I have a problem that no one locally has been able to help me with. If you have time I would greatly appreciate any suggestions you have.
I bought a 1998 Honda Civic HX Auto CVT for gas mileage, I drive 4,000 miles per month. I have been unable to get more than 30 MPG highway (80 MPH). The car came with a CAI and 2" exhaust, no resonator, cheap aftermarket muffler. I had the timing belt/water pump replaced, fuel filter, plugs, plug wires, distributor/ rotor and Primary 02 sensor. I also cleaned out the EGR ports that were completely clogged. When the 02 sensor was replaced a crack in the exhaust manifold was discovered and a header was put on. The car is also currently without a cat. The gas mileage has not changed for the better following and of these events. I have a scan gauge. The MAP runs around 11 at 80 MPH 3400 RPM. A friend looked at the fuel injectors when the EGR system was replaced and said they looked to be in very good condition. I should also mention the car burns about 1qt of oil every 1000 miles. The PCV was replaced also. I am currently running 15w40 mobile one synthetic oil. I am basically out of options. I am considering putting on a fuel pressure regulator, thinking that the ECM may not be able to adjust for the increased air intake but have no other ideas. I read that the lean burn engine can run as high as 19:1. I believe the car should be getting 38 to 42 MPG on the highway. I got 27 today with the A/C on. The car also has new tires/ alignment. I've also adjusted the timing from 10 to 14. The Honda repair manual states 12 +-2. This had little affect. I should also mention that the car rarely runs in closed loop at speeds over 70MPH. I have a V8 Lincoln LS that gets 24 on the highway. This civic mileage really stinks. I should also mention that I am only concerned at fuel economy and performance is of no concern. Any ideas?

 

I've 2000 HX with 5w30 oil, that's what the manual suggest and it should improve the MPG, I got about 36 MPG in 80 MPH 75% highway, I used get 40 or above MPG when it run 45-60 MPH in most "nice street" in city (not much red lights though). Also, depends on how "light" accelerated you change each gear, I used be light accelerate to a minmun level for each shift, ex: 45 MPH change from 4 to 5 speed. But the start up speed is very slow compare to other cars next/behind of me. Your is CVT the MPG should be lower than 5 speed.