In a method and an arrangement for determining a fuel quality of a fuel for a combustion engine fuel is conveyed from a low pressure fuel tank to a high-pressure volume, and injected into at least one cylinder of the combustion engine. A control valve is provided for controlling directly or indirectly the amount of fuel injected into the at least one cylinder. An actual value of a timing signal of the control valve is compared to a reference value of the timing signal of the control valve and a fuel quality parameter is derived from a difference between the actual value and the reference value of the timing signal of the control valve and/or that a fuel quality parameter is derived from a gradient of the pressure increase during a build-up phase of the pressure in the high-pressure volume compared to a reference value of the gradient of the pressure increase in the high-pressure volume.