Carbon Build Up (TSI / FSI Motors)

Do you have carbon build up in your Audi or VW? What causes it?

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Carbon build up is an issue with direct injection engines. On a direct injection engine, the fuel injector is inside the cylinder which means the fuel is sprayed inside the cylinder and combusts there so as the intake air comes in, it flows directly over the back of the intake valve and there is nothing in there cleaning it off. This causes the carbon to build up on the back of the intake valve.


Why does this happen?

This happens because of the PCV system, the PCV system serves to take blow-by that comes past the piston during the combustion process and vents it out of the crankcase. Things such as oil vapors, fuel vapors and anything else that would be unburned during the combustion process. That will get routed from the crankcase, out to the intake manifold. As all of these vapors reach the intake manifold, they leave deposits along the way, mainly on the valves because that is the most restrictive point.


What are the symptoms of carbon build up?

Most carbon build up issues happen in high mileage cars. For example, if you are over 60,000 miles and have never checked or clean the carbon build up, then you may be seeing some of these symptoms.

  • If your fuel mileage how decreased over the past year it could be a sign of carbon build up as it will restrict the airways causing you to get poor gas mileage
  • Misfires at idle due to insufficient air flow during a cold startup
  • The car may not pull like it used to due to an incorrect mixture of air and fuel to the motor due to clogged airways




How to check and clean carbon build up?

All cleaning methods require the removal of the intake manifold, however, you do not need to remove the valves to do so.

  • Option 1 – take a chemical and soak it on the valves then clean it by hand with picks and scrapers.
  • Option 2 – soda blasting, it is a great solution and will clean them very well but it makes a mess
  • Option 3 – walnut blasting, similar to soda blasting, this takes crushed up walnut shells to clean the valves

*Soda and walnut blasting do not require the removal of the valves themselves for cleaning




How can I prevent carbon build up?

A catch can is the most popular way to prevent carbon build up. What is does, is it takes your PCV system and reroutes the air flow so that it goes through a condensing can before it goes into the engine. Inside the can, it condenses all the gases, the heavy stuff goes to the bottom. You can then drain your catch can every so often and see how much build up that as been stopped by the can. This solution will help slow down the process but will not rid you of carbon build up.


Find a Catch can for your MK5 GTI here!

Also have Catch Cans for your MK6 GTI and Golf R here!


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