Usefulness of Engine Logging

Myth: My engine is already in good condition so I will not benefit from logging

Fact: Logging still comes in handy for preventative maintenance. Here is an example of bad fuel timing that goes unnoticed in virtually all cases. The following charts show before/after fuel timing adjustment.

Bad Fuel Timing

4.6 7.5 10.5 13.5 16.5 19.4 10001400180022002600300034003800 RPM °BTDC
Requested Actual

Good Fuel Timing

5.7 8.4 11.1 13.9 16.6 19.3 10001400180022002600300034003800 RPM °BTDC
Requested Actual

The fuel timing issue tends to deteriorate gradually (possibly over the course of several months) and drivers will not notice until the problem becomes severe. By logging we can do preventative maintenance at once. Optimal fuel timing contributes to better power and reduced emissions. A similar case applies to the MAF sensor, which is another common deteriorating item in some engines. It slowly reduces power until it becomes weak enough for the driver to finally decide that something is wrong. This could be prevented early by logging. Logging also assists in fine-tuning boost control and other engine parameters during custom tuning.

Diagnostics

Here is a real-life diagnosis & solution of a stock car BEFORE tuning. Without logging, these charts and diagnosis would not have been possible.

Serious Overboost Diagnosed

0 5.1 10.3 15.4 20.5 25.6 10001400180022002600300034003800 RPM PSI
Requested Actual
We found overboost in logs that the customer was not aware of. Adding performance with any tune or product will result in even more severe overboost, causing early turbo failure. The customer replaced the factory boost controller and boost hoses, which are normal wear items. See the next chart:

N75 Valve and Boost Lines Replaced

0 4.5 8.9 13.4 17.8 22.3 10001400180022002600300034003800 RPM PSI
Requested Actual
There’s an apparent improvement, but it’s still overboosting. Engine logs revealed that the N75 duty cycle was a lot higher than normal so the turbo actuator was adjusted to factory specs. See the next chart for the result. His turbo was a 6-month old factory replacement with an incorrectly set actuator!

VNT Actuator Adjusted

0 3.3 6.7 10 13.3 16.7 10001400180022002600300034003800 RPM PSI
Requested Actual
Now his engine is optimized for longer turbo life and it’s ready for a great tune. If minor overboost or underboost persists, they may be corrected in a custom tune.



What tool is used for logging?

VCDS from Ross-Tech is the most popular tool for Volkswagen, Audi, and Porsche engines. Currently we are a Ross-Tech dealer. If you would like to buy this cable through us, please contact us for more information.

Do you have a logging guide?

Our logging guide can be found here.