I have a '94 civic ex with an obd2 b18b1, virgin obd1 p75 ecu, intake, exhaust (2.25 inch piping with bobo muffler) and si tranny which is giving me about 17-18 mpg (170 miles per tank) on a good drive (a little spirited). I previously had an ls vtec with a virgin p28, ls tranny, intake and exhaust (stock muffler, 2.25 inch piping) and on a good drive (a little spirited) i would get about 240 miles per tank. I don't know why such a horrible drop in gas mileage.

 

when was the last time u gave it a real good tune up? also, any cels?

 

I changed spark plugs about a month ago, but still have the same fuel filter (which is not clogged), the same cap, internals and spark plugs wires (from obd1 dizzy).

 

Oh yeah no cel

 

Every Integra I have ever owned has gotten between 28-33mpg (obviously all B series). I have had 5, maybe 6 Integras.

 

Well may have a gas leak somewhere?, the 2.25 piping makes you loose a little bit in gas mileage, and if you say it has a tuned pcm it probably have the car running really rich do you smell gas?, is your exhaust pipe covered in black?

 

No only the inside of the muffler. I don't smell gas either.

 

It could be that used pcm thats been tuned giving you that horrible gas mileage, or id try doing a basic tune up plugs, wires, air filter, check your tire pressures too that changes your gas mileage!

 

I don't even know where to begin looking for the gas leak either. The fuel rail and the pressure regulator are all dry.

 

simply the gas lines that run underneath your car and your gas tank!, the lines get really rusty depending on where you live or the car has lived part of its life

 

I would say if it is a leak, and it's not the rail or regulator the problem is more than likely going to be the connections at the tank. They usually go bad before the lines do.

 

The problem is something that did not happen gradually. It happened since I put the engine in.

 

Must be the Fuel Delivery or the PCM then

 

I've had a 93 CX hatch running B18B1 with 2.5" exhaust system for about a year, and I get around 25-27 mpg around town every tank.
I wind it good through the gears most every red light also.
If you have a leak in engine comp, you'll see or smell.
Mine has new timing belt, valve adj, new plugs, cap, rotor from a year ago.
Good tuneup makes bunches of diff.