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Lack of power on the low end?

Tiny
DGREGORY70
  • MEMBER
  • 2012 FORD F-150
  • 5.0L
  • V8
  • 4WD
  • AUTOMATIC
  • 81,000 MILES
I've been working on this issue on this site for awhile and I don't know what happened but it looks like my question got merged with several others and I can no longer reply so I'm starting another thread.

This truck feels like it's lost power and accelerates poorly, especially at lower RPM's. Gas mileage also down about 2 MPG and it seems like it even cruises on the freeway at a higher RPM and with worse gas mileage, at least according to the instant mileage on the dash. The other strange thing is that it seems much better early in the morning when I first start it and the longer it runs the worse it seems. Dealership has checked it a couple times and says everything is as it should be and it's never thrown any codes.

I've replaced the MAF sensor and the spark plugs, I've checked for vacuum leaks with carb cleaner while the engine was running and couldn't find anything. The last thing I was supposed to check was the catalytic converter but hadn't gotten around to getting an infrared thermometer, but I noticed on my scan tool there are 2 readings (see first picture) which I assume are the intake and exhaust temperatures which are almost identical, so it's not the cat then correct?

I disconnected the battery and pulled the throttle body yesterday to clean it. It didn't really seem dirty but after I reinstalled it, the truck seemed to run much better. But this is the same thing that happened after changing the MAF. It seems great initially but then relearns all of it's bad habits and the good feeling doesn't last very long.

Any other things I can check with my older consumer scan tool? I'm going to be towing in the summer and if there's a problem I'd really like to get it resolved before then.
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Tuesday, December 15th, 2020 AT 3:30 PM

13 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,747 POSTS
Hi,

I think I was working with you. As far as the catalytic converter temperatures, yes, there are two. See pic 1. Also, the temp shown on the scan tool is low. For a catalytic converter to operate normally, it should be between 400° F and 600° F.

I noticed the scanner offers live data. Can you let me know what the short term fuel trims are? The will be listed as STFT.

Let me know.

Joe
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Monday, June 28th, 2021 AT 12:40 PM
Tiny
DGREGORY70
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  • 46 POSTS
Yeah, I’m an idiot, when I quickly glanced under the truck yesterday, I only saw the one catalytic converter, the other one kind of hides behind the frame. So those readings don’t tell me if they’re clogged or not then. The temperatures were low because I took that after a real short drive yesterday to show you the readings. But the 400-600 you quoted has me concerned because I swear after a long drive yesterday while I was watching those temperatures were in the 800-1000 range.
I’ve attached a picture of the fuel trim readings below. That was taken idealist in my drive after a short ride home this afternoon.
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Monday, June 28th, 2021 AT 12:40 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,747 POSTS
Hi,

The fuel trims look good. As far as the temp, 400 to 600 is where it truly starts working. What you saw is normal. Actually, they can reach up to 1600°F.

Here is a link that explains how to check a catalytic converter. See if it helps.

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

Let me know.

Joe
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Monday, June 28th, 2021 AT 12:40 PM
Tiny
DGREGORY70
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  • 46 POSTS
Okay, so I’m just going to have to get a thermometer to check the catalytic converter’s then. I’ll let you know what I find. A question though after reading the article. The throttle snap back test with a vacuum gauge. Just to get an idea, does the fuel economy reading on the dash tell you the same thing? Isn’t that a glorified vacuum reading or is that just the old analog fuel economy gauges from way back?
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Monday, June 28th, 2021 AT 12:40 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

As far as the vacuum, no this system it is designed that way. It uses signals from speed sensors, throttle position, and so on to determine the MPG.

Let me know what you find.

Joe
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Monday, June 28th, 2021 AT 12:40 PM
Tiny
DGREGORY70
  • MEMBER
  • 46 POSTS
Hi, so I was able to get a thermometer and finally checked the catalytic converter’s. After a short drive home from work the scan tool said the catalytic converter sensors were about 640 degrees. With the thermometer these are the readings I got on each catalytic converter with the engine running.

Driver side 308 incoming 340 exhaust.
Passenger side 312 incoming 350 exhaust.

So based on these readings and the guide you sent me the catalytic converter’s are working okay then? If that's the case what else can I check?

Thanks
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Monday, June 28th, 2021 AT 12:40 PM
Tiny
JACOBANDNICKOLAS
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The temperatures seem normal. When power loss and a decrease in MPG occur, the first things I look at are the catalytic converters, which you have done, fuel pressure, the need for a tune up, and even a coolant temperature sensor.

Since the fuel trims are in line, that eliminates fuel pressure and likely the coolant temperature sensor. You have eliminated the catalytic converters and tune up. Is there any drag on the vehicle when driving? Also, are there any smells or sounds you can think of that may help me?

Let me know.

Joe
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Monday, June 28th, 2021 AT 12:40 PM
Tiny
DGREGORY70
  • MEMBER
  • 46 POSTS
I don't believe there's any drag on the vehicle. The only thing I could think of would be the brakes and I just replaced the front pads and rotors because they were worn. The rear are still good according to the dealership and their last complimentary inspection. As for sounds, nothing I could describe or put into any context. I mean everything sounds a little louder than when it was new and it sounds and feels like there's a little more work being done under the floor near the transmission tunnel but I could be reaching.

I guess the big thing that sticks in my mind is that I used to show on average 17mpg on the dash and it's now around 15.5 and it's been a gradual decrease. It also seems like its working harder even cruising on the freeway. I used to play around on road trips with the gas mileage from the trip odometer to see how high I could get it. I would reset it on the freeway and I would cruise around 70 MPG at about 1,700 RPM's and get 20-23 MPG. If I try that now the best I can do is about 19.5 and the RPM's are around 1,900 most of the time.

Would it help If I took a video of the dash while accelerating? Can you get anything from that? If so when or where should I do it? Should I hammer it getting on the freeway or a normal takeoff from a light to about 55 MPH?

Let me know.
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Monday, June 28th, 2021 AT 12:40 PM
Tiny
JACOBANDNICKOLAS
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Hi,

A video wouldn't hurt. As far as driving, I would suggest doing it under normal conditions. Since the front brakes were replaced, I wonder if there is an issue with them dragging. Did you replace them? If you did, were they worn evenly?

Just for the heck of it do this. After driving for a few miles, when you park, get out and see if there is excessive heat coming from any of the wheels that may indicate a hung up caliper or other issue causing it to drag.

Let me know.

Joe
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Monday, June 28th, 2021 AT 12:40 PM
Tiny
DGREGORY70
  • MEMBER
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I've attached 2 videos. I'm not sure how much they'll help. The first one is kind of a normal start. The second one was a little more throttle cause I had to cross a busy intersection and then at the end I was costing down a hill.

As for the brakes, I replaced them and I didn't see anything odd, but I didn't really study them either. They had been on there a long time and I knew they were about done. I did check the rotors today with the infrared thermometer I bought for the cat's. IT was about 34 degrees outside and both front rotors were around 99deg and the rears were both 75-77 degrees.
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Monday, June 28th, 2021 AT 12:40 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,747 POSTS
Hi,

It's really hard to tell by the video. You know, I reread everything we talked about and something stood out. You indicated the RPM's are higher than they were prior to the issue. Can you tell if it is shifting into overdrive?

Let me know.
Joe
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Monday, June 28th, 2021 AT 12:40 PM
Tiny
DGREGORY70
  • MEMBER
  • 46 POSTS
Too shaky or too fast acceleration on the video or just not enough information?

Overdrive is just 6th gear correct? If so then yes it shifts into 6th according to the dash.
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Monday, June 28th, 2021 AT 12:40 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

It is just hard to see what is happening on the video. Hope you understand. As far as the transmission, according to the manual, it had OD. When driving it, see if you can feel it engage after the last gear. If it doesn't, that could be why you have lower fuel mileage and higher RPM's when driving.

Joe
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Monday, June 28th, 2021 AT 12:40 PM

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