91 TT timing issue posted by AlexcamposZ32 on March 10, 2020 at 10:38 AM
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How do you know it is at 25 deg? from the data scan? That is probably the ECU adjusted timing. 15 deg BTDC timing is the mechanical timing of the engine, you need a timing light and physically measure that. When the issue happens, do a power balance test to isolate the cylinder. Start by checking all the electrical connectors for corrosion.