Question for you car gurus

[ken brydson]

The gas mileage on my '04 Honda Odyssey (121K) has recently fallen off tremendously. I used to get 330-350 miles per tank mixed driving. As of late it's dropped to 250-280. I took it in to the dealer for an oil change and they suggested an injector service($160) should cure it. I had about 1/2 a tank and around 180mi at the time. The guy told be to run that tank through to flush out the treatment stuff and then fill as normal. Well on the rest of that tank I ended up at 320 miles. I thought great, fixed! Not so much, next tank 240 (14mpg), worst ever.
With gas at $4gal, any suggestions highly welcomed. TIA

[disneyjoe7]

SeaFoam Google it, YouTube it. Use it. You'll be happy.

[bobman1235]

It's SeaFoam . Funny when you tell someone to Google a product and can't even spell it right.

[disneyjoe7]

Sorry my Bad.

[Jstas]

Have you changed the air filter lately? Especially this time of year with all the pollen in the air. Pollen has a resin on it that lets it stick to stuff. It also collects dirt when stuck to say, an air filter. Clogs 'em up good. Can really make a difference in gas mileage.

Also, might want to put in a new fuel filter if you haven't already. You can do all of that at the same time. Also, check at least one spark plug. See if it looks ok or if it's covered in oil or white crusty stuff. Both could be attributable to other problems. If the plugs look OK and you change the fuel and air filters and your situation doesn't improve, then get the injector service. With 120K miles though, I don't think you need to be concerned about a fuel injector cleaning. At least not on a 2004. On a 1994, I'd say yeah, get it done. An '04 though, that shouldn't need it unless there's another underlying problem.

[ken brydson]

Have you changed the air filter lately? Especially this time of year with all the pollen in the air. Pollen has a resin on it that lets it stick to stuff. It also collects dirt when stuck to say, an air filter. Clogs 'em up good. Can really make a difference in gas mileage.

Also, might want to put in a new fuel filter if you haven't already. You can do all of that at the same time. Also, check at least one spark plug. See if it looks ok or if it's covered in oil or white crusty stuff. Both could be attributable to other problems. If the plugs look OK and you change the fuel and air filters and your situation doesn't improve, then get the injector service. With 120K miles though, I don't think you need to be concerned about a fuel injector cleaning. At least not on a 2004. On a 1994, I'd say yeah, get it done. An '04 though, that shouldn't need it unless there's another underlying problem.

New Iridium plugs were installed when I did the timing belt service @ 111K. I'll pick up a new air filter and fuel filter and give that a try. Any rec for brands? I've always used Fram but I've heard here on CP that their oil filters suck. Their others as well?

SeaFoam looks interesting. May look into that too if the filters don't help.
Thanks guys!

[nguyendot]

Air filters, tire pressure, fuel cap, reset the ECU, seafoam, new plugs.

There are so many things to check, but those are the importante ones there. Also, the fuel you use might suck too, ethanol is no good.

[ESavinon]

Wix for oil and K&N for air.

[TNRabbit]

Single most significant cause for major drop in fuel economy at that mileage is OXYGEN SENSOR. Replace it & I'll bet you see at least 3-5 mpg increase.

DO NOT use a Bosch on a Japanese car. Go with Denso or NGK (NTK for O2 sensors).

[RuSsMaN]

Also, might want to put in a new fuel filter if you haven't already.

My thoughts ^.

[zingo]

Good call on the O2 sensor. Any of that emissions that provides feedback to the computer can cause issues even if it isn't throwing codes.

[TNRabbit]

Also realize there are hardly any gas stations any more that DON'T include 10% ethanol in their fuel. There's about 2-3 mpg right there.

Ethanol wreaks havoc on small engines, especially 2 strokes (gums up the fuel system).

[nguyendot]

Totally forgot the fuel filter and O2 sensor...good callouts. Seafoam is really fun on the really dirty cars. It doesn't do much for mine since it's direct inject and the fuel never actually hits the valves...

[Jstas]

New Iridium plugs were installed when I did the timing belt service @ 111K. I'll pick up a new air filter and fuel filter and give that a try. Any rec for brands? I've always used Fram but I've heard here on CP that their oil filters suck. Their others as well?

SeaFoam looks interesting. May look into that too if the filters don't help.
Thanks guys!

Well, since I have Fords, I use Motorcraft parts. But you have a Honda so that doesn't really work for you. My secondary choice is usually Purolator unless they don't have the part I need. Then it's Bosch or WIX if I can find it in that. Some Hondas though, I've had to get fuel filters from the dealer because it was such a specific part. And check out online at any number of Honda forums for a procedure on how to replace the fuel filter. There might be a fuel pump cut-off switch you need to trip before you do it or your quite expensive gas will go shooting everywhere.

Check out: http://www.rockauto.com

They have a real nice Java based catalog with a very accurate cross-reference. Find the parts you need and then call your local Pep Boys, Autozone, NAPA, Advanced Auto, Kragen, Mom and Pop place or whatever you have near you and see if they have it and for what price then buy the cheapest one or the one from the small business.

As far as FRAM goes, way back when, in the 80's, they were still made here and they were great. Then manufacturing was shipped overseas and the quality control just went in the toilet. They don't always fit right, gaskets are bad from the factory, tolerances are all wrong and so on. I just started avoiding them completely after 3 or 4 times in a row trying to get a filter that sealed right or didn't have defects before all the bad press on the Internet came out.

Oh and about Iridium plugs. Alot of Lightning guys were using them and raving about them. Until the bonded Iridium tips started shattering and breaking off from the heat and pressure of the supercharged engines. They would see similar gas mileage hits because the spark gap opens up a good deal and reduces the intensity of the spark. That causes an uneven fuel burn for a rich condition which destroys gas mileage alot like what you are seeing. If you take a quick whiff of the exhaust after the car is warmed up, if it smells sweet, you're running rich. It's either the spark plug problem or not enough air caused by a clogged air filter in most cases. If it smells like rotten eggs a bit, you're running lean and the fuel filter is probably clogged.

You should probably still check the plugs though. Just pull the 2 or 3 you can reach easy. Pull one, check it, replace it and move on to the next. If you have a magnifying glass, grab that and when you pull one, look at the tip of the electrode coming out of the white ceramic insulator. If you can see cracks, they have gone bad and are likely your problem. Modern platinum plugs should be all you need to get the performance you want. Autolite or NGK plugs will work like a champ for you. NGK V-Power plugs are stellar performers and we used them in dirt bikes and race cars all the time. But if the Iridiums look ok, then they probably aren't your problem.

[Jstas]

Single most significant cause for major drop in fuel economy at that mileage is OXYGEN SENSOR. Replace it & I'll bet you see at least 3-5 mpg increase.

DO NOT use a Bosch on a Japanese car. Go with Denso or NGK (NTK for O2 sensors).

???

Bad advice here. Well, expensive advice really. One, the O2 sensor would cause rough idling, rough running, hard starting and more likely than not, have a dash light lit. On a 2004, it would have a code and show a light if it was out of whack enough to cause fuel mileage problems that amounted to a 30% reduction in efficiency. If it doesn't do any of the above, replacing the O2 sensor would just be throwing good money after bad. If the O2 sensor is fouled or on it's way to being fouled, there are other problems causing it and you need to address those first. Otherwise your nice new O2 sensor will be fouled again in a few months.

Two, as far as Bosch on a Japanese car, that's a load of crap. Sorry, but it is. Bosch Platinums are sometimes the only available plug and sometimes the only available filters as well. I've used Bosch stuff on cars from all continents with zero problems. Yes, Denso and NGK are preferred because they are Japanese OE Manufacturers but Denso is hard to find and not every store carries a full stock of NGK.

[camp21178]

Single most significant cause for major drop in fuel economy at that mileage is OXYGEN SENSOR. Replace it & I'll bet you see at least 3-5 mpg increase.

DO NOT use a Bosch on a Japanese car. Go with Denso or NGK (NTK for O2 sensors).

Good call on the O2 sensors.My old Toyota Tacoma had the opposite symptom, the O2 sensor was bad, but at 249,000 miles I was getting the best mileage ever. It was running lean, but I didn't care.

[gdb]

Have you recently resumed use of your A/C ? That takes more fuel, along with the many other possibilites.

[billbillw]

Make sure you brakes aren't grabbing. After a 10 minute casual drive, stop and see if any are red hot. Also, note your engine RPM at cruising to make sure the transmission is shifting all the way to its top gear.

Just curious, over what period of time are you basing your per tank range average? More than a year I hope. Seasonal variance can be significant. Outside air temp, use of AC, fuel formulations, etc. can all affect the fuel economy.

[heiney9]

Has your routine changed recently?

I just moved and it's about 10 miles city driving to work vs. 1.5 miles previously. I use more gas (gallons) but on average I get about 3-4 mpg better fuel mileage. Operating a car for a couple miles each way is much less fuel efficient than driving 10+ miles each way.

It's a catch 22 though because in the end you use about the same amount of gas (in gallons) each week but you get better avg. mpg.

[Sherardp]

It's SeaFoam . Funny when you tell someone to Google a product and can't even spell it right.

Bobman is the grammar/spellcheck police around these parts. You have tread lightly or he will nail you. Got me a couple times I must admit.

Anyway +1 on the Seafoam. Works very well for injector cleaning. I would also recommend Redline Injector cleaner as well.

[dorokusai]

BG44K.

www.bgprod.com

[fastz28]

o2 sensors can go bad and not throw a code and mileage suffers

[bobsauto49]

All obdII cars will set a ck eng. lite if the o2 is that far out of range! And that fuel mileage is way out of range! Sea-Foam is the best product i sell,(as far as doing what it says its gonna do)Try a can of that to a half tank of gas,ck,or change the air and fuel filter! I own a Carquest store,so i'm partial to Wix! However,any top brand(-fram)will be suffice! If your on the rite track,u should notice a difference on your next fill up! If not,there should be a ck.eng lt. by then! P.S Sea-Foam is great for ALL vehicles!!

[fastz28]

o2 sensor can be frozen at a certain volt will not send code and be bad
I build race lt1s and ls1

[fastz28]

sea foam is pretty good half a can in gas tank and other half in brake booster vacuum hose

[TNRabbit]

All obdII cars will set a ck eng. lite if the o2 is that far out of range! And that fuel mileage is way out of range! Sea-Foam is the best product i sell,(as far as doing what it says its gonna do)Try a can of that to a half tank of gas,ck,or change the air and fuel filter! I own a Carquest store,so i'm partial to Wix! However,any top brand(-fram)will be suffice! If your on the rite track,u should notice a difference on your next fill up! If not,there should be a ck.eng lt. by then! P.S Sea-Foam is great for ALL vehicles!!

O2 sensors HARDLY EVER throw a check engine code.

[ken brydson]

Hey guys. thanks for all of the feedback. I'm looking into all of this. I've never figured out how to multi quote so I'll answer some of the questions I remember...

-observation based on the length of time I've owned it. Always have got about the same MPG. A/C use? I wish... we've had a crappy spring here in W Wa. Only a handful of days into the 60's, yet to hit 70.

-no change in routine. I sell real estate so I drive all the time for work. Pretty good mix of city/hwy

- is there a way to check the o2 sensor?

Thanks again...

[bobsauto49]

O2 sensors HARDLY EVER throw a check engine code.

I hook up cars/light trucks approx. 40 times/week to my OTC genisys,and see about 4 to 10 o2 sensor codes/week! Whether it be the heating element,or a lean,or rich code! Some which can be caused by a vacuum leak,or clogged convertor,or a bad o2 sensor,among other things! Fact is, we get paid a higher hourly wage at the shop rate,cause of our education(which is updated several times/year),and the thousands/year spent on new,ever changing equiptment/tools! There,I vented,and feel better! Good Day!

[ken brydson]

sea foam is pretty good half a can in gas tank and other half in brake booster vacuum hose

Question on Seafoam...a couple ot he youtube vids I watched on it suggested 1/3 to the tank, 1/3 to the vacuum hose and 1/3 to the crankcase. Thoughts?

Oh, and I think the air filter may be part of the problem... pretty nasty