Huge change in fuel consumption?

Tiny
JGWJ5800
  • MEMBER
  • 1 POST
  • 2007 FORD F-150
  • V8
  • 4WD
  • AUTOMATIC
  • 28,000 MILES
I own a 2007 f-150 5.4 triton v 8 I have 28000 mile tires are inflated correctly and all the little stuff is taken care of ie oil change ect. Ihave seen a reduction in mpg a slight miss at idle and sometime the oder of gas while at idle. I use to get 17mpg in town and 21.5 on hwy now 11mpg in town and 17 on hwy. Thanks jim
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Thursday, September 3rd, 2020 AT 2:20 PM (Merged)
Tiny
MJR346
  • MECHANIC
  • 132 POSTS
Usually unless the check engine light is on, I wouldn't suspect a engine issue. Could be a fuel issue with many areas going to 10% ethanol or more and that is known to drop mileage hard
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+1
Thursday, September 3rd, 2020 AT 2:20 PM (Merged)
Tiny
MIKE H R
  • MECHANIC
  • 3,094 POSTS
There also may be some buildup of carbon in the throttle body clogging a air vent. If this is the case to clean it out Use some throttle body cleaner and try that. Available at most aiutomotive stores. Follow instruction when using it.
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Thursday, September 3rd, 2020 AT 2:20 PM (Merged)
Tiny
5123321055
  • MEMBER
  • 16 POSTS
  • 2002 FORD F-150
  • 5.4L
  • V8
  • 2WD
  • AUTOMATIC
  • 170,000 MILES
There are no codes. I did a live data read on the 02 sensors and Bank 1 and 2 upstream have fluctuating readings with a square up and down sign wave but Bank 1 and 2 downstream are reading 0.000. I would think 0 reading would show a check engine light are is this reading normal? I have 170,000 on the original 02 sensors so was thinking it might be time to replace.
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Thursday, September 3rd, 2020 AT 2:21 PM (Merged)
Tiny
5123321055
  • MEMBER
  • 16 POSTS
Additional information: I drove around with live data and both bank 2's started giving readings. The sign waves where all over the place and at times flat lined.
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Thursday, September 3rd, 2020 AT 2:21 PM (Merged)
Tiny
MASTERWRENCH
  • MECHANIC
  • 258 POSTS
A voltage reading of 0.00 on both downstream sensors is not what I would expect to see. Under normal conditions, the downstream will be a very close mirror image of the upstream just after the engine is started. After the engine runs for a short period of time and the catalytic converters have time to "light off", the downstream signal will begin to level off. An absolute reading of 0.00v is very unlikely and is very possible the result of worn sensors.

In your second post, you indicate "both bank 2's started giving readings". Do you mean both downstream sensors or the upstream and downstream on Bank 2?
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Thursday, September 3rd, 2020 AT 2:21 PM (Merged)
Tiny
5123321055
  • MEMBER
  • 16 POSTS
Both downstream sensors started responding.
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Thursday, September 3rd, 2020 AT 2:21 PM (Merged)
Tiny
MASTERWRENCH
  • MECHANIC
  • 258 POSTS
Okay, I'm with you. It's probably working normally then. You are correct, if there really was an issue(like both sensors unexpectedly stuck at 0.00v) it would definitely set a code. Are you sure your fuel economy drop off isn't just a result of the cooler temps and the seasonal switch to winter blend fuel? Have you changed anything on the vehicle recently such as a more aggressive tire tread or oversize tire? Some of those things can have a more significant effect on economy than some realize.
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Thursday, September 3rd, 2020 AT 2:21 PM (Merged)
Tiny
5123321055
  • MEMBER
  • 16 POSTS
Haven't changed anything, truck is stock. The mileage drop off has been last 4-5 months. I was reading where 02's can become lazy and not throw a code causing a drop in fuel economy and with 170,000 miles on original 02's I thought it might be something to look into. The truck has been very well maintained.
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Thursday, September 3rd, 2020 AT 2:21 PM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,554 POSTS
Hello,

If I can help out. I have seen the MAF sensor go bad causing this issue which will cause the O2 issue as well. I would replace the sensor with a new unit these are normal service items. Here is a guide to help walk you through the steps with instructions in the diagrams below to show you on your car:

https://www.2carpros.com/articles/how-to-replace-a-mass-air-flow-sensor-maf

Mass Air Flow Sensor - YC2Z12B579BARM $264.51

Check out the diagrams (below). Please let us know what happens.
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Thursday, September 3rd, 2020 AT 2:21 PM (Merged)
Tiny
5123321055
  • MEMBER
  • 16 POSTS
Thank you for the response, looking into to doing that.
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Thursday, September 3rd, 2020 AT 2:21 PM (Merged)
Tiny
NORDMEER
  • MEMBER
  • 2 POSTS
  • 2002 FORD F-150
2002 F-150 4x4 Super Cab 4.6L V8
53,000 mi
Auto Trans
Tires 265 75 16 (Originals 245 75 16)

Bought the truck used through a non-Ford dealer and also purchased a warranty plan from the same dealer. The head leaked in January, and the dealer replaced the gasket. In March, it started to leak again, and they told me this time that the cylinder head itself was gone. They then installed a new head. Now the truck is low on power, and fuel consumption is up by 25%. On the highway, the tranny often shifts itself back into 2nd gear just to keep 65mi/hr on the hills. It was never like this before. I brought it back and they are now telling me that the problem is with the tires, that they're too big. They also said the truck needs to be "recalibrated" for the tire size. But its only one size (as stated above) and I had this tire size on the truck since last fall, and also the winter before, with no problems. Any ideas or suggestions are greatly appreciated. Thanks.
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Thursday, September 3rd, 2020 AT 2:21 PM (Merged)
Tiny
2CARPRO JACK
  • MECHANIC
  • 11,533 POSTS
Has it set the check engine light? Sounds like they are trying to push it off on you. Take it back to them and demand that it be fixed correctly. That littel of a tire change wont kill hardly any power, just change the shift points.
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Thursday, September 3rd, 2020 AT 2:21 PM (Merged)
Tiny
NORDMEER
  • MEMBER
  • 2 POSTS
Thanks for the reply. Went back to challenge the dealer, and they finally gave in and sent the truck to Ford. Turns out 2 cylinders on the right side (same side as the new cylinder head) are 6% low on compression. Looks like I have a legit case. Again, appreciate the second opinion 2CarPro Jack!
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Thursday, September 3rd, 2020 AT 2:21 PM (Merged)
Tiny
2CARPRO JACK
  • MECHANIC
  • 11,533 POSTS
Your welcome
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Thursday, September 3rd, 2020 AT 2:21 PM (Merged)

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