Hey everyone. I got a 98 civic hatch with a b16 head a couple months back and I have had extreme issues with fuel consumption. Im probably averaging about 15mpg. Any ideas on what it might be? ECU, Air sensor?

 

Assuming the CEL is not on (does the CEL work?) the most common cause is the cam or spark timing is wrong. Adjustable cam gears should be set to zero unless you're racing and someone with experience is tuning the engine.

Make sure the fuel pressure regulator has the vacuum hose hooked up to it. Without the vacuum, fuel pressure will be too high. If it's an adjustable regulator, get rid of it and go back to a stock one.

Also it could be a fuel injector stuck open or something. Check that all 4 cylinders are working about the same by removing the spark plugs to examine their color. If one is black, that cylinder is running too rich or has an oil issue.