Why does Golf gti mark 4 16 valve only start on 3 pistons not 4?

to save on gas only three pistons are needed to start the engine properly I would say you have faulty sparkplug wires and when the engine warms up the fourth will kick in or you have a faulty plug...good luck

This is a common early warning sign of cylinder head gasket failure, especially where the gasket is failing between a waterway and a cylinder bore. Coolant can find its way into the cylinder bore due to the fact the cooling system is pressurised, and this will inhibit formation of a spark until the engine has warmed up sufficiently to drive any moisture from the cylinder.

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