I've got a 97 civic ex with the factory D16Y8, 4-2-1 header, intake, exhaust, OBD1 converted P-28 with boomslang harness, Phearable.net basemap, etc....
With such a basic setup i'm getting HORRIBLE gas mileage, By horrible i mean 200-220 miles per tank! Anyone have any idea what could possibly cause this??? Any help would greatly be appeciated.

 

you're probably running rich, do you beat the crap out of your motor a lot?

 

chang eyour o2 sensor?

 

No i don't beat on my motor ever. It's just a d-series so no need to! I did the obd1 conversion because my secondary o2 sensor went out and it was cheaper to convert than to buy a new secondary o2. If my first o2 sensor was malfunctioning wouldn't i throw a CEL or some sort of code?

 

im not sure if it would throw a code. i just changed mine cuz its never been changed. is there a way to check 02 sensors to see if they work?

 

you need to get it tuned. a basemap is just someone's best guess of what to set your maps at.

 

I had the same problem in my 97 civic lx sedan

 

Whens the last time you did a full tune up?

 

Run a STOCK P28 for a few tanks and see if the results are the same.

 

I've done a full tune up recently with plugs, wire, rotor, cap, fuel filter, motor flush, etc..... anyone know if it's possible to test o2 sensors????

 

Yes it is.

To do it the right way you need a scope to watch the switching voltage (Between about 100 milli volts to about 900 milli volts) It should be switching back and forth farely quickely. The exact number of switches per second escapes my mind right now.

You could do it with a regular multi meter, but they can't read fast enough to catch the switching voltage, it will just give you a average voltage number.

 

Thanks for the help, i'll try that asap!!!!

 

You can also ohm the sensor to see if its open. this works good the heater side if your O2 has one.

 

just cut the J1 jumper on your ecu and itll become a stock p28. get it solder back if u want it chipped again. your probably getting shitty gas mileage b/c of your chipped ecu.

 

if u dont beat on it then why would u even bother chipping it. the chip is whats givving u shitty mileage.

 

Return your car to stock if you want good gas mileage......

I couldn't imagine having a 16 sec. car that gets 20-22mpg!!!

My 16 *maybe 17!* second car (93 DX) gets 45mpg!!

 

I don't beat on it, i got it chipped because i had future plans for a sohc turbo setup so i went ahead and had the ecu chipped and socketed but for an all motor basemap tune for what i have now. A pretty common thing actually. Yeah it does suck having a slow car getting this shi%#y of gas mileage. Going to do a compression test tomorrow as precaution.

 

Pretty much what everone has already said. Plug your obd2 EX ecu back in and gas mileage should be back to normal.

 

Compresstion test came back perfect 210 all the way across! And I wont plug my OBD2 ecu back in because the entire reason i did the OBD1 conversion to begin with was because my secondary O2 sensor went out and it was cheaper to do a OBD2 to OBD1 conversion to disable it rather than buy a new one!