bad wiring connections and earth connections often are masked by changing the ignition amp, which often may not be the true fault. This is especially true on 4x4 - in which case check the 3 connectors across the bulkhead above the camcover, especially the righthand one with the large wires. Disconnect them and check cleanliness of the connections. Check the connections also round the ignition amp and coil.

Also check (preferably unbolt, clean and replace) the loom earth connections on the inlet plenum and the large battery to chassis connection on the front edge of the battery tray.