I have a 1997 Ford Ranger with a 4.0 ltr V-6 engine the engine runs rough and the chk. eng. light is on, I took the vehicle to a shop and they told me it was a leaky lower intake manifold, I want to know how I can test for a leaky intake manifold externally and internally?

On some early model Fords require programming of the electrical parts. If I'm not mistaken, There is an electrical connector that plugs into the EGR. You can call the local Ford dealership and ask about it but I'm pretty sure that's what needs to be done. Had an early model Ford Ranger come into the shop work in and found that out the hard way. I hope this helps you on getting correction for the problem at hand. Have a great wknd. Jesus loves you, John 3:16-17 (KJV)

Key on engine off, my info says, 35--45 psi.

has the cataletic converter been punched out to make it more like a resignator?

check engine light flashing or on means your vehicle is telling you hey somethings wrong you can have code pulled for free at parts store they will tell you what code means

You shouldn't have taken the car back,nor should the shop given you the vehicle,if you were willing to have it properly repaired.
The MIL Light is an indication of an issue or two and you said it runs rough and has no power. What more does a shop need. Repair it.

Is the Fuel Filter fairly new
Did they Clean the MAF Sensor,and make sure your air filter cover is on correctly,and you have no vacuum leaks.
They can look at all sensor data and resolve this ,if they wanted to.

Your mechanic did a good test by externally adding more fuel to the engine. The fact that the addition of the extra fuel to the engine changed the engines behavior would suggest he is on the right track.

try looking on the manifold

The water is from the thermostat housing, fairly common leak. The ticking maybe from the timing chain cassette. You may have already had the cam timing slip (the cam gears are not keyed, they are held in place by torque alone. The oil gauge sounds like an electrical problem (either sender or sender wiring).

1991-1994 2.9L and 3.0L Engines Firing Order 1-4-2-5-3-6 1995 And Later 3.0L V-6 With DIS Ignition System Firing Order 1-4-2-5-3-6
4.0L Engines Firing Order: 1-4-2-5-3-6 DIS Ignition System

I can tell you for sure that all US models of the Ford Ranger came with a emission system that incorporated a MIL or check eng light, go to the dealer and have them run your VIN on the Ford on line information service, that will give you the engine Calibration of the emission system, you can then find out what emission system was used, export or US.