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Old 05-30-2011, 11:28 AM   #1
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The Mysterious Ultra High MPG 3.8 and GN too.

The last version of the "3.8," before the engine was called a "3800," came in at least 2 flavors: Ordinary and Legendary.

There was a 3.8 variant that got unspeakably high gas mileage. These cars were coveted by taxi companies. My friend who owns a taxi company bought his first one unknowing of any of this. The first day they put it in service, at the end of the day, the driver says, "It runs good but the gas gauge is broke." It barely moved after about 1/2 days use as a taxi. They got over 25-28 mpg in city use.

I even remember a road test of a GN or GNX where they were driving to the strip with the 5th wheel on and running and they were getting 44 mpg on the highway. I suspect this Mystery 3.8 might even appear in the turbo cars too. (Or will all turbo Buicks get 44 mpg on a level highway?)

We never figured out which 3.8's got the mileage. It was probably something like has to have the "brown" injectors instead of the "blue." And maybe a few more things.

Does anyone remember this or has identified that amazing variant?


Last edited by MrCreosote; 05-31-2011 at 01:24 PM.
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Old 08-22-2011, 07:08 AM   #2
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Re: The Mysterios Ultra High MPG 3.8 and GN too.

It may be legend, or it may be that the ECM was programmed a bit differently. From late 1985 on through at least 1994 the GM ECMs almost all had coding for Highway Fuel Mode and Highway Spark Mode operation. Even though the coding existed, it was turned off in the programming because the operation at 17:1 mixtures and 48 timing advance at light load values and low throttle angle would not allow the engines to control NOX emissions enough to meet EPA standards. Some of us who have played with the Highway Mode settings have been able to achieve more than 30 MPG highway on L98 V-8s and slightly better on LB9 V-8s in F-cars which were rated for 22 MPG.

GM pretty much had a method to increase mileage but at a cost of higher emissions of nitrides of oxygen. The result is that we burned 30% more fuel on the highway because Uncle Sam was more concerned about what it thought might be damaging the stratospheric ozone layer.
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