I own a 1993 loyale and I recently swapped out my 93 loyale engine with a 1990 loyale engine and everything mounted up great. After mounting it up and getting it all running good, I noticed two things that are a little frustrating. 1st-I noticed my oil light coming on when I give it gas in the first 3 gears. I have done the obvious in checking the oil level, which is full since I filled it after putting the new engine in. 2nd, the 4wd button wont work and will not engage. I am wondering if both of these problems are due to wiring differences of the years. I tried putting the old oil pressure gauge (from the 1993) in to see if it would work, and still had the same problem. Prior to switching out the engines, I had no problems with either one of these two issues in both cars. Any ideas, thoughts, info, would be much appreciated. 

I have swapped engines around from 86 through 93. Have not seen that sort of thing. Some swaps I had to move the engine harness due to the connectors to the body harness being different, or carb vs spfi. On my 93 I replaced the instrument cluster to add oil pressure and volt meter, and found no wiring changes needed in the harnesses. Obviously, I changed out the sender.

Which oil sending unit is on the "donor" engine?

Dash light sending unit is small, pressure gauge sending unit is "Big".

Both use the same pins in the "engine to body" harness.

 

4WD shifting issue may be due to a vacuum hose not connected or split. Possibly a split/cracked line caused during the engine swap. 

Thank you guys, I'll definitely take a look at those things. The oil sending unit that is on the donor engine is the one from the 93 ("non donor"). I tried both and they both seem to be doing the same thing. 

So we fixed the oil light and it was just a bad connection on it. Still can't figure out why the 4wd isn't working. Everything is connected and in order on it. Any other ideas I should look at to get the 4wd working?

Check your vacuum lines for your pushbutton 4wd. Then check all the linkages for rust, being bent, ect.   I had similar problems, ended up drilling a hole in the trans tunnel and installing my own manual shift lever.