I've had my 97 LX for about 6 years. It has about 120,000 miles. Because I'm always curious about my gas mileage (can't help it), I've always been in the habit of checking my mileage after every fill-up.
My question in brief
The problem I'm posting about is that my mileage always averaged 22.5 overall until it suddenly dropped to averaging 18 mpg around June. I have had 2 Honda dealers and a Honda specialist look at but apparently they rely solely on codes to diagnose problems and the only code I've had seems to be unrelated (so I'm told).
Recently, I realized that since my mpg has been bad, my "low fuel" light doesn't come on as soon as did before. The last time it came on I figure I had less than a gallon of gas left in my tank (it used to come on with 2 or 3 gallons left - back when all was well). It took me a while to realize and figure this because I don't normally run it so low. But I had noticed previously that the needle looked awfully low for the fuel light to not be on yet.
So I'm wondering (since the Honda mechanics are no help) if it's a clue to my mpg problem that fuel light takes longer to come on than it used to.
In case it matters, here is what happened leading up to, and since, the mpg trouble started:
1) In June the Check Engine light came on.
2) After a week or two I took it to Advance Auto. They read the code (I've forgotten the code number now) and turned off the Check Engine light at my request so I could see if would come back on.
3) About a week later it came back on, so I took it back to Advance and they read the same code and turned off the light again.
4) It came back on again a week or so later, and after a couple of weeks I took it to Honda dealer#1 for repair.
5) Honda dealer#1 said I needed a purge control solenoid valve (which was what the guys at Advance Auto had speculated) and also a canister, which would cost $700.
6) Shocked at the cost, and having read that I wouldn't hurt my CRV if I didn't do the repair immediately, I declined the repair and picked it up. (They turned off the CE light)
7) Starting with the very next fill-up, my mileage went from 22.5 mpg average to 18, and has been there ever since. (It had not changed at all until the dealer had it. The CE light had never affected it.)
8) This time the CE light took 5 weeks to come back on. When it finally did, for a second opinion, and because of what had happened with my mpg, I took the CRV to Honda dealer#2.
9) I showed them the CE light and told them about the bad gas mileage that was happening. They diagnosed the fix for the CE light as being the same problem as dealer#1, but said the repair and a tune up would be covered for free under Honda's "good will" program, so it all cost me $zero. However, they couldn't find an explanation for the drop in mpg.
10) So the cause of my CE light was fixed, but the bad gas mileage continued.
11) I looked on the internet and found that a bad front o2 sensor could cause bad gas mileage, so I replaced it (myself) with a Bosch Direct OEM replacement model (not a genuine Honda). No change.
As I said I am trying to figure out why my mileage has gone down so much. Does anyone know if it might be related to the fuel light taking longer before it comes on than it did when I had normal (good) gas mileage?
Or, what could it be?
Thanks for your help.