I have an 04 rx 330 that for the life of me I can’t figure out why I’m having fuel issues. I’m not sure if it’s an electrical issue in my dash or my fuel pump sensor. I run til I’ve got the fuel light on and I’ve noticed even when it says I have 0 miles left, I only am able to fill up 16.7 gallons. I checked and cleaned my MAF sensor a day ago so that’s not the issue. I have a mechanic who’s gonna check the dash with a multimeter to see if that’s the issue because honestly if it’s the fuel sensor, I can’t be assed. Rn I’m getting about maybe 230 miles for each tank when I fill up and I’m filling up every week. I switched to chevron gas because the whole tier of gasoline hoping that would help but it’s been months and I’ve yet to see an improvement. This is literally making me crazy because there aren’t any codes. Everything else seems fine. Yet I can’t seem to figure it out. Moreso posting for suggestions or if anyone knows an issue that could cause such crappy fuel economy outside of the ones I’ve listed (I did get an alignment a few months back and new tires about a year ago). Help pls?

 

No it's not an electrical issue in your dash. IF you're truly putting in 16.7 gals and only getting 230 miles that means you're getting <14 mpg. For reference I now average @23-24 mpg all around driving
You do not mention you're driving style (heavy footed?). I've driven with several women who seem to think they have to either be on the accelerator OR the brake all the time, never coasting when approaching red lights or traffic they are always pushing one pedal or the other which is very hard on the car and destroys mpg. I've doubled the MPG on a girlfriends car simply by driving technique. (BMW X5 and a Honda CRV)

• Lots of very short city runs in stop-n-go traffic OR hwy/frwy mixed in?
  • on the hwy what are your speeds? wind resistence goes up as a square to speed meaning there is a LOT more resistence at 75 mph than there is a 65, and a LOT more at 85 than there is at 75 mph.
• When was your last "full service" tune-up?
• How do you drive teh car when it is cold? Are you really taking it easy until the motor warms up or blasting away all the time?
• Is your car showing any codes currently? Do you or your mechanic have access to a code reader?
• How did you "check and clean" your MAF? If you touched the end of the element you likely damaged it. Did you reset the ECM afterwards? If not your cleaning has not yet taken affect it takes some miles to readjust (see note below)
• How many miles on your car?
• Have you had any recent work done on the car?
• Are your plugs and coils OEM or aftermarket? Are your plugs >100K miles old?
• When was your last timing belt change? It needs to get done at 100K miles along with the waterpump and bearing but that is not your current issue here
• What is your avg speeds?
• What tire pressure are you running?
• Flat or lots of hill?
• When did you last change your air filter?
• What is the MPG your dash gauage states you're getting? Yes you have a pretty inaccurate gauge but one is there to give youa ballpark - see owners manual
• What is the condition of your lower control arms? Have you had them changed out in the last 100K miles?

Changing to "Chevron" means nothing any top tier gas is equal - ARCO, Costco, Shell, Exxon, etc all the same aside from a very slight additive perhaps but it will not fix any problems nor give you better gas at one ove rthe other. Our cars take lower octane so you're wasting money using higher octane is does zero improvement contrary to some people's beliefs.
I posted a year or so ago how I quickly raised the MPG on my 2004 RX330 AWD now avg @23 mpg overall try those things most cost nothing and most are very quick and easy (use "Search" look under my name and "MPG". Dont assume because you got an alignment it was done correctly, I got one 3 years ago took a roadtrip the steering wheel was way off as they botched it the first time.... I've driven MI roads they are the worst I've driven in any state so far, could be alignment it out again

Likely culprits:

• You're in Michigan with salted roads that really suck bad so you have much more chance of torn LCA's, shot wheel bearings and/or calipers dragging/brakes sticking than western areas.
• Dragging brakes - drive your car for a bit then feel all the calipers, is one or more "hot", not just warm but hot?
• vacuum lines - yours desperately need replacing as they are brittle and possibly cracked - replacement costs are <$20
• dirty MAF and throttle body, clean your O2 sensors and disconnect your batttery for a couple minutes to reset the ECM (you'll have to reset your windows, sunroof, and hatch afer doing this), resetting ECM will make the car relearrn your driving style over maybe 50 miles so ti will feel different for that time. None of this costs anything but a little bit of time and a can of MAF cleaner from Walmart. Do this all at once so your ECM can adjust properly - total cost is one can of MAF cleaner @$7
• running lower tire pressure - I run mine at 40 PSI

Other simple remedies or potential problems:
Run a can of Seafoam in your half-filled gas tank (pretends to clean fuel lines and fuel injectors), also run a pint through the vacuum line going into your intake manifold but do that one slowly while car is running (helps remove carbon from your pistons and valves). At your mileage I'd strongly suggest also running one in your crankcase about 100 miles before an oil change to remove sludge buildup (this makes a big difference in how clean your oil will be). A can runs $8 at Walmart or Amazon you'd need 3 cans

Clearly DIY is not your thing. Stating that you have a "mechanic" means little unless they are a "competent" mechanic, don't assume competence in anything as I've seen a LOT more bad ones than good ones and NEVER take your car to Firestone, Midas or other generic garage thinking they're decent. Most of what I wrote is free and should be done anyway on any 20 year old RX or even any car. A DIY'er or decent mechanic could do the more simple stuff in @2 hours at very minimal cost (clean MAF, clean throttle body, replace all vent lines, run Seafoam, clean the O2 sensors, pump your tires to 40 PSI all that is maybe $50 in parts and needs to be done anyway). Checking your lower control arms along with the ball joints and sway bar bushings and sway bar links takes maybe 15 minutes they can also inspect brakes sticking then too but driving it is more reliable for checking the brakes sticking

Good luck

 

Most of my driving is local.
Traffic light to traffic light and usually 45 mph areas.

I only get 14 mpg according to the info display on the dash.

On the highway I get 26-28.

Our cars don't get great mpg for slow and local busy traffic.

 

Do it the old tried method: Fill up full tank, you knw how many gallons put in. Drive until you hit "E" and then you can find Miles/Gallon! When I fill up I look at the mileage make a note and zero it again. I do it every single fill up.