Poor gas mileage

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

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.

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

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.

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

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.

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

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?

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.

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

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.

Attached is the AutoZone scan showing no issues. It's not a Live Data Scan and suggested I go to a mechanic for that.

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

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

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

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

Yep, just push a few buttons or something to that affect and it would reset / reprogram the software.

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.

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?

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

So, if I am averaging 28 MPG for 50 miles of highway driving and replicate that for an entire tank of 14 gallons, that would be 392 miles! That seems impossible now but the math adds up?

The other interesting observation was that the street miles for this MPG test were 46 miles on the odometer, but the digital range readout only decreased by 23 miles which is exactly half. Can you explain that?

Hi,

That is an interesting one. I don't know why it would be half. That doesn't even make sense.

Joe

So, I filled up my tank for the first time since the hard reset and the digital range gauge got to 225 miles. Prior to that it's always been 167 miles. So, it added 58 miles. Not sure if that's an aberration or permanent. Several months ago, I had 200+ digital range after gassing up but every fill up after that it went back to 167.

Hi,

That is good news. Hopefully, it won't change. If it does, let me know and we'll try again. LOL

You take care of yourself and feel free to come back anytime in the future.

Joe

Today I filled up for the second time since the Hard Reset and digital range reverted back to 167 miles. So, the 225-mile digital range after the first fill up was an aberration. Would I need to Hard Reset after each fill up to get the extra range?

Also, I drove 126 miles based on the odometer but only 97 based on the digital range gauge! There were some brief idling but nowhere near enough to account for the 29-mile difference. Driving was approximately 70% city + 30% highway. Can you explain the variance?

I will have an average MPG figure tomorrow when I fill up.

Hi,

As far as the variance, that is tough because they get the information from the same module. If anything, I would suspect the range indicator is bad.

Just for the heck of it, have someone drive a different vehicle from point A to point B and clock the miles. You do the same to determine which one is accurate, the range gauge or the odometer.

Also, let me know the actual mileage you got.

Take care,

Joe

Yesterday I averaged 13 MPG from a combined work driving and many hours of idling.

Today I averaged 22 MPG from work only, comprised mostly of city driving and multiple brief periods of idling. My car's EPA MPG ratings are 27 Hwy / 22 City so it's consistent. Had I done this type of driving until an empty tank of 14 gallons, I would have traveled 308 miles and I haven't had that type of range for many months! So, I'm skeptical I would run out of gas long before that! This is encouraging but still leaves me baffled as to why that MPG average is normal, but the overall range is still way down?

What's strange is that with the last 2 fill ups, the digital range gauge reset to 167 miles just like it's been throughout this ordeal except for that 225 mile aberration after the Hard Reset. Then in the middle of my route, the range gauge abruptly went up another maybe 40 to 60 miles as I didn't notice it right away.

The increase in the range gauge is likely because the driving style increased the average MPG.

I have a crazy question. Are the tires all the original equipment size? The mileage variance is driving me crazy. LOL

Let me know,

Joe

It is interesting that the digital range would adapt as if I were to take a long trip with mostly freeway driving, it would auto adjust towards the predicted 27 MPG / EPA rating. Perhaps the Hard Reset partially erased the memory of all the idling? For if it erased all the idling, it would go to 300+. I wonder if multiple consecutive Hard Resets would get it back to 300+?

I was also going to check how many gallons of gas are burned just idling the car continuously for many hours, filling up the tank right before and filling up again right after. Do you think this would reveal anything? I've checked several times and I lose about ~ 4 miles of digital range per hour of idling but I'm not sure how that translates to gallons burned.

The tires are all stock size and all four were replaced two weeks ago with all-season tires replacing a very worn set of snow tires which might help mileage slightly as snow tires are made of softer rubber and might decrease rolling resistance.

Do you think a road trip to Las Vegas and back from Phoenix would help?

Hi,

I think any long trip is a good thing. The worst thing you can do to a vehicle is not drive it. Running it keeps things lubricated and working properly.

As far as the hard reset is concerned, that's a good question. It wouldn't hurt to try. Also, if you reset the range gauge, what happens now?

Joe