The Importance of Carbon Cleaning Your Direct Inject Engine
The Importance of Carbon Cleaning Your Direct Inject Engine 11/08/17

Carbon Cleaning Your Direct Inject Engine -- Get Back Your Lost Performance!


I’m sure many of you know and have heard of the issues that come from Direct Inject engines. While there are many benefits, there are also some downfalls. Positives include better fuel economy, efficient power and tons of headroom if you enjoy modifying your car! The negatives are low speed pre-ignition (LSPI) in some models and what we will be addressing here, carbon build-up.



Carbon build-up is when carbon deposits are left on the back of your intake valves. In a typical port injected car the fuel injectors spray over the intake valves essentially cleaning them of any sort of carbon or debris. This keeps them clean for thousands and thousands of miles and all but eliminates the need for carbon cleaning. In a direct injected car, the fuel injectors spray directly into the cylinder head, bypassing the valves and thus never cleaning the back side of the intake valves. Due to no fuel flowing over the valves, carbon deposit can build up and cause many issues. In some cases you will notice drivability problems, power degradation, miss-fires, cold start issues and more.

The good news is at this can be remedied for a fair price if brought to a shop who is experienced with the platform. It is important that they have done this procedure before as if done wrong, can jeopardize your expensive engine! Some will ask, how would you clean the back of the valves if they are in the head? Well there are a few ways, but the most common and the way to do it is via walnut blasting. Walnut blasting is using a pressurized vacuum style machine used to spray crushed walnut shells over the back of the closed intake valves. Doing this allows for the walnut media to disrupt the carbon, removing it from the valve and intake chamber. The benefits are immediately noticeable and the procedure should last thousands of miles.

All vehicles that are Direct Injected without a supplemental port injection will suffer from this issue. Some are worse than others and require the service more frequently. Vehicles that are Direct Inject with a supplemental port injected setup should not need this service or at least not for a long time. On a standard Direct Inject engine, we recommend performing this service atleast every 50,000 miles. With hard usage or if you notice drivability issues or power loss, it may be worth considering doing it earlier. Direct injection is the wave of the future, but as with all new technology, there are some by-products which will need to be addressed.

Please check out the pictures below. These are from a 2015 Subaru WRX equipped with the FA20DIT engine. The vehicle was tuned by us from early on in its life. The customer brought it in for some additional modifications along with the carbon cleaning. He complained of some drivability issues he noticed got worse over time along with power degradation since the initial dyno session. Can you imagine how your valves look with higher miles? We offer this carbon cleaning service for any direct inject engine, so please reach out for a quote on your specific vehicle!




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  1. What would the cost be for a carbon cleaning plus dyno tune for a 2015 WRX with cobb intake and grimmspeed ebcs?

    Eric Peterson
    March 20, 2019 | 1:21 pm
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