There are no "pipes" but vacum lines. However there are a few so more details of the one you are talking about is needed.
could be the
It is called the intake manifold.
replace the water heater inlet pipe on the intake manifold on a 3800
It is the metal pipe that runs down both sides of the intake manifold.It is the metal pipe that runs down both sides of the intake manifold.
Intake manifold delivers the fuel air mixture to the cylinder heads, exhaust manifold collects the gases after combustion, and channels them into the exhaust pipe.
What's under the intake is not a hose, it's a pipe which a hose attaches to behind the intake manifold near the firewall. If the hose is leaking, it's a relatively easy task to replace it. If the pipe is leaking, you will have to remove the intake manifold which is not an easy task (minimum 6 hours to remove and replace the manifold!)
exaust gases
the intake is the only way.
In a housing at the front of the intake manifold . Just follow your top radiator hose from the rad , it connects to a metal pipe , and the pipe connects to the housing for the thermostat at the front of the intake manifold. (Helpfull)
Just below throttle body, it fits onto a breather pipe runs from the valve cover routing under the intake manifold. A small pipe connects the pcv to the intake manifold
If you cant find it underneath on the chassis it's located under the intake manifold,you will see a petrol pipe connected to it,just look between the manifolds pipes
On the 4.0 L OHV engine follow your top radiator hose from the radiator , it connects to a metal pipe , the metal pipe is connected to the thermostat housing that bolts to the front of the intake manifold. Your thermostat is inside the thermostat housing
Faulty intake manifold gasket or faulty head gasket.