In this world of increasing electronic gadjets and gizmos, some down to basic mechanical principles are to be observed. No amount of manipulation with the ECU mapping of ignition or fuel injection can compensate for weak compression, leading to power loss, high fuel consumption.
a. Incorrect valve clearance - need to re-adjust valve clearance for non-hydraulic valve actuating mechanisms. Most cars nowadays uses shims, and great skills is required, including the ability to read the micrometer.