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Re: MPG readout- how accurate? Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Thu, 3 Feb 2005 05:37:43
In Reply to: MPG readout- how accurate?, rob 94 cse, Wed, 2 Feb 2005 17:22:31 Members do not see ads below this line. - Help Keep This Site Online - Signup |
MPG is simply fuel used and miles traveled. The engine control will adjust fuel flow to compensate for engine condition, air temperature, and driving style.
The engine control computer determines how much fuel goes into the cylinders by timing the opening and closing of the fuel injectors. Therefore, it knows how much fuel is going into the engine with time. That's fuel used. It sends that signal to the EDU, which also knows miles traveled. The result is simple arithmetic.
How accurate? Depends on the car. I've had some that were pretty darn good. I've got another that is about 20% optimistic. Remember a few things - the instantaneous readout is fun, but isn't correct. The long term one uses an average going back quite a ways, time/miles wise. If you haven't reset it in a while, it reflects the average across quite a few tanks, not the tank you're on now.
Octane rating has minimal effect on gas mileage. In fact, 87 could have slightly higher mileage than 93. Depends. Lower octane fuel actually has slightly higher energy content. Not enough to matter, but there is a difference, nevertheless. The engine control will adjust boost based on engine knock, which is partially related to octane. If your engine knocks on 87, it'll cut back boost. Less boost, less fuel flow. So it'll actually save gas somewhat. If you've got 93 and get full boost, you can get hooked on the boost and drive the car harder, using more fuel. Lower mileage with higher octane.
Some engines will make full boost on 87; some need 93. Depends on the individual engine, and even on the time of year.
posted by 192.249....
, Thu, 3 Feb 2005 09:06:02
, Fri, 4 Feb 2005 21:14:47, Thu, 3 Feb 2005 05:37:43 <-- Viewing This Message
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