Tuning tools - Vag-com and your Jetta/GTI/A3 2.0T FSI

Vag-com is a Windows based diagnostic tool for VW/Audi/Seat/Skoda vehicles. Interfaces that end in the word "CAN", such as the HEX-USB+CAN interface, are fully direct CAN bus compliant on new VW/Audi vehicles with the new 2.0T FSI engine.

Data blocks are used to report information from factory sensors and other interpreted data. These data blocks can be accessed and logged. From the data gathered, graphs can be made and compared. This is very useful to track the progress of performance modifications to your car, or to help diagnose problems that may arise.

Let's look at some specific data blocks and their interpretations. If you have a CAN based Vag-com, you can access these measuring blocks under 01 Engine, Measuring Blocks. Simply log the blocks that you are interested in, and start making graphs and comparisons. Let's go over some of the more popular blocks:

Label File Sample, your car might be different, but this will show all the blocks for reference.

  • Air Fuel Ratio - Block 031
    This block will log the air/fuel ratio as a lambda value off of the front factory wideband O2 sensor. To convert the value, multiply it by 14.7 to get your real AFR.

  • Fuel Rail Pressure - Block 140, 205 or 230 (check your label file)
    The 2.0T FSI engine uses a very high pressure rail for fuel injection into the combustion chamber. Some people have shown that fuel pressure will drop at high rpms or high loads. Usually a bad condition is if the rail pressure dives down below 100 bar in the upper rpms.

    A lot of people are getting a soft limp mode on this engine while chipped. Log your requested vs actual rail pressure, and look for large differences. This can set a limp (no boost) condition that will not log a CEL or set a soft code. Be careful, as the problem might not be the rail, rather this difference could be the result of another problem.

  • Projected EGT's - Block 112
    Projected EGT's, as reported by the O2 sensor in Celsius.

  • Boost Pressure - Block 115
    This block will show your absolute boost pressure. You need to derive atmospheric pressure to see what it really would look like on a boost gauge. Turn the car on, but don't start it. See what the value of this block is, this is your atmospheric pressure. To convert the value after logging use ((logged value - atmospheric pressure) * .0145) This will give you psi that you would normally see on a boost gauge.

  • Timing Correction Factor - Block 020
    Be careful with this. High CF's are not necessarily bad. These are the amounts of timing pull in each cylinder. It can help with tuning, but realize that your ecu is very advanced and high CF's don't mean that there is an immediate problem.

  • Timing - Block 011
    This is good to log as you make changes to the system, or to keep an eye on as you get new ecu flashes or other mods. This is the real curve behind Block 20.

  • MAF - Block 002
    Read the grams/s of air going into the engine. Keep an eye on this when making changes to your car. More air, means more power. Useful if you have, say a new air filter or a new exhaust. Remember to look at the complete picture though.

  • Intake Air Temp - Block 006
    This one is obvious on a turbo car.

  • Vag-com Dyno - Block 120
    Log the engine values for load and use Andy's Butt-Dyno spreadsheet to create neat graphs. Great for comparisons after modifications to your car.
Vag-com block 120 dyno graph

Vag-com can be a valuable tool if you have a VW/Audi 2.0T FSI engine. Whether you just need to scan for occasional codes, modify your long coding, or want to track performance and modifications, Vag-com is the only tool that can do it all.

Posted in Submitted by deviantspeed on Wed, 2006-12-27 16:22.
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Invaluable FSI information. Thanks for the writeup!


Deviant Guest (not verified) | Fri, 2006-12-29 13:43

Great information, keep up the good work.

Zack (not verified) | Thu, 2006-12-28 20:11

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