Adjusting Injection Quantity with VAG-COM

Injection pump wear, fuel quality, tuning, nozzles, and a variety of other factors can change fueling levels in TDIs. This can cause smoking, slowdown shudder, or low power.

Changing Injection Quantity (IQ) is easy. Here’s how to do it.

Cable/Software/Port Setup

This how-to assumes that you’ve got your VAG-COM, downloaded the software, and made sure your car can connect to your computer. If you haven’t done this yet, www.ross-tech.com has detailed instructions.

Checking and Changing IQ

You car has to be running to get an accurate injection quantity reading. And it has to be up to operating temperature. So it’s best to drive the car for 20 minutes or so, some of it at highway speeds, to make sure you’ll get a good reading. You should not run your A/C during this test, as it will affect readings.

The screen prints in this article are from a 1997 VW Jetta TDI. If you have a different TDI some of the data displayed may be slightly different, so keep that in mind as you proceed.

You’ll first see this screen:

This is where VAG-COM launches. Click on the button named Select under the the words “Select Control Module.” Next you’ll see this screen:

All the engine control modules are listed, even if your car doesn’t have some of them, such as ABS. Click on 01-Engine to proceed and you’ll see something like the following screen:

The engine data will take a moment to populate. Newer cars populate faster than older ones (slower ECUs). Once the screen is populated, you can click on Login-11 to first login:

Type the numbers 12233 into the box to the right of the words Enter Code and click on Do It! This will take you back to the Engine screen:

This time click on the button Adaptation – 10. Next the screen below will appear:

However, you’ll see channel 00. Click the Up button to Channel 01 and you’ll see Adaptation numbers.

At the top of the screen you’ll see RPM and Injection Quantity. The IQ will most likely be a number between 1.0 and 3.0.

Next, look at the numbers on the left side of the screen. Below the Channel window you’ll see two boxes, one titled Stored Value and the other titled New Value. The default stored value is 32768. If your IQ has been previously adjusted you may see a different number. There’s a limit on the number range for IQ, it varies by ECU, but is approximately between 32645 and 32786.

The IQ measurement numbers are slightly counter-intuitive. A higher Injection Quantity (such as 3.0), will flow less fuel than a lower quantity (such as 2.0). And a lower new value (such as 32725 instead of the default 32768) will flow less fuel than a higher new value.

Why change Injection Quantity?

If your car:

• Smokes more than you want
• Shudders at slow down or idle

You may want to reduce fueling (increase the IQ number)

If your car is low on power, you may want to increase the IQ number.

Changing IQ

Here’s how to do it. On the adaptation screen, shown below:

Click into the New Value box and type in a new number. If the stored value is 32768 and you want to reduce fueling, try a lower number such as 32750 or 32725. Click on Test at the bottom of the screen. The IQ number will change (and your engine tone will change, too). Look at the new Injection Quantity at the top of the screen and see if it’s what you want. You can further adjust the IQ by typing in a new number and clicking on Test, or by using the up and down buttons to the right of the New Value box.

Once you’re satisfied with the IQ and want to test drive the car to gauge results, click on Save at the bottom of the screen:

You’ll be asked, Are You SURE?

Click on Yes to save the new setting. If you want, you can drive the car with the computer hooked up to determine if you’ve achieved the result you were after (more power, less shudder), and further adjust the IQ if needed.

Once you’re satisfied, click on Done, Go Back at the bottom of the screen, Back on the engine screen, and Exit on the main screen to exit VAG-COM.

Done!