Our “Read & Repair” series gives you background information about a particular part as well as tips to help with the job. Today’s topic is DISA valves.
What is a DISA Valve?
It isn’t something on your diesel, nor is it a component for your sink! It’s a component used on various BMW engine platforms from 2001-2012 to control the length of the intake manifold runner.
What Does DISA Mean?
DISA stands for Differentiated Intake System Actuator, or if you’re up to date on your German, you may call it “Differenzierte Sauganlage”. If you’re familiar with domestic vehicle operations, you may know it as Intake Manifold Runner Control. Ford has used it in many of their popular V-6 and V-8 engines for years. GM and Chrysler also have their own versions. The DISA system is BMW’s version of IMRC.
How Does the DISA System Work?
When an engine’s intake valve is open, atmospheric pressure forces air into the low-pressure area inside the cylinder. When the intake valve closes, the air in the intake runner that’s moving rapidly toward the cylinder slams to a stop and stacks up on itself, forming an area of high pressure. This high-pressure wave makes its way up the intake runner away from the cylinder. When it reaches the end of the intake runner, the pressure wave bounces back down the intake runner.
If the intake runner is just the right length, the pressure wave will arrive back at the intake valve just as it opens for the next cycle. The extra pressure helps force more air-fuel mix into the cylinder. The problem with this technique is that it only provides a benefit in a relatively narrow rpm range.
To improve power and efficiency, it is also beneficial to have the intake air moving as fast as possible into the cylinders. Doing so will increase turbulence and better mix the fuel with the air. One way to increase air velocity is to use a smaller diameter intake runner. Think about it. The volume of air entering the cylinder each cycle is roughly the same. If that volume of air runs through a smaller diameter pipe, it will have to move faster.
There’s a downside to using a smaller diameter intake runner, though. At high engine speeds, when a lot of air is moving through the pipes, the restriction from the smaller diameter may inhibit airflow. For large airflows at higher speeds, it is better to have large diameter pipes.
For the best of both worlds, manufacturers such as BMW now use dual intake runners for each cylinder, one with a small diameter and one with a large diameter, or varied lengths. They use a butterfly valve to close off the large diameter runner at lower engine speeds when the narrow runner can help performance. At higher engine speeds, the butterfly valve opens to reduce the intake restriction, increasing the top-end power output. At the end of the day, what you need to know about DISA systems is that they use long intake passages at low rpm and short passages at high rpm.
"At the end of the day, what you need to know about DISA systems is that they use long intake passages at low rpm and short passages at high rpm."
What’s a Common Cause of Failure?
When a BMW DISA valve breaks, one of the first concerns a customer may have is a knocking noise coming from the engine compartment. The noise is the sound of the DISA valve flap freely spinning on the broken plastic shaft.
What Causes the DISA Valve to Break?
Over time, carbon builds up in the intake manifold. When it builds up on the DISA valve, it can prohibit the flap from closing and opening fully, causing either the plastic flap or the plastic shaft to break.
In some cases, the customer may have concerns of rough idle, lack of power, illuminated Check Engine Light, or vehicle hesitation. All of those concerns are the result of the flap either moving back-and-forth or being stuck in the incorrect position. In either case, the DISA Valve is broken and needs to be fixed.
What’s the Best Solution for a Broken DISA Valve?
In the OE world, the only option is to replace the entire DISA unit. Now, if the housing is damaged and the vacuum is leaking, a full replacement is required. But for most DISA-related problems, all that’s needed is a repair kit such as TechSmart’s DISA Valve Repair Kits. These kits come complete with everything a technician needs to repair only the unit rather than replace the entire thing, which can save customers a lot of money.
Two Tips to Remember for DISA Valve Repairs
Once the new components are installed on the DISA Valve, use caution to install it, and make sure the vacuum lines and electrical connector are connected. If any trouble codes were stored or any drivability concerns are noticed, the stored memory should be cleared before verifying that the repair is complete and the problem is corrected.
|Ryan Kooiman is the Director of Training at Standard Motor Products. In addition to leading SMP's award-winning PTS training program, he is the face of SMP's 'Installation Spotlight' videos on YouTube. He has ASE Master L1, L2, and L3 Certifications, and has had articles published in over 30 periodicals.|