect Timing
Before air gets pumped into the engine, it needs to go through your intake manifold. This seemingly simple box ultimately distributes the air to all of the cylinders, which then suck it in on the intake stroke. Here’s the thing.
As the intake valve closes after sucking in a healthy amount, the air that is being cut off by the closing valve bounces back towards the plenum. It travels to the very back of the plenum, bouncing off again and heading straight towards that same intake valve.
One of the key principles of efficient engine performance is to time the valves so that they open up exactly when that bouncing air comes right back. In a fixed RPM engine, that wouldn’t be an issue. However, when you’re dealing with a motor that needs to be efficient at low RPMs and high RPMs, you run into a problem.
A DISA valve is primarily there to extend or shorten the volume of the plenum. When your engine is running in lower RPMs, the valve is closed. This means that the excess air that ran into a closing valve can now take more time to make its way back. When the RPMs are high, and the intake valve opens much more frequently, the DISA valve opens and shortens the time it takes for air to bounce back.
Fortunately for everyone, the ECU takes care of calculating how much the DISA valve needs to be open.
How Does DISA Work Exactly? – Visualizing the Intake System
Let’s take our explanation a step further and help you visualize just how these valves work. If you’re a grease monkey like most of us are, you’ll love this part. BWM engineers from Munich sat down and created what is essentially an ingenious system of tubes and chambers that route the air towards the intake valves.
The entire intake can be described as two separate loops that sit on top of each other. This is also why the throttle body on these engines is located at the bottom rather than on top. The entire system we’ve just described can be regulated with that single DISA valve. Let’s look at the graphic below and explain what’s going on.
When the engine is running at low RPM, the valve is closed, thus forcing the air to take a long way around through resonance manifolds. As a result, your car has better low-end torque and fuel efficiency.
Let’s say that you’re on a highway and you want to pass the person driving in front of you. As you downshift, you’re pushing the engine into a higher RPM range. This is where the DISA valve starts opening up, allowing the air rushing into the engine to take a shortcut to the intake valves.
At this point, all of the resonance tubes are opened wide, allowing the maximum volume of air to reach the intake valves and ultimately get sucked into the cylinders.
When presented like this, it’s easy to understand why these valves are so crucial for the optimal performance of your engine. BMW went on to design more complex intake systems in later engines that incorporate another intake circuit. This was done to tackle the lack of mid-range power as the earlier DISA Valves generally covered only the lower end and top end of the RPM curve.
Recognizing a Failing DISA Valve on your BMW – Symptoms, and Troubleshooting
We’ve mentioned how DISA valves have a very dark side to them? As many owners of BMWs with DISA fitted engines will tell you, this single valve can be the bane of your existence. The main issue with DISA valve failure is that it can lead to poor fuel efficiency, or it can nuke the engine. Chilling, right? Yeah, that plastic flap that opens and closes can literally disintegrate, sending pieces of plastic straight into your engine. You can only imagine the havoc that can cause.
Fortunately for all of us, that happens very rarely. However, the fact that it’s a possibility at all means that you need to be extra vigilant when it comes to recognizing a failing DISA valve on time.
Little Valve, Big Trouble – Troubleshooting a Failing DISA Valve
Before we get into the specifics, it’s important to know that DISA Valves were never designed to last for more than 70,000 to 100,000 miles. In other words, if you got your BMW brand new and planned on owning for a while, you’re most likely going to have to deal with this.
More importantly, if you just got yourself a used BWM from this era, definitely check this valve often. Mind you, these mileage estimates don’t take into account the condition of the car, how it was used, what environment it operated in, etc.
The first things to usually that go bad on a DISA valve are the seals. As the flap closes, it relies on the seal to keep any excess air from moving through it. When this seal fails, you’ll get excess air in the engine, which ultimately results in poor fuel economy. But wait, there’s more!
That’s not the only seal that can go bad on you. DISA valve housing seal can also fail over time. Since this entire thing sits right on the intake, a bad seal means a vacuum leak. Now you have air that isn’t accounted for by the Mass Airflow System, meaning that your ECU is not aware of it either.
Since it’s using the info from the MAF sensor to balance out the fuel mixture, this excess air will cause rough engine performance and poor fuel economy. More extreme cases could lead to a potentially dangerous lean condition, and that is something you’ll want to avoid.
How to Tell If your DISA Valve is Failing?
One of the telltale signs of a dying DISA valve is its death rattle. Page your mechanic or roll up your sleeves if you hear it. The rattle starts off subtle and gets worse over time. Now, there’s plenty of things that can start rattling inside the engine bay of your BMW. The easiest way to figure out if it’s the DISA valve is to unplug the valve. Once it loses power, the valve will succumb to the rushing air and get stuck in the open position, preventing it from rattling.
It is also possible to get a check engine light if your DISA goes bad. Mind you, and the engine will most likely run poorly at this point, so you should already be wondering what’s wrong with your car.
DISA Valve Replacement Tips
BMW has installed DISA valves across a wide range of engines. The M50 family is notorious for having DISA valve problems. To make things even trickier, not all of these valves were made the same. Since they’ve been installing them since 1995 to roughly 2010, BWM went through several generations of this valve in their cars.
The very first thing you should do is figure out what type of DISA valve you have. This is important because you may just need a simple O-ring. For example, the M52 engine features a DISA valve where you can buy the O-ring as a spare part. We carry this item under the parts number 11617504543. If the valve on your DISA works but you’re getting all of the symptoms, the chances are that you just need this inexpensive part. However, there are instances where you will have to get the whole valve instead.
The fortunate thing is that replacing a DISA valve is not that difficult on most engines. We’ll take the M52 mentioned above as an example. This engine was a popular choice in the E39 5-Series, making it a perfect specimen for our little tutorial here. You won’t need to go through 100 pages of a workshop manual for this repair.
Finding and Replacing the DISA Valve on an M52 Engine
Once you pop the hood of your vehicle, take a closer look at the right side of the engine. That is where you’ll find the intake manifold. Bolted right onto the manifold itself is a small black box. That is the DISA valve housing.
The very first thing you’ll need to do is disconnect the wire harness from the valve. The jack has a little metal clip that you’ll need to press in order to pop it off. This is also the first step to troubleshooting your DISA valve.
Now that the valve has been disconnected, you’ll have to remove the intake hose that’s in the way. This is simple enough to do and requires only the basic tools.
The hose is held in place by two clamps – one on each end. Start by removing the bottom clamp first as it is harder to reach. Once that is done, remove the top clamp that connects the hose to the MAF sensor. We suggest that you remove the MAF sensor from the air filter box as well as it greatly increases the amount of room you have got to work with.
One very important tip! When you remove the air intake hose, make sure to cover the actual intake with a rag or a plastic bag. You’ll be working with tools and removing bolts right over it, and the last thing you need is something falling into it. That’s an easy way to brick the engine.
Now that you have clear access to the valve itself, you’ll need Torx 14 bits. The valve is held in place by two bolts – one at the 6 o’clock position and one at 2 o’clock position. Again, cover your intake as it’s super easy to drop these two bolts right into the intake hole.
With the bolts removed, start wiggling the valve up and down to break the seal. It should come right out at this point.
To replace the valve, simply insert the new parts where the old used to be, and repeat the removal steps in reverse.
Here’s a step by a step video tutorial that shows this process.
To Rebuild or to Replace?
As we’ve mentioned before, some generations of DISA valves can be rebuilt while some need to replaced completely. In case yours can be rebuilt, the question is whether you should do this?
Rebuilding a DISA valve can be a fun DIY project, given that you know what you’re doing. We will stick to our M52 engine and its generation of DISA valves for this little case study. There are two parts of this valve that are prone to failure over time – the O-ring and the actual flap mechanism. If the actual mechanism that holds the valve open under vacuum fails, you’ll have to replace the whole thing.
Doing a complete valve rebuild with aftermarket flaps and O-rings is not that hard at all. You can get it done with standard tools in under an hour. Truthfully, this is probably the cheapest way to get your vehicle sorted out, at least initially.
The main problem with rebuild kits is that you’re introducing an unknown variable into a very delicate equation. Aftermarket flaps that come in these parts kits use different plastics and are often built to different specs. They fit, but how well do they work?
We’ve already talked about the worst-case scenario. There’s nothing worse than hearing the sound of your engine munching on a disintegrated DISA flap as you’re cruising down the highway. Are you willing to risk that type of damage to your vehicle? That is essentially the question you need to ask yourself.
We strongly support swapping the O-ring if that’s the only thing wrong with your valve. However, we can’t, in good conscious get behind rebuild kits. The risks are just not worth the few dollars you’ll save.
At the end of the day, replacing a DISA valve is neither complicated nor expensive. However, if you ignore the problem, you’re running a risk of severely damaging the engine in the long term. Short term, you’re going to be suffering poor engine performance while stopping at every other gas station on your way to and from work. If you have any questions regarding DISA valves in your BMW, give us a call or contact us via email. Our team is standing by to help you figure out exactly which parts fit your vehicle!