Super bad Mpgs on my 04 gx
 

Hi everyone,
I have a 04 GX470 that is getting very bad Mpgs
I have tried to do everything that is possible to get it better but nothing have changed now is doing only 9mpg on city and 12 on highway.
I have changed spark plugs, oxigen sensors, air filter, cleaned MAFS, new tires and lastly I had done the timing belt water pump and thermostat service.
when I got the truck it had 70k miles now in at 116k and is killing me.
please if anyone knows something that I might be missing to do to get a better MPGs I will appreciate the help.
thanks.
rob.

1st... how are your driving habits? Do you floor it a lot? Do you drive down the interstate at 80mph instead of 70 mph?
do you tow??

2nd... any mods? Lifted, type of tires? Heavy sliders?

3rd... did the gas mileage get worse after the timing belt was replaced?

4th... does the acceleration seem sluggish?

Answer those please.

Hi MrJason,
Thanks for responding.
I drive normally and specially now that I been getting so bad MPGs.
on highway I do drive between 65 -75mph but no mere that that.
I do not tow
I use the same tire factory tire size
MPGs got worst after a O2 sensor failed, after that I got replaced all O2 sensors and the rest of the work I have done in it.

Thank you and hope this info can help me to solve this.

rob.

Are you going by the dash display?...or your fuel receipts, odometer and calculator? I trust the latter far more than the former.

MPG got worse after O 2 sensors failure and hasn’t improved? May need to change all the sensors regardless of check light. They have an end life even before total failure and they are what is mostly responsible for drop in gas mileage as the truck ages and their function deteriorates.

I do it myself with gas receipt and count the miles

I have replaced all 4 O2 sensors about 8 months ago

Sounds like you need a mechanic that can put a scope on the O2 sensor readings. He should see the output change over time as it cycles.

http://www.autodiagnosticsandpublish...r-testing.html

And I second the comments about driving habits. I get my best highway mileage when I stay below 2000 rpm.

Chip H.

Sounds to me like possibly 3 things.

1...your converters have too much soot build up.
But this would be accompanied by a lack of acceleration.

2... be sure the timing belt is on the right notches. Toyota/Lexus has a funny thing with th variable valve timing... they can be off by about 10 degrees and cause a loss of power and mpg.

3... intake runners are stuck in high rpm mode. This would cause a lack of lowend power and mpg/ if it’s stuck in the low rpm position it would cause higher rpm power loss and mpg.

If it makes you feel better i get bad MPG too... last tank i averaged 12.9 Mpg.

granted im lifted with 33" ATs and they were mainly all city commutes to work in traffic LOL... but it still sucks i feel your pain... sort of.

My 05 GX is stock and has new plugs and timing belt. I’m averaging 18.5mpg.

One more question... do you sit and idle a lot? Like on lunch break?

I've had my '04 for about 6 years now, it averages about 14mpg mixed use. The '05+ get VVTi, which may make a difference in economy. My personal BEST with this truck is about the same as @MrJason averages, lol.

@Robclzr What is your tire pressure at?

no I don’t.

I would be very happy if mine averaged 14mpg.
in city driving I’m lucky if I get 10mpgs

tire pressure is at 35