poor gas mileage??

2003 Honda Accord (4cyl auto) in good shape, runs well, about 24000 miles. No maintenance on the car except oil changes and did one about 1000 miles ago. Front tires are replaced recently (back tires look
very good) so they are almost new condition but I'm not getting the mileage I did on the highway. Once with a full load (4 passengers and luggage) got around 37 mpg (mileage then was about 12,000 miles) and about a month ago (same trip, mileage around 22,000 miles, less load) got around 32 mpg and now for the same trip, I'm guessing a bit less than that with less load. I'm guessing 27 to 29 mpg (I didn't fill up yet). I drove it locally a little (35 miles) before taking to the highway (300 miles) so I expect less than 37 but 27+ sounds a bit severe. What do you guys normally expect to get on the highway for this car?
I realize traffic, weather, load and speed have some bearing but just so I don't overlook the obvious, what are the "simple" things to check that I can replace and help improve the mileage? Off the top of my head is the air filter. I'm not sure about the pcv valve or fuel filter for mpg since the car runs well as far as I can tell otherwise. I hate to mess with the engine more than I have to because I'm a bit hesitant since I haven't done these type repairs in years and I never worked on this car so the placement of things is kinda new to me. Around town, it still averages around 24mpg which seems to be fairly consistent since it was new. thanks
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db wrote:

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Forget the fuel filter (read the service interval on that puppy). Put a bottle of fuel injector cleaner in the tank two or three times per year. Injectors that don't spray properly will not give good fuel mileage.
'Curly'
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motsco_ wrote:

Do you have any objective evidence that the fuel injector cleaners do any good? I mean evidence from people independent of the people making and selling the fuel injector cleaner?
Or, alternatively, what is being cleaned? Wallets or injectors?
Jeff
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wrote:

Come on Jeff, I'm the one who asked for help and he was nice enough to try. He's not asking whether I agree or you agree with him. I understand your point and I'm not knowledgeable enough to say you are right or wrong but it doesn't seem like it will break the bank to try.
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On Mon, 01 Oct 2007 16:27:23 -0500, db wrote:

All the same, I am skeptical that the injectors are the problem at this tender age. Are you using crappy gas?
In my experience, mileage can bounce a lot from tank to tank for reasons that are usually a mystery. Keep a log of every fill up and you will get a better picture of what is happening.
You mention the new tires. They may have greater rolling resistance or may be larger diameter (even if the same nominal size). We are assuming they are properly inflated.
The temperature may have dropped significantly in the last couple months depending on your location.
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I think the biggest unknown is when you fill up your tank. Is it full or not? The only way to REALLY find out is to keep topping it up until its spilling out. Of course I would never recommend doing this, as it can cause MAJOR problems in the EVAP system.
But the variance can be from 3-8 litres (1-2 gallons) which could affect mileage in a 11 US gall tank by 10-15%.
t
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loewent via CarKB.com wrote:

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The VOLUME of the fuel (litres or gallons) is printed right on the receipt. Whether the tank is totally full doesn't matter much. Overfilling is bad from the fire department's perspective too.
'Curly'
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OK... so what about the next time you fill up? Maybe the fuel froths a little more this time and the tank doesn't get as full as last time. Means your calculation will be better mileage on this tank.
Unless you actually know how much fuel is in your tank before you start filling, you will never ACTUALLY know your correct mileage on that particular tank. And there's no way to actually know how much is in there without running the tank dry (bad for fuel pump) or draining it and measuring what comes out.
Otherwise you have to settle for the variation I mentioned earlier.
t
motsco_ wrote:

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On Mon, 01 Oct 2007 08:38:32 -0500, db wrote:

Well, finally filled up and I got about 30.3 mpg so I guess that's probably okay afterall because I did some 40 miles local driving on this tankful of gas and the rest highway. I figure the 37 I once got could be the extreme best with all things working for me including perhaps newness of the car, tail wind, less traffic, etc... . My guess is the 32 to 34 is the normal for me and less than that is for misc. reasons. So while I think I might still check the air filter, likely nothing else is in too bad of shape or need of replacement. FWIW, the replacement tires are supposedly the same as the originals.
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Air filter would be the thing I would focus in on most, without a doubt. Its not real cheap but, is fairly easy. Oh and I would think even 30 mpg, with the comfortable ride you get with an Accord, is really good.
Jim
On Oct 2, 8:50 am, db wrote:

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jam wrote:

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Air filter doesn't matter nearly as much as it did in the carburetor days. A plugged air filter used to cause the carb to act as if the choke was stuck ON, especially at higher speeds. Fuel would GUSH out of every orifice as load increased. Mileage went south really fast.
Injected engines can cope better because the fuel is injected in a metered manner and the computer figures out how much air is actually flowing into the engine.
I once bought a Honda with a plugged air filter. It ran perfect.
'Curly'
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On Tue, 02 Oct 2007 07:50:28 -0500, db wrote:

I forgot to mention tho it's probably immaterial since all the highway trips were about the same speed, I set the cruise control to about 73 mph. I suppose where I disengaged it and for how long might also make a small difference for each trip. I don't recall exactly where each trip I engaged and disengaged it. And as one person mentioned, regardless of mpg, the ride is comfortable and cruise control works well for these trips I take. One thing I have noticed is when the oil has been changed it does increase my mpg tho in this case the oil isn't that old in terms of mileage ... perhaps now 2000 miles or less after this latest trip.
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