I have a 1995 jeep wrangler rio grande with a 2.5 4 cylinder engine that has blown up, I found a 1991 engine from a junk yard, will it fit in my 1995 model.

SOURCE: engine code 95 jeep grand cherokee lerado

12 is a battery disconnect within the last 50 start cycles and 55 means the end of the diagnostic cycle.  Basically the computer found nothing wrong. The 12 code may seem incorrect if you haven't disconnected the battery recently, but from my experience the 12 code shows up almost all the time regardless.

SOURCE: 4wd problem jeep wrangler yj 1995

i just bought a used 97 CHEROKEE but i had the same problem, when i got to looking at it i found out the front driveshaft was shot, look at that, if its not it i would say its probably the transfer case especially with an older vehicle like that which is a very expenxive repair

SOURCE: serpintine belt

This link will take you to a picture of the diagram. If the link doesn't work contact me and I can email you the picture directly.

http://autorepair.about.com/library/illustrations/bl506a-lib.htm

SOURCE: location/testing of crank sensor 1995 jeep wrangler

Should be on the bellhousing on the drivers side just where you need rubber arms to reach it.Should have no continuity between b&c terminals (check with ohmeter) Harness plug is usually on the drivers side between the master cyl and the back of the engine (unless someone moved it)

SOURCE: 1995 Jeep Wrangler 2.5L Fuel Pump/Check engine light

Could be one of several items...I'd check the fuel pump relay, auto shutdown relay and the ignition switch itself. I'd bet on it being one of those relays but, we all have been fooled at least once!!! I'd also make sure that body and engine grounding is good and clean. Relays can't work properly without a good ground.