Ford Repair: 2000 Ford Ligtning, piston damage, ford lightning

Question
I just bought a 2000 ford lightning from an individual and he said he just rebuilt the motor about 10,000 miles ago. When I got it home it started chattering like a diseal and started losing oil pressure. I had to put 89 octain gas in it and it requires at least 91, will that make it chatter. What should I do. PLease email me back asap.

Answer
Adam-

  Yes, if the motor requires 91 octane gas, 89 octane can make it ping.  That's actually somewhat dangerous since that pinging is caused by detonation which can result in piston damage.  I don't think that would account for your loss in oil pressure, but anything's possible.  Hope this helps.

Steve