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Old 04-28-2009, 03:47 PM   #8 (permalink)
Master EcoModder
Join Date: Aug 2008
Location: South Dakota
Posts: 460

WonderWagon - '94 Ford Escort LX
Last 3: 51.52 mpg (US)

DaBluOne - '99 Ford Escort SE
90 day: 48.97 mpg (US)

DaRedOne - '99 Ford Escort ZX2 Hot
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Originally Posted by Wonderboy View Post
Could you explain the risk of knock/ping involved with using regular octane gas? Should I consider using 91?
In the case of your '98 Civic EX, if pinging begins to occur it will immediately be detected by the anti-knock sensor (think they became common about same time as ODBII was introduced) and the ECU will automatically adjust ignition timing to avoid knock/ping. If that's the case you'd get somewhat better mpg with 91 octane, but whether the improvement would be justified by the increase in price is doubtful.
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