Worst Gas Burner

I have a 1990 CRX Si, with the B16A swap from a 99-00 Civic Si. I'm having the worst luck with Gas. I fill up and after only 167 miles..... I'm on empty. I thought I had a crack in the gas tank, I looked....nothing. Maybe I have a leak on one of the hoses in the engine bay.....nothing. I have no clue why its doing this. My clutch is slipping bad, but that's going to be fixed in 2 days. Is my 02 Sensor going out? The car still pulls, and has all the power. I just can't figure it out? Any suggestions?????

When you refill, does it fill up all the way (the whole 11.9 gallons)? Does the fuel gauge ever go up and down depending on gear or anything like that? The reason I ask is because like many other cars, my car will sometimes tell me it's empty when it's anywhere from ¼ or ½ full. But as I'm driving it will go back up depending on my rpm, incline of the road, how hard I'm pushing on the throttle.

Other than that, what ECU are you using and is it throwing any check engine light codes?

I have a 1990 CRX Si, with the B16A swap from a 99-00 Civic Si. I'm having the worst luck with Gas. I fill up and after only 167 miles..... I'm on empty. I thought I had a crack in the gas tank, I looked....nothing. Maybe I have a leak on one of the hoses in the engine bay.....nothing. I have no clue why its doing this. My clutch is slipping bad, but that's going to be fixed in 2 days. Is my 02 Sensor going out? The car still pulls, and has all the power. I just can't figure it out? Any suggestions?????
Fuel pressure check.. Could be a leaky injector. You need to check if you hold pressure with the engine off.
Is it hard to start with alot of black smoke just after it starts?

Could also be your fuel pressure regulator. Pull off the vac hose to the regulator and inspect it, if dry you are OK

Good luck
SH