thecorey

i know that avg milage for a 1st gen b16 w/ y1 tranny is around 25 city/ 30 hwy, cause i had one, and that's what i usually got. but, i recently bought a 91 si hatch w/ b16 swap and it was getting about 20mpg hwy. only 1 o2 was connected, it was throwing an o2 code. fixed that, added 2 brand new o2's. milage increased to about 25 highway, and 20 city. i changed the thermostat, and no help. the air filter seems to be clean. checked the vaccum lines, they arent leaking. tires arent underinflated. i hooked up a a/f meter today and its running stoich while cruising and just a little bit rich when i floor it. so i'm stumped, i'm guessing my next step would be to check the muffler?

ive read alot of stuff on this board saying to change the fuel filter, but that just doesnt make any sense. how would lower fuel pressure cause bad milage? and would cap/rotor really make THAT big a difference in milage? i'd really like to hear a qualified technician answer one of these gas milage posts with some good info rather than people just guessing what might help.

daidilus

well man if you do not believe what works for everyone else keep getting shitty gas milage

it is called volumetric efficiency.......if you get the correct AFR your engine makes max power at all RPMs....each cylinder is properly filled causing the torque curve to be wider........then you can shift earlier....and keep it outa vtec more...lower RPMS use less gas...i RPLed my fuel filter, cap, rotor, plug wires, plugs, and a bunch of other ****........20 bux at 2.85 used to get my maybe 185 miles.......now 20 bux gets me about 215, and getcho azz to the dollar store and get some FI cleaner.......you are faster and use less gas!!!

thecorey

well..i tried spark plugs first. we'll see what happens. it's just so strange that i'm getting a good reading on my A/F meter but still getting crappy milage.

Crx Jimmy

that sounds about right for gas milage 20-25 mpg is what i average, my problem is with my ys1 im in vtec all the time at highway speeds bye bye gas

virginia_dude

I have a B16A1 with Rocket motorsports cams, 65mm throttle body, skunk2 intake , 4-1 JDM header PR3 ECU properly running two O2 sensors and still see an average of 24-25 mpg with a Y-1 . THis is running TEG GSR "Hammer" rims with 205/50-15 tires

At 20 you have an issue.........at 25 your are about right. Open, flat roads and a gental right foot and you MIGHT see 30mpg. However that takes willpower beyond what I have to pull off regular.

thecorey

yeah...20 is definitely not normal..thats why i am hoping to get some good advice on how to fix it.

virginia_dude

Are you running the stock B16A1 exhaust manifold with two O2 sensors with on reading 1&3 and the other reading 2 & 4? This is important because most headers do not provide a place for these to be properly located.....Hasport is the only one I know of that makes one ready to go. I had 2 bungs welded into my 4-1 header in the proper places adn it works fairly well.

thecorey

yeah man, i have a stock b16 exhaust manifold. running 2 brand new o2's. i am pretty sure they are in the right place because when i switched the o2 wires at the ecu the car starts bogging at partial throttle. i know that is supposed to happen when you have the o2's switched. but....i'm still gonna make sure that they are in the right places tomorrow. i hooked up my A/F meter to each o2 wire today and one seems to run richer than the other, but i might not have a good connection on the 2nd o2, i'm also gonna check that out tomorrow. neither were running RICH though, they were both running mostly stoich and then got a little rich at WOT.

virginia_dude

Double check those connections....they are critical. Here is a question...what fuel are you running....I do hope you say its premium. THe ECU will retard the timing to keep 87 or 89 from knocking and it will carbon up and run like crap.

Trust me on that...I found out the hard way...

thecorey

i run no less than 93

virginia_dude

I'm giving this some thought.....since you already reversed the O2 sensors....I averaged 25 in a 50/50 mix of stop and go city driving and hiway. Look at your cap and rotor and see what it looks like...if its real crusty you can have a minor misfire thats hurting you so thats always possible...it its clean with no carbon tracking on the cap and no corrosion on the rotor thats not likely it.


If its the fuel filter you would see that most at high rpms....when the demand is highest.

After a stretch on the highway shut it down and pull plugs....take a look to see what color they are.

I am going to guess that you may have some dirty injectors.....giving you a bad spray pattern, making less power as a result and requireing you to lean on the go pedal a little harder. But not bad enough to cause a noticible misfire.....have you tried to run a can of BJ44K through a full tank of fuel? avoid the others, they are next to worthless IMHO having used them all.

Redcoupe

I have a 95 Civic Ex with Si wheels, 195/55/15s. The motor is a 95 DelSol B16a3 head, 99 Civic Si bottom end, DelSol Vtec Tranny(Y21). My mods are Injen Shortram, DC-Sports 4-1 Header, Hiflow cat with a catback (bottle neck removed) I also am running a JDM P30, AEM camgear on intake, advanced 4 degrees, B&M Fuel pressure gauge and regulator and at Idle; Fuel pressure is 40.

I am averaging about 25-26 mpg. Before I turned up the fuel pressure, I was getting roughly 28-30 in town.

It still gets killer highway mileage, but I don't see interstate too much, and if I do, it's gettin on it.

Try doing a tune-up. Is it time for a oil change? Compression good?