Terrible Gas Mileage on 2013 V6 Mustang

headhunter07

Member
Jun 2, 2020
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19
Dubai
So here's a bit of backstory: I bought a used automatic 2013 base V6 Mustang with 100,000 miles on it a few days back. The main reason I went the V6 route is because my commute is around 70 miles daily(hwy+city) and I'm a student, so mileage matters a lot for me.

So far, I've driven the car in the city(stop & go lights, small roads with constant stops) & I've got 7MPG!!!(30l/100km). I'm sure this is accurate as I calculated the distance myself & measured the fuel readings. This is way off from the advertised 19mpg city(12.4/100km). This is insane because I've hardly driven 60 miles(100km) and my tank is half empty. Also, the MPG free-falls in idle, from 7MPG to as low as 5MPG. Highest I've seen is 9MPG.

I have not driven the car with a heavy foot, apart from maybe gunning it 2-3 times at stoplight to satisfy my initial excitement of getting my first car. I'm pretty confident that my driving is not the cause for terrible mileage. Had no real chance to take it to a highway yet because of the Covid19 curfew around my city.

The previous history of the car shows it was damaged in a front-end collision that was later repaired(i was aware of this). I bought it off an auction lot so I have no real history of maintenance from the previous owner. The engine, gear, chassis are all in good condition as verified by a mechanic.

What are my first steps to trouble shoot? Should I get an OBD scanner, replace the spark plugs and O2 sensor? Or, wait till I get a chance to drive it on the highway or a road-trip to see if the mileage improves? Apologies if all of this sounds like too much, I'm just paranoid and anxiety struck from the fear of having to maintain a financial burden if this contunies. I'm just 19.

Also, the car has been sitting for a while at the lot. All I did was flush trans fluid, new brake fluids & engine oil. 17 inch tyres all round.
Also, I checked for any gassy smell around the car & exhaust, I can smell a bit of gas at the tips of the exhaust when running but nothing too extraordinarily bad. A little bit rough at idle when I stop and go. No black smoke or soot on the exhaust tips. Car may be running rich, any way to confirm? And where do I start troubleshooting?

Any help will be appreciated, thanks!
 
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EmmJay

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Jun 16, 2019
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The first thing to do is pull any trouble codes and see what shows up. My guess is this will point you in the right direction. Don't start throwing parts at it until you track down the exact problem. For example, just because you might have a code for a bad O2 sensor reading doesn't mean the O2 sensor is bad. It could be some other part elsewhere in the fuel system is causing the code fault. With mileage that low I think you would see the engine not running well. You probably shouldn't drive it to much until you fix the problem. Running very rich might damage the catalytic convertors. Especially as highway speeds for over 10-15 minutes.

As for what OBD scanner to buy I suggest one of the following:
View: https://www.amazon.com/ScanTool-OBDLink-Bluetooth-Professional-Diagnostics/dp/B006NZTZLQ/ref=sr_1_2?dchild=1&keywords=OBDLink+mx&qid=1591150592&s=automotive&sr=1-2
View: https://www.amazon.com/gp/product/B081VQVD3F/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1


They work well with a very powerful scanning software called Forscan. This software will allow you to monitor data real time and see where an issues might be. Once you get the codes come back here and post them to get more precise advice.
 
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David Young

Active Member
Sep 16, 2012
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I would start off cleaning your throttle body with throttle body spray cleaner. Lots of youtube videos on how to do it yourself. 7 miles per gallon, I would be looking for a fuel leak. I get 20-21 in town gas mileage with an automatic with 3.73 gears :)
 
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headhunter07

Member
Jun 2, 2020
6
1
13
19
Dubai
@EmmJay Thank you for this! I just ordered an OBD Scanner. Did a bit of research on how to see if my O2 sensors are reading right, also the short and long trim fuel readings - this will help me diagnose my running rich situation. I'm also looking for a fuel or vacuum leak.
I will have it delivered over the weekend & come back with my findings.

@David Young
Surprising enough, the throttle body is clean of any gunk & the engine gives good throttle response. I also cleaned out the air filters.
I will change out the spark plugs to eliminate that problem and considering the car has 100k miles, they usually wear out by then.

I'm looking to order the plugs online. Do you know what the OEM gap size is for 11-14 V6's?
 

EmmJay

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One thing to note is that a vacuum leak will almost always cause the engine to run lean not rich.
 

headhunter07

Member
Jun 2, 2020
6
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19
Dubai
So, I was able to get my hand on the OBD scanner & ran a diagnostic test on the car. For some reason, I was not able to get live readings on the front Bank 1 sensor 1 & Bank 2 sensor 1. Here are the codes I got:

1.
P2254(00)
Raw code: 225400
ECU: Engine control unit
Status: Test failed since last DTC clear
OBDII: Heated oxygen sensor (HO2S) 1, bank 2, negative current control - open circuit

2.
P2251(00)
Raw code: 225100
ECU: Engine control unit
Status: Test failed since last DTC clear
OBDII: Heated oxygen sensor (HO2S) 1, bank 1, negative current control - open circuit

3.
P0050(00)
Raw code: 005000
ECU: Engine control unit
Status: Pending, Test failed since last DTC clear
OBDII: Heated oxygen sensor (HO2S) 1, bank 2, heater control - circuit malfunction

4.
P0030(00)
Raw code: 003000
ECU: Engine control unit
Status: Test failed since last DTC clear
OBDII: Heated oxygen sensor (HO2S) 1, bank 1, heater control - circuit malfunction

5.
P0050
Raw code: 0050
ECU: Engine control unit
Status: Pending
OBDII: Heated oxygen sensor (HO2S) 1, bank 2, heater control - circuit malfunction
(I used two different apps for scanning, one of them(Torque) only gave me this code and not the above 1-4.)

Also, there were these 2 codes which were shown as "Historic Faults":

1.
P0455
Raw code: 0455
ECU: Engine control unit
Status: Permanent
OBDII: Evaporative emission (EVAP) system - large leak detected
Ford: Evap Emission Control System Leak Detected (Gross Leak/No Flow)

2.
P0457
Raw code: 0457
ECU: Engine control unit
Status: Permanent
OBDII: Evaporative emission (EVAP) system - leak detected (filler cap loose/off)


Pretty bummed cause I didn't see all of this coming, but where do I go from here?
 

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headhunter07

Member
Jun 2, 2020
6
1
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19
Dubai
Hey guys..a little bit of an update:

I tried multiple scanner apps & installing the right Ford PID's, still no luck on getting live O2 data from either of the upstream sensors.
Down stream sensors are working well & are steady - so the CAT's are fine.

I cleared the codes & re-scanned the car and this time around, no O2 related codes, just the EVAP ones.
Heater Monitor modules for all sensors are functioning properly.

Can I go ahead and replace the upstream O2 sensors without hesitation or is there further diagnosing to be done? Any help will be appreciated!
 

headhunter07

Member
Jun 2, 2020
6
1
13
19
Dubai
After clearing the codes did you drive the car some to see if they returned?
I let the car idle for about 30 mins & got it warmed up till it mentioned it was in a "closed loop" meaning the ECU was taking information from the sensors. Still no live data though..


I'm not sure if test "failed since last DTC" clear means the component itself failed or it wasn't ready for the test. Unable to find more on it online
 

EmmJay

Member
Jun 16, 2019
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It sounds like it might be the code that trips until the car goes through a proper drive cycle before an emissions test can be done. I ran into this problem with my 2007 Mustang due to the aftermarket tune turning off the post convertor O2 sensors. It never read all the O2 sensors properly to allow the drive cycle to complete so the code to clear for testing to be removed.
 

mikestang63

SN Certified Technician
Aug 27, 2012
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In the garage
disconnect the battery for 30 minutes. I have seen where the MPG counter if not reset/cleared after a while gets wonky. Also, throw a bottle of techron in the tank and clean the Throttle body.
 
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