this summer I used to get 500- 520km from every full tank (50-53 liters usually) but to my surprise my last two full tanks I only gets 425(51L) and 431(52L) With same route, gas station and driving style.

The recent maintenance done:

Change plugs (same on the old ones)
Change oil and filter (same brand)
Change air filter with simota cone filter.

I’m wondering what went wrong to loss more or less 80km in one full tank.
There is no CEL , no dragging brakes, tire air pressure are within specs.
Yesterday I put the stock air intake back, guessing this is the cause, but is the warmer air vs colder air will affect that much in fuel consumption?

Would love to hear your thought and expertise

Thank you

 

While cone filters are crap when it comes to filtering, they won't affect fuel economy one way or another. Typically when fuel economy takes a dramatic plunge I recommend replacing the upstream O2 sensor (they often get lazy but don't throw any OBD-II codes).

 

No reflection on your car problem but I just have to point this out:It would be really nice to pay $1.77 for gasoline again.

 

If you have access to an obd2 scanner that can provide Long Term Fuel Trim, this may provide a clue to the problem. An intake air leak can cause ECM to compensate with Long Term Fuel Trim to maintain fuel/air mix.

good luck

 

the kind of accord i have here dont have upstream 02 sensor only downstream.

 

Thanks texas!

i don't have obd2 scanner
i've return the old plugs and she is back to the stock air duct
full tank this morning, so far so good only noticed the silence, no broooom when i accelerate
will see what happen, will report back the result....

 

485km for 51L, she's back, but i think this still not good.
i could say i'm driving 50/50 city hway.
what could be the other sign that i have a bad 02 sensor, i dont have CEL btw

 

Determining a lazy O2 sensor requires oscilloscope or advanced Obd2 scanner. It's generally cheaper to simply replace the O2 sensor (<$100) and see if improvement occurs. If you have over 100K on O2 sensor, this is a good option.

good luck

 

will try to buy and replace the o2 sensor, do you recommend any brand?

the recent full tank with 90% hway she got 320km half tank.
Is this number right for my accord?

 

A couple of comments:

• There seems to be a general consensus that Bosch O2 sensors don't often work well in Hondas, use Denso sensors instead.
• A metric of 320KM for a "half tank" doesn't really mean anything because fuel gauges are really not linear. The best way to calculate fuel economy is to fill the tank until the pump clicks off, don't "milk" it, drive until the tank is nearly empty and then fill it again. Then you have a given number of liters and a given number of kilometers which you can then use to calculate your fuel economy.