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Why Do Some 4.x Engines get 26+MPG, Others <18 MPG Highway

1461 Views 5 Replies 4 Participants Last post by  steelybill
My 87 Eldo (4.1, 63,000 miles) has gotten, at best, 22 MPG on the highway. Usually it is less than that. And I get 15-16MPG around town. I am light footed too.

I see many others posting 26-28 MPG highway, and 19-20 MPG city.

I have tried to check/replace everything I have heard about on this forum, yet my mileage has not improved, other than when I finally put good plug wires on (upped city from 13 to 16 MPG city).

Only thing I haven't done is replace the catalytic converter. How do I determine if it is restricting/clogged?

Any other suggestions?

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The list of factory equipment codes will show the final drive ratio.
For example, my old '85 has a listed code of F79, which is a 2.97:1 final drive ratio. They list 3.73, 2.93, 3.08, and 3.42 for this one. If the mileage has always been the same and not recently gone down, it may be the drive ratio and not some engine function.

Just an idea!!

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