12/06/2026
Surgery carried out on a Mk6 GTI on the dyno..
Golf mk6 GTI 2.0TSI DSG came in for inlet cleaning, injector testing and to diagnose misfires and fuel trim issues, then hopefully a stage 1 tuning session.
All injectors came back from Callum at the Fuel Injector Clinic perfect, which resolved the misfire issues, but they didn't give any answers to the rich at idle fuel trim fault codes.
We initially couldn't see any issues with the fuel trims whilst on the ramps,, so we strapped it onto the dyno for a logging session and to get the engine up to working temperature and conditions.
All was good for 10 minutes, then we noticed the short term fuel trim would peg -27%, with the long term adaptation trims creeping up to -10% after 1 minute. But the short term trims under load whilst driving would drop to -7%.
Straight away we knew that the hpfp was leaking neat petrol directly into the oil, then the petrol vapours were being sucked into the engines combustion mixture via the pcv valve.
A quick test was to blank the pcv pipe going to the inlet manifold, this would cause the -26% fuel trim to drop to -7%.
Unfortunately TPS couldn't get a oe genuine fuel pump to us until the following day, which meant the customer went home at 125mph on train from Nuneaton.
Friday morning comes, we drained the contaminated oil petrol mix, fitted a brand new oe genuine hpfp and managed to get the car fully tuned up, making some epic stage 1 numbers. The only modification was a full custom cat back exhaust system.
So after 8 months of constant issues since he purchased the car, we managed to sort it out for him.
