Removing the front exhaust pipe from the engine will give you the necessary space to replace the starter motor on your Isuzu Trooper. If you decide to unbolt the exhaust pipe, unplug the Heated Oxygen (HO2S) sensor connector-threaded on the pipe-and negative terminal from the battery first; then proceed to remove the starter as indicated here. Or follow these steps as an alternative procedure.
Park your car in a safe place with a level surface and open the hood. Disconnect the black, negative battery cable.
Raise the front of the vehicle using a floor jack and safely support it on 2 jack stands.
Remove the starter motor heat shield from underneath the vehicle (driver side) using a wrench or ratchet and socket.