Big fuel mileage drop, Help!

[Hoosier 45]

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Hi all,
I have a 2003 tacoma double cab,
at about 70K I had a check engine light come on. At the time I was getting above 19 mpg back and forth to work (if I was really easy on it) and up to 25 on longer road trips at 55 mph. I drive like grand ma but it saves fuel. Anyway, Two dofferent parts stores computers said it was a front 02 sensor. I changed the O2 sensor the light stayed off after reset but my fuel mileage is down to 16 to work and 21 on the road. That is a drop of about 20%.
I checked the engine coolant temp sensor, it was reading to spec. I have driven at hiway speed for 15 miles then felt all 4 wheels brake drum/rotors, cool to touch. Iam stuck, any thought?

 

[LukeZero]

Have it scanned by a Toyota tech- not just AutoZone. The cheapy universal scanner they use at AutoZone sometimes can't catch the problems the real one with the real calibration for your engine can.

Side note- where are you in Indiana? And do you have an FJ45?

 

[Hoosier 45]

I was trying to avoid the Toyota Dealership, I am in my brother-in-laws words "tighter than tree bark". I am just north of Terre Haute, Yes I have a '65 long bed pick-up. It is in pieces right now, but all of the parts are solid with the exception of a golf ball size rust thru under the cab, that prompted the tear down. I have a 283 that came out of it for sale, has the adapter and 3sp with transfer-case.

 

[LukeZero]

This may be one of he situations where you need to pay the $79.95 diagnostic fee to figure out if you have a faulty primary o2 sensor, or if AutoZone mistakenly told you it was the primary, when in fact it's the secondary.

Also, if you have any interest- check out our Indiana LandCruiser club....Hoosier Cruisers: The Official Indiana Toyota Landcruiser Club. Or check out our corner of the TLCA boards here.
IN- Hoosier Cruisers - IH8MUD Forums

There aren't many of us (even fewer 45 owners) here in IN- always good to meet up and stick together.

Luke

 

[raydouble]

Do you happen to know the P code it was?

 

[Hoosier 45]

Sorry, I do not know what a "P" code is.

 

[raydouble]

Sorry, I do not know what a "P" code is.

A "p" code is the diagnostic trouble code.

I don't know what the A/F meter one is off hand but it should have been a P0??? or P1??? number............. They didn't tell you the code that threw the check engine light? Just that you needed an A/F meter?

 

[GRM]

Did you put in an OEM toyota O2 sensor? Sometimes the readings on the after-market ones are not as good as the OEM ones.

I think thats awesome mpg. I used to DD a 98 4runner, and always got 17-19 mpg, except for one trip where it got 23 mpg.

90k later, it still gets the same milage.

 

[InMyCruiser]

spark plugs

dont know if you the 4 or six but on my taco i have 90 thousand miles and was told by my toyota tech when i got my timing belt done that i should check my plugs he said the stock copper core plugs usually ate about worn t nubs by this time. so i bought some because my milage was suffering and i two had had a periodic engine light. when i pulled my plugs they were badly worn. the next tank of gas i was up more than 50 miles a tank and had noticably more power. i would pull a plug and check as a missfire will also trigger the check engine light.


note... the 5vzfe needs dual ground plugs or it will burn up the coils, the denso stock replacements from toyota are way cheaper than bosch plat 2's only spent like 15 bucks or somthing from the ealer auto zone wanted like 35 or 40 and thats allmost auto stores will have in stock

 

[Jetboy]

I've also heard that non-code throwing o2 sensors may still need replacing to get the optimal mileage. Many reports have said that replacement of the 02 sensors will increase mileage. I usually get 20-22 in average driving in my 96 4runner with 170k. I slowed down to 65mph once on a 200 mile trip and got just north of 25mpg. I just replaced the plugs and wires and have yet to check mileage. I went with platinum plugs. I've heard that they can kill the coils, but I'm having a difficult time believing that as the 3vz-fe in the camry which is very similar uses platinum plugs. Do they use different coils?

 

[Duane]

Yes no pratical experience but I am thinking I would stick with the OEM O2 sensors as well.
I have had a mechanic tell me as well that an O2 sensor will get "lazy" but may not actually set an engine service code.
I agree with a set of plugs if the others are worn.

I have not tried this yet but the local Toyota dealership service manager, who first became a friend through girlfriends, swears by a fuel cleaner that Toyota has where they will run your engine on a canister of chemicals until consumed which is supposed to clean out the deposits in your engine. He swears, and at first said he was very skeptical, that this has helped high mileage vehicles beyond belief.
I know my 4runner is down on power and mileage..perhaps it's just time for another tuneup/set of plugs but I think for $100 I might give this a try in the next month or so.

Logically though..if the last thing that changed was an O2 sensor and then you noticed the mileage drop...sort of points to the new O2 sensor. Sounds like the old O2 sensor even at default settings was more efficient than the new one installed.