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

1462 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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Oxygen sensor......that is supposed to be replaced every 30k miles on that engine. MAP sensor also has a lot to do with mileage. BTW: any E codes?
Replaced Oxygen sensor recently
AC Delco Plugs
Accel wires: the large ones 8 or 9 mm
Drive at 60 mph on highway with a light foot
Stock 205 tires slightly overinflated

Only code is related to EGR: PO48 Current/ EGR Fault

I replaced the EGR, cleaned the passages. I get the check engine light after running the car for about 20 minutes.

This was discussed here:

Not sure what to try next.
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