Although this method is more common with software coders, the same principle can be applied to automotive troubleshooting.
In coding you read off the code line by line, explaining what the code is doing to the duck. Stepping through how it works shows you possibilities of failure or mistakes, explaining it also helps you understand it better. The way this works for automotive is you have your rubber ducky or any thing really, your favorite 10mm socket perhaps and you explain to it step by step how the thing works that isn’t working. Walking through the order of operations makes you think more about what its supposed to be doing and hopefully reveal what of those steps could be failing to cause your problem you are seeing.
For example I have a boost leak lets say. Everyones first thought is probably the diverter valve, which very well may be the problem as it is a more common failure point. But lets do a high level overview of the boost system.
- Cold air comes in from the intake to the turbos compressor.
- The compressor pressurizes and heats up the incoming air
- Diverter valve holds compression to a point and blows it out again.
- Hot, compressed air from the compressor passes through pipes to the intercooler, which cools it down.
- Cooled, compressed air enters the cylinder’s. The extra oxygen helps to burn fuel in the cylinder at a faster rate.
- Waste gas from the cylinder exits through the exhaust outlet.
The hot exhaust gases blowing past the turbine fan make it rotate at high speed. The spinning turbine is mounted on the same shaft as the compressor
- The exhaust gas leaves the car
So from this we can see a few more things other than the diverter valve may be involved. The pressurized portions of this is also where we need to look. The turbo would like be making a racket if it was a problem. The charge pipe/turbo outlet pipe could be blown off on one of its ends and need to be re-attached, intercooler itself is probably fine if it hasn’t taken any hits, pipes will blow before it does. Same goes with the cylinders, you likely will be seeing much more of a problem if they were to blame than a boost leak.
So what we came up with is the piping and diverter valve that need to be checked. A quick visual for blown off pipes followed by smoke check would likely be the best way to test this.
So its a little more complex than exhaust gases go into the turbocharge and spin it, witchcraft happens and you go faster. You need to have a decent understanding how how your engine works to troubleshoot this way.