96 escort gt

I have been looking for a new or used 1.8 eng. I have been told by all that my scort will only except a "96" eng. They say it's a 96 only car but 91 thru 95 are the same and they can't tell me why. I thought all 1.8L were the same. Can someone tell me what is different on 96's. I also have a 92gt with 167,000 and runs great. I have never had any problems with it. So i bought the 96. The motor has a knock in it now after i had it for 6000 miles. It now has 96000 miles. I know the car was well cared for so i am thinking there was a problem with the 96 1.8L. Any thoughts or info will be welcome. Thanks Jay