I have a 2001 Civic EX 1.7L the problem I am having is in the last year my fuel economy has went from 28mpg to 22mpg this is general driving hyway and in town. Bought this civic a about three years ago with 175,000 miles and now my civic now has 200,000 miles. I did just replace the head gasket in the last year. I did replace the thermostat with a 170 deg one after reading this fourm I see the engine needs to run a little hotter for economy. What thermostat temp would be good?. It does at times hesitate when I first start it up cold and just start to accelerate after that it runs good. I have replaced the forward O2 sensor a few months ago as it gave a trouble code i thought this was the cause of the hesitation but it still does it. I have not had any trouble codes come up when it hesitates. Just replaced spark plugs and installed new paper air filter removed my K&N to see if it might be that. Checked compression it's running 190 across all four. Is there a fuel filter I can change for I cant seem to see one in the service manual? Is there a way to check and adjust timing on this engine?

 

your fuel filter is in the tank.. it attached to you fuel pump/gauge sending unit.

 

Make sure the cam timing is correct (setting of the timing belt). Spark timing is not adjustable, it is determined by the crank position sensor. Use stock thermostat temperature only. If the ECT sensor is out of calibration, the ECU could think the engine is still cold though it is fully warmed up. This causes "open loop" operation and lower mileage. Sensor may be wrong, but not be so bad that a code is thrown. Test sensor with an ohmmeter or use a scanner with full diagnostic capability to see what the ECU thinks the engine temperature is. Fuel filter is back at the tank but if it were bad you would have problems of starving for fuel especially during wide open throttle / high rpm operation.