Hello I have a 95 civic coupe with a d16 in it and when i purchased the car it was getting around 30mpg. over the past year the mileage has gone down to around 23mpg or so. I have done no mods to it besides a clutch. I figured a tune up would help but no luck. I have replaced the fuel filter, plugs, wires, cap, rotor, air filter. I'm out of ideas any suggestions?

 

Wow...that's odd. My '00 Civic coupe averages around 38mpg. Check your tire pressure as well. That can really affect your gas mileage. Oh yeah, bad driving habits won't help either.

 

Yeah, are you driving the car the same? Is it manual or automatic? Do you have any CELs? Maybe O2 sensors are bad?

 

What about the temperature? Is it rock solid in the midle after 2-3 km - Even with the fan running on max with hot air? Could be a thermostat stuck open -> ECU runs on warmup program = more fuel injected.

Edit: It's cheap and an easy fix - I'd change it anyway :-)

 

Im thinking maybe this ^^^

 

Is the ignition timing set to spec?

 

Also jack car up and check that wheels spin free and no brakes are dragging or calipers sticking.

 

I'd start off with O2 sensor. Make sure its OEM. Universal o2s are crap

 

x2^

 

redo all of your electrical grounds, like brush off the bolts and the area between the bolt head and washer, don't scrape off any paint but blow dirt out of the threaded holes, general ground cleanup really. If you have a multimeter, check for the resistance between the ground and the battery cable and see if you can pickup any ohms.. Check the o2 sensor grounds the same way. Make sure you don't have any check engine codes. Replace PCV valve (around a $5 part)...

 

What kind of tune up parts did you replace? And with OEM or Generic parts store parts? Did you reset ECU after tune up was completed? Did you replace the PCV?

 

you don't need oem for the PCV valve, however you should check it to make sure it's working. On the new part, put the part that goes into the engine and with the part in your mouth and your head facing upwards, blow into the valve and then see if you can suck on it. You're suppose to be able to blow into the valve but not suck on the valve since the purpose of the PCV valve is that it's a check (one way) valve. If you can suck on it, keep looking. I mean I suppose you could get oem but they're typically more expensive and there is IMO no guarantee that the part will be good.

Op, what is the voltage of your car battery? Check the voltage of the battery when it's cold so as to make sure you don't have a weak battery that requires major charging. As for stuff like spark plugs and wires, go with what ever the manufacturer recommends.. Same with o2 sensors, if they say denso, use denso, if they say bosch, use bosch. Generally use denso for Japanese cars and Bosch for european cars, don't mix and match.

 

Stick with oem pcv, I went though 6 generic parts store pcv and the extra money for oem would have saved me having to install 6 times....