my motor is knocking on 2000 Ford Excursion

at first it started off light now there is a heavy all starteed when i put a low grade of gas in it. i ran all that gas out and put premium in it with some lucas octane booster and it still knock bad can any one help me

by in Valdosta, GA on January 15, 2011
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2 answers
ANSWER by , January 15, 2011
This year and model V10 has been a charcteristic issue of having spark knock, but you stated "heavy knocking". Are you sure that it is spark knock (pre-detonation or pinging) not an oil pressure issue? The mass air flow sensor could be running it lean, a scan tool would be able to monitor the fuel trims to know for sure. Have you switched grades or brands of oil? For some reason, my truck responds to the factory recommended oils (5w-30) in reducing spark knock. I am not entirely sure why though. A can of combustion cleaner may also be in store for you. You might have excessive buildup on top of your pistons increasing the compression ratio higher than desired. I
ANSWER by , January 15, 2011
If its a real loud knock , it sounds more like a bearing on the crankshaft or piston has gone bad, not caused by cheap gas. If its a bearing, it will get knoch with the rev's of the engine and never go away. Take it to a cheap shop to run a diagnostic.. maybe $35.00 to $50.00 I cant tell unless i heard it.