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Poor gas mileage

Tiny
EVERCLEVER62
  • MEMBER
  • 2012 SCION XB
  • 2.4L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 111,000 MILES
After I fill up my tank, the digital gas gauge only shows 167 miles of range. It used to be 310 +/- 15 miles. The analog gauge always goes from E to F when gassed up. You would guess that the sensor was off but whenever I need to gas up again. Both the analog gauge is near F and the digital gauge displays just 15 to 30 miles range remaining.

My tank holds 14 gallons and I typically need 12 to 13 gallons with each fill up.

I've replaced the spark plugs, air filter and used fuel injector cleaner (3 bottles) plus used the Marvel Mystery Oil additive with each tankful but nothing has improved. It also passed the state emissions check recently. There's no smoke coming out of the tailpipe.

The car accelerates briskly and cruises at highway speeds effortlessly without sputtering, stalling or misfiring.
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Thursday, July 7th, 2022 AT 10:52 AM

31 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

Have your driving habits changed? I know if you are getting fewer miles to a gallon, it will change the miles to empty.

Have you checked the fuel mileage you are getting? For example, write the present mileage down, fill the tank, drive for a few days, refill and divide the miles traveled by the number of gallons required to refill the tank? That will provide what you are getting per mile and then you can compare that to what is being identified by the vehicle.

Let me know.

Joe
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Thursday, July 7th, 2022 AT 2:23 PM
Tiny
EVERCLEVER62
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  • 16 POSTS
Thanks for your response, Joe. To answer your questions, no, my driving habits haven't changed as I am not now a 'Lead Foot Louie'. I used to average mid 20's MPG with a mix of city and highway driving. Now it's 13 +/- 2 MPG.
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Thursday, July 7th, 2022 AT 2:29 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

As far as driving habits, I meant did you change where you drive? For example, are you doing more in town driving?

Regardless, this vehicle should be getting more than 13MPG. Have you noticed any odd odors from the exhaust that could indicate a rich fuel mixture? Also, by chance do you have a scan tool that can read live data?

For the mileage to have changed that much, first, make sure the air filter is clean. If it is excessively dirty, it will cause a rich fuel mixture. Also, if you do have a scanner, let me know what the short-term fuel trims are when the vehicle is at operating temperature. Additionally, check the coolant temperature sensor signal is accurate. For example, if the engine is cold, the sensor should indicate near ambient temperature.

Let me know. If you don't understand what I'm saying, let me know.

Take care,

Joe
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Thursday, July 7th, 2022 AT 5:14 PM
Tiny
EVERCLEVER62
  • MEMBER
  • 16 POSTS
Type of driving hasn't changed. But the core of this issue is when I get gas, the digital gauge only goes to half what it used to but it's accurate as to my available range.
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Thursday, July 7th, 2022 AT 5:26 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

There is only one fuel level sending unit. (See pic below) When you say digital, do you mean there is a digital and an analog fuel level gauge? Let me know.

If that is the case, we need to get our hands on a live data scan tool. I need to know fuel trims, if the oxygen sensors are responding, and if the coolant temperature sensor is working properly.

Let me know. Also, if you haven't changed the air filter in a while, check it. I've even seen mice make nests in the box causing air flow restrictions.

Take care,

Joe
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Thursday, July 7th, 2022 AT 5:38 PM
Tiny
EVERCLEVER62
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  • 16 POSTS
The air filter was replaced in April. The digital gauge I'm referring to is the mileage 'Range' indicator that gets smaller as gas is burned.
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Thursday, July 7th, 2022 AT 5:51 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

Okay, that makes sense. I was wondering why you had two fuel gauges. LOL So, it sounds like we need to do some checking. By chance, can you get your hands on a live data scan tool? That will tell me a lot as to how much fuel the electronics see as being used. Also, I suspect the check engine light isn't on. If it is, have the computer scanned for diagnostic trouble codes. Most parts stores will do it free of charge.

Next, I need you to pay attention to any strange odors from the exhaust. When it is sitting at idle, open the door and take notice if it has a strong exhaust smell.

Let me know.

Joe
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Thursday, July 7th, 2022 AT 7:53 PM
Tiny
EVERCLEVER62
  • MEMBER
  • 16 POSTS
The 'Check Engine Light' is not on.

Tailpipe fumes do not have a weird odor.

Would an auto parts store have a live data scan tool that they would do those free tests like with a battery check?
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Thursday, July 7th, 2022 AT 9:02 PM
Tiny
JIS001
  • MECHANIC
  • 3,411 POSTS
Do you reset the mileage range every time you fill up? I do this because your driving habits can change. For me as an example. I drive 5 miles round trip and my computer says 14 MPG. If I cruise on the freeway and I mean no braking just steady, it jumps to 24 MPG. If I sit and idle in my car with A/C, then it goes down drastically. But I like taking naps with my A/C on.

The point is, I reset my trip every fill up. And I see how many miles I get every time I fill up. So, in my head I know what my average is. If you don't reset the computer "average" you are only looking at your average since first use which will be disappointing. If there is no check engine light, then there is no problem.

Now if you feel there is an issue, I would recommend you have the tires aired up to spec when the tires are actually cold. Fill the tank up and reset trip A or trip B to zero and post a pic. Reset your average speed on the display to zero. Drive to empty and post a pic of the trip mileage with the low fuel and average speed to see if there is an issue.
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Thursday, July 7th, 2022 AT 9:42 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

Many of them have scan tools to check for codes. I'm not sure if they would have one to provide live data. Try contacting one and see what they say.

Joe
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Thursday, July 7th, 2022 AT 9:45 PM
Tiny
JIS001
  • MECHANIC
  • 3,411 POSTS
I just wanted to add on the resetting the computer trip. I had a 2020 Honda Civic. My 5-mile round trip MPG overall was around 18MPG. When I took a job 23 miles away my MPG jumped to 31 MPG because I was cruising 64-70 miles an hour with no braking, and I was resetting my computer. Trip A was from mileage at 0 = 18 MPG. Trip B was when I reset my computer at fill up. So, I saw the MPGs at that fill up.
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Thursday, July 7th, 2022 AT 9:50 PM
Tiny
EVERCLEVER62
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  • 16 POSTS
Attached is the AutoZone scan showing no issues. It's not a Live Data Scan and suggested I go to a mechanic for that.
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Saturday, July 9th, 2022 AT 10:33 AM
Tiny
EVERCLEVER62
  • MEMBER
  • 16 POSTS
Here's the best rated Live Scan Tool for $120.00.

Does this also fix or just detect issues?

If it fixes problems, how easy is it for a non-mechanic to do that?

Www. Amazon. Com/BlueDriver-Bluetooth-Professional-iPhone-Android/dp/B00652G4TS/ref=sr_1_4?Crid=3U1PHV5UZBE7I&keywords=bluedriver+pro+obd2+bluetooth+car+scan+tool&qid=1657389317&s=automotive&sprefix=BlueDriver+Pro+OBD2+%2Cautomotive%2C253&sr=1-4&ufe=app_do%3Aamzn1. Fos.F5122f16-c3e8-4386-bf32-63e904010ad0
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Saturday, July 9th, 2022 AT 10:57 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

The Blue Driver is a decent tool. I keep one in my vehicle all the time. It hooks up to your phone (at least mine does). The one you are looking at is the same as I have.

It's on sale too. As far as a scanner, any scanner, they are nothing more than a tool designed to communicate with the vehicle's computer modules and provide possible issues. They can't fix the issue, but they usually point you in the right direction for repair.

Let me know if that helps or if you have other questions.

Take care,

Joe
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Saturday, July 9th, 2022 AT 10:53 PM
Tiny
EVERCLEVER62
  • MEMBER
  • 16 POSTS
AutoZone had a tool for $600.00 that they claimed would do both, find problems and fix them.
Www. Autozone. Com/test-scan-and-specialty-tools/professional-code-reader/p/innova-smart-diagnostic-system-tablet/1062521_0_0
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Sunday, July 10th, 2022 AT 12:46 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

That is a decent scanner, but it won't fix the problems. It will identify the most common fixes. They told you it would fix the vehicle?

Joe
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Sunday, July 10th, 2022 AT 7:47 PM
Tiny
EVERCLEVER62
  • MEMBER
  • 16 POSTS
Yep, just push a few buttons or something to that affect and it would reset / reprogram the software.
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Sunday, July 10th, 2022 AT 8:17 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

It will erase or delete a code, but it won't fix the problem. I don't want you to be misguided. The repair will need to be done by a person.
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Sunday, July 10th, 2022 AT 8:56 PM
Tiny
EVERCLEVER62
  • MEMBER
  • 16 POSTS
I went to a mechanic today and they did six live data scans (I can attach screen shots if that would be any help?) And found nothing wrong!

So, they did a hard reset (disconnected battery). That immediately adjusted the digital range from 110 to 210 miles, a huge increase but still 100+ miles below normal. Remember 167 is the digital range gauge max when tank is full. So, they had me drive fifty miles on a freeway for an MPG check. Averaged 28 MPG at 65 MPH on cruise control which is the EPA highway rating for the Scion xB! Another shocking result is that still doesn't explain the overall lousy MPG even when you factor out the excessive idling.

It will be interesting to see when the tank needs refilling in a few days, what the digital range gauge resets to:

167? Current Normal
210? Mechanics Adjustment Today
3XX? Normal

Your thoughts?
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Wednesday, July 13th, 2022 AT 3:01 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

That is an interesting one. First, thanks for the update. However, I'm interested in seeing if it improves.

The idea of a hard reset normally won't improve fuel mileage. However, if it worked, that's great.

Let me know if things do go back to normal. I'm interested in knowing.

Take care,

Joe
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Wednesday, July 13th, 2022 AT 9:33 PM

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