I have a 92 Sentra with 126,000 miles. I just got the smog done on it, it passed the emissions part but it failed the "functional" part because the Ignition Timing is off. It says Fail: Ignition Timing 8 BTDC. I was wondering if anyone knows what it's supposed to be set at. Could I fix this problem myself or do I have to take it to a mechanic?