Hi folks, this is my first post, and I'm glad I found this site. Here's my problem and some background: I've owned since new a 1998 Honda Accord LX 4cyl., AT. I've done all scheduled maintenance myself including 3000 mile oil change intervals. The timing belt, water pump, and balance shafts were replaced around 112,000 miles by a local shop (I couldn't loosen the crankshaft dampner/pulley nut otherwise I would have done this myself). The car now has 149,000 miles, mostly freeway and in the last couple of months the fuel mileage has dropped from 31 mpg plus, to around 26-27 mpg. A new air cleaner, plugs, cap, rotor and ignition wires had no effect on mileage and the check engine light doesn't show. I tried checking the primary oxygen sensor with a multmeter for resistance and voltage variance but couldn't decipher the wires into the harness with my Hanes manual, plus it was 18* degrees outside. The car otherwise has good power and drives great, thanks in advance, Jerry.

 

Its expected you will lose a few mpgs as the car ages. Have you been driving a lot in city traffic, or have you recently moved to a more hilly area, winter weather, etc all those can factor in with changes in fuel mileage.

Keep an eye on it, if it gets progressively worse then worry.

 

check tire pressure too. make sure they are inflated properally for the cold weather.

 

Lazy O2 sensor(s).
It will require a OBD2b scan tool, a bottle of propane and a print out of the procedure. What you will be looking for is a value called Cross-counts. This is a measurement of how many times the O2 sensor reads variations in full Range Lean to Full Range Rich. The important point is not that it's doing this, but more-so how many times it does this within a specific period of time, and how quickly it reacts.
In effect, as the O2 sensor ages; it becomes increasingly desensitized, and can't keep up with these Mixture Range changes (It gets "Lazy"). With this increased inefficiency, gas mileage decreases.
If the "Usual Suspects" check out (the normal "Mileage Hot spots"), have the O2 sensor(s) checked out.

P

 

Thanks for the replys.
94accordsedan: driving the same routes etc.
sony224422: checked the tire pressure.
P_Adams: should I do the test, or is it cost effective to go ahead and just change the sensor(s). With the car's age and mileage I was leaning towards just replacing them and seeing what happens. Thanks everyone.

 

Unless something really strange (that I'm not anticipating) should arise (like requiring 4 O2 sensors) it may be cost effective to just replace them.
That being said, I've always advocated diagnosing b4 replacing. (I like avoiding the "Throwing Money at The Problem" thing.)
Perhaps an avenue would be to have the scan tool inquiry, forgo the free-oxygen test and replace whichever O2 sensor doesn't pass muster.

As a sidebar to this: Several domestic manufacturers call for the periodic replacement of O2 sensors as Preventative Maintaince.

P

Oh, by the way: Welcome to the Forum; a slap happy whacky place!!

 

an OEM honda sensor is like 200+. I would not replace it unless you know it is the problem. My car has 142+K on it and the O2 sensor is still functional within specs. Some other things that will cause your car to loose gas milage

1. t-stat stuck open
2. lockup not working on trans
3. carbon buildup in engine
4. dragging calipers
5. etc....

 

WoW! I'm only getting 25-26 mpg on my 2000 ex and I thought that was normal?

 

that is normal for mixed driving. I get an average of 25mpg on mixed 23 city and 31+ highway. Most of my driving is in the city.

 

Im not sure where you are from but an expected mpg drop is somewhat expected during the winter since the engine takes longer to warm up and does not operate at peak efficiency. Just something to think about before you start throwing money at the problem.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ChicoAccord2001 &raquo;</TD></TR><TR><TD CLASS="quote">Im not sure where you are from but an expected mpg drop is somewhat expected during the winter since the engine takes longer to warm up and does not operate at peak efficiency. Just something to think about before you start throwing money at the problem.</TD></TR></TABLE>

Exactly what I was going to say .

My civic during the summer months would get around 36-38 but now it's cold and I have to warm it up and it takes longer to acheive normal temps my mileage is now around 28-32.

 

Denso is about $113 at hondiscountparts.com
NGK was a little less than that.