Hey folks..new guy here. I have a 2000 Accord with a F23A4 engine and M/T.
It barely has over 70k miles on it, I've only had the car for 4 or 5 months now.
The first time I calcuated MPG at fill up I got somewhere around 33 MPG. Each time after I'm seeing 22-24 MPG, I ran a Lucas Deep Clean through with fill up and managed 27 MPG once. I use nothing but Chevron or Shell gass, I generally switch between mid grade and premium each fill up. I tried treating the car like a newborn for an entire tank of gas and still got 22-24, also tried running with no a/c at all and same result. I don't really drive aggresively, I generally shift between 3 and 4k RPMs. I have absolutly no MIL's on, my A/F Ratio (O2) sensors respond as they should, no vaccum leaks anywhere, replaced Plugs-Wires-Distributor Cap/Rotor-PCV Valve with no improved results. The car seems to run fine, feels as though it has the power it should. The only other notable issue is a small water pump leak, I wouldn't think this would be related - I do plan on doing a water pump/Timing belt in the near future to fix this though. The clutch feels awesome still, nearly all driving is done on freeway with little to no stop and go. The only thing different from that first awesome fill up till now is 2 tires, I had to replace 2 Michillin's with General Altamax (Only one's my shop had in stock). It's a decent tire honestly. The door plate says to run 29 PSI...I tried upping that to 38 PSI, didn't change the mileage a bit.

If anyone has any ideas of what I can do to correct this issue please let me know.

In the meantime I will continue probing and testing!

 

My mpg is around 26 for light traffic town driving but i shift around 2500 rpm because my exhaust is loud lol, anything over 2500 rpm it sounds like i'm racing. And close to 30 mpg average city and highway combined.

 

Your fuel consumption does seem too high.

I would suspect something is causing the A/F sensors to gradaully increase fuel trim to compensate for a perceived lean mixture. This should show up as high positive long term fuel trim. If too high LTFT, an OBD2 code is set. Possibilities are intake air leak or exhaust leak ahead of AF sensor. Perhaps an engine sensor is delivering marginal information; coolant temp, air temp, MAP, MAF, etc causing skewed use of fuel map. This problem will require a good scanner and experience to detect a marginal component.

If not engine related, then there's excess load somewhere. Suggest checking brakes for a excess pad drag. Each wheel should turn w/ slight effort, perhaps 10-20 lbs force on wheel rim and there should be some pad drag.

A final possibility is fuel leakage; cracked tank, corroded fuel line, injector/fuel rail oring. An under hood leak might be detected by smell and feel. Difficult to see as gas evaporates rapidly on hot engine.

good luck

 

Mine gets better mileage when I don't switch fuels.
87 octane labeled 10% Ethanol. From the same station (usually).
Mine is the commuter car, 375-400 mi per week (80% highway 45-60mph) on about 13-14 gallons 27-29mpg.
General Altimax tires. w/P1457 CEL.
If I drive 65 or faster, the mileage drops off fast.

 

I drive 07 Accord w/ a 20 mile, 1-way commute about 80% highway and 20% urband driving. I regularly get 28-29 mpg on a tank. I drive RH lane at 60 mph or as traffic permits.

good luck

 

Thanks for the info everyone. I used my scanner to check LTFT, everything seems okay in that department. No codes at all yet. Order parts today, gunna fix my water pump leak and replace the A/F sensor. I was able to get the A/F sensor through my shop for $112! (Denso). I was pleasently suprised at my discounted price. I have also smoked the EVAP system and no leaks there. I did notice a slight shudder a couple of times during engagement of clutch today , clutch pedal feels fine though. I rechecked voltage readings on my A/F sensor once I realized it should be responding faster than a regular O2 sensor, it does seem a tad bit lazy. It makes the most sense at this point.

Will update once I see good or no results from parts change.

 

One point, you don't need to use premium fuel. This will not make any difference in fuel consumption.

One additional suggestion, check the fuel pressure regulator by pulling the vacuum reference line and sniffing the vacuum line. Any indication of fuel means the FPR diaphragm has ruptured allowing additional fuel to be pulled into the engine through vacuum line. This is rare, but has happened.

good luck

 

That could be a possibility, the car tends to idle a bit high and takes longer than any average car to drop to a good idle. I noticed a few times it smelled a little lean. I'll check the line later today. Thanks for all the advice. With the premium gas thing, I always assumed a higher octane meant a more effiecent burn therefor giving better MPG.

 

The ULEV uses a Rotary Air Control Valve in place of a fast idle valve and electric air control valve. Since you are experiencing problems with fast Idle, it seems to me that would be a likely culprit since it directly impacts both the fuel air/control and idle functions (which are problems you stated you are having). It does not sound like you are having problems with the 32 bit PCM, but it is a possibility since the PCM controls the Rotary Air Valve (as in a bad board resistor). Also, you may want to check the stoichimetric sensor in the underfloor Cat. and the Linear Air Fuel Ratio Sensor in the manifold, as both of those sensors could impact idle (at certain times) and gas mileage (all the time). Good luck. R

 

I am averaging 28mpg. I got 32 after driving through the mountains and in the city i get about 25.

Dont use premium its harder to combust (higher octane) and not only will cost you power and money but also you loose economy.

where do you drive the most?