My check engine comes on w/ a knock sensor fault. Both Ping sensors were changed, and I still get this check fault problem. Questions: 1) What are possible causes of this fault? 2) What are possible cures for this fault? 3) Is/Are there any type of additive that can be administered, ie. engine oil treatments, synthetic oil (I am currently running 20/50 non-synthetic oil currently), NOS Octane Booster, or other octane treatments?