Carbon Removal FSI and TFSI Engines

Getting to grips with Carbon Removal FSI and TFSI Engines looking at the symptoms that can occur.

About Carbon Build up

Carbon is a bi-product of combustion. Think of when baking a cake, you have all of your ingredients ready. In our case in a car they are air (Nitrogen (N2), Oxygen (O2), Carbon Dioxide (CO2), Water (H2O)). Fuel (Hydrogen and Carbon (CnH2n+2)). On there own mixed up you would end up with soup, Similar to the dough before baking.

Heat is the key into turning our soup into something useable. In turn using heat will deconstruct and reconstruct ingredients differently thus creating different chemicals. What goes in has to come out, albeit in a different form. From all the chemical elements above, the amount carbon locked up in each chemical is quite big. Therefore if the heating process isn’t quite right, the result is a very different chemical output. Ending us up with a very funny looking and funky tasting cake.

The difference in the combustion process is what can cause excessive soot or carbon. What can cause this difference?

• Fuel quality may vary from station to station
• Fuel has different ratings (Make sure your using the correct one for your vehicle)
• The vehicles engine or components may have an underlying issue
• The vehicles engine ECU may have software or hardware issues

As you can see there is no easy fix without a bit of detective work. With common consensus is “oh its a FSI or  TFSI engine this is common”. Wrong!. Carbon build up is common however in theory its not meant to happen. The reasons for this is due to one or more of the bullet pointed reasons above.

Common fault codes associated with carbon build up

On a Volkswagen, Audi Seat or Skoda vehicle you will not always see a fault code for Carbon build up FSI and TFSI Engines or any engine for a matter of fact. But common fault codes we do see are:

• P0300 Random/Multiple Cylinder Misfire Detected (16684 )
• P3138 Intake Manifold Runner Control – Regulation Deviation ( 19594 )
• P0401 Exhaust Gas Recirculation (EGR) System – Insufficient Flow Detected ( 16785 )

The Repair

On the vehicle we took photos of above, was an Audi A5 3.2 FSI, the customer complained of rough idle and hesitation very intermittently. We took a look at the vehicle.

Using ODIS the manufacture diagnosis machine, we pulled a few fault codes one relating to Random/Multiple Cylinder Misfire Detected, and one related to a misfire on cylinder 5 and 6 initially.

We recorded the codes, the vehicle when presented to us showed no symptoms. After extensive road-test we found it was misfiring. Using an oscilloscope we narrowed the fault down to an electrical fault, where the coil packs would loose their feed for a second or two then come back online. Following the harness back we found an ultrasonically welded crimp had made its way free held together only by the heat shrink, which after time would warm up and expand enough to allow the crimp to move apart.

This was the cause of the misfire and also due to the misfire, the poor combustion created excessive soot. Which in-turn was reintroduced into the engines intake and settled on the back of the inlet valves and the intake tract. We use a valve cleaning system called Tunap with the product (soft walnut shells) supplied from Volkswagen to carry out a complete intake Carbon Removal FSI and TFSI Engines. The fault we saw was not a result of carbon build up, but caused it.

Diesel powered engines are naturally sooty so this is a regular occurrence even if no fault is found within the vehicle. We always check beforehand to asses what fault may be manifesting.

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Like this topic then maybe you should read P0104 Exhaust Gas Recirculation

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