exaust gases
remove intake manifold.
It's underneathe the intake manifold, so yes it has to come off first. Not very fun.
Take off the cylinder head and make life easier.
Under the water neck, where the upper radiator hose to connected to the intake manifold on top of the engine.
on the exhaust manifold.
I found it on 91 V6 under air cleaner on front of the intake manifold. look around the upper radiator hose
Its under the intake
Under the intake mannifold (you have to remove it to get to it).
http://isuzufaq.ibctech.ca/#faq5
The oxigen sensor can be found on the exhaust manifold or exhaust pipe
Isuzu Trooper was created in 1981.
The intake manifold, exhaust manifold, and head must be removed. This is a major repair. On a 26 year old vehicle you might as well do a complete engine rebuild once you remove the head. The vehicle may not be worth the cost of the repair.