After installing a Taurs 2 speed fan in my 93 ZJ 4.0L, I thought it will be better to throw in a 136 amps alternator to help in compensating for current draw and keep enough voltages to other sys.
I did not see any changes in current boost, just like the old 90amps alt is still there, sometimes needl goes to near 9 volts when I switvhed to the high speed.
I just want to know how do I measure the alt in order to see if its 136 amps, or 90 amps.
I don't know what tools you have access to, but if you use an amp meter (the clamp type),and a battery tester you can find out. Take the amp tester and put it on the negative battery cable, then take the battery tester and put a load on the battery. You will then be able to see how many amps your alternator is kicking out, or if its working correctly.
Marcos is correct, the 136A ND from a V8 ZJ/WJ/Durango is physically larger than the 90A ND, and if you're replacing the 90A with the 136A unit, you'd have had to grind into the mounting by about 1/4" to clear the larger frame. So, chances are you still have the 90A.
It should also be borne in mind that the alternator cannot generate maximum output potential until the spindle speed is up around 3300-3500rpm - which comes out to about 1000-1200rpm at the crankshaft. If you're checking at idle, it's not a valid test. (i.e. - my 195A Delco CS-130 can only generate some 70A at idle. Period. At 1200rpm, it can generate 198A - solid!)
NB: The current function on the typical DMM (that you'd buy at the hardware store or parts house) is only good for about 10A before you blow the fuse. The "lobster claw" type - that clamps around the wire and reads from the magnetic field the current generates - can be good for up around 500A depending on the model. If you look at one, make sure it reads DC Amps (since AC and DC amps generate different magnetic fields, trying to read a DC field with an AC ammeter will confuse the meter and give you an invalid reading. And vice versa.)