poor gas mileage and acceleration

2012 FORD F-150

85,000 MILES • 5.0L • V8 • 4WD • AUTOMATIC

DGREGORY70

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Hi, I've been getting poor gas mileage and acceleration for awhile now. Based on the gas mileage displayed on the dash I used to get 17 city and 19 or 20 highway. My son used to race go karts and I would have the whole family and a small trailer and still get at least 17 on the highway and about 15 if I took the back way home on secondary stop and go roads. Now I can't get past 15-15.5 anywhere really. I used to play around and reset the trip computer on the highway and see how high the instantaneous mileage would go, usually I could get about 23 until I exited. I tried it to day and it never went higher than 18.5 and ended up at 16.5 when I exited. This was cruising around 70 MPH at 1,800 RPMs. It also doesn't accelerate very well. It doesn't stumble, it just feels like I have a big truck and a small engine. IT wasn't this bad pulling the trailer. It doesn't really accelerate well until about 2,500 RPMs and then it feels better, but not great.

I've replaced the MAF sensor, spark plugs and just installed a new K&N filter. no improvement. I've also cleaned the throttle body, checked the temperature readings on the Cat's sprayed brake cleaner and carb cleaner around the vacuum lines I could see while it was running to check for vacuum leaks and nothing. I've also checked the temps on the rotors after driving and they seem okay as well. I have a older scan tool and have checked what I could based on web research and nothing seems to stand out. It's also never thrown any codes. I have mechanics check it but not in the last 2 years and they just tell me everything fine, but I don't know if they've test drove it or just hooked it up to the computer.

Anything you can think of or recommend would be appreciated. It's driving me crazy, but the trucks paid for and really clean still, but I'm going to be pulling a boat later this summer and I'm afraid of how it's going to react now with a trailer.

Thank you

Jun 10, 2021 at 1:56 PM

KASEKENNY

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There could be a couple other reasons for this and we need to start with revving the engine and look for black smoke. You may not have much but we need to start with this as I suspect you have some injectors starting to leak too much fuel.

https://www.2carpros.com/articles/engine-black-smoke

Next we need to use that scan tool and monitor the o2 sensor data when you are driving down the highway.

There is a chance you have a faulty o2 sensor and that is not telling the PCM that it is over fueling so it continues to dump too much fuel.

We need to see what the voltages are or your short term fuel trims.

Next we need to see what the old spark plugs looked like. Did they show signs of fouling?

Below are a couple charts that will help with this. Please let us know what questions you have, then what you find. Thanks

Images (Click to enlarge)

Jun 11, 2021 at 6:20 PM

DGREGORY70

MEMBER
46 POSTS

Okay, I’ll take a look at those things tomorrow and let you know what I find. I changed the plugs awhile ago and I think they’re gone, but I did take some pictures which I’ve included for you to look at. For some reason I only have 7, but they were all very similar. Tell me if you see anything, I always have a hard time reading them. It always seems like it could fall into several categories.

Images (Click to enlarge)

Jun 11, 2021 at 7:16 PM

DGREGORY70

MEMBER
46 POSTS

I've got 3 videos for you here, I'm not sure if I've got the readings you want to look at or not. If not let me know and I'll go back out. I also apologize in advance for the quality of the 2nd video, my 12 year old was holding the camera because I thought that would be better than me doing it while driving and it didn't quite work out that way.

The 1st video was me accelerating onto the highway this morning after about a 5 minute drive.

The second video was me entering the highway again but with different measurements on the screen.

The last video was me cruising on the highway after the second vide, with a different set of readings. Hopefully one of these helps.

Videos (Click to enlarge)

Jun 12, 2021 at 12:21 PM

KASEKENNY

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The numbers are not out of line. However, the last three spark plugs that you had pictures of appear to be carbon fouled. Do you know which cylinders these came out of?

I would think about changing the injectors out of these cylinders. Clearly anytime we are dealing with fuel mileage it is very subjective to the amount of hard accelerating you do but if you have been driving the same the whole time then I am thinking you have an injector or two leaking.

The only other possible cause would be o2 sensor issues. However, they appear to be operating properly.

Jun 13, 2021 at 8:32 PM

DGREGORY70

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46 POSTS

Yeah, the driving is pretty much the same, especially just cruis8ng down the freeway. I’ll have to look and see if I still have the info for the spark plugs. Would the injectors account for sluggish acceleration?

Jun 14, 2021 at 5:15 AM

KASEKENNY

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Yes. The injectors over fueling will throw off the fuel mixture but I was hoping to see this in the o2 sensor data. However the plugs are showing it so I would check the fuel pressure and then let it sit with the gauge on it and see how long it takes to bleed off.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Jun 14, 2021 at 6:54 AM

DGREGORY70

MEMBER
46 POSTS

Hi, I'm back again. I don't have any black smoke from my exhaust if I hit the throttle, just some white and grey. I was going to check the fuel pressure but my truck doesn't have a test port and I got a little concerned about testing it without. Anyway I finally got my boat this last week and it is horrible trailering it. It feels like it has nothing go uphill or when starting from a stop. I used to have a 6 cylinder Fi50 and we pulled a small 10' cargo trailer and it felt like it was working pretty hard. When I got this truck it pulled that trailer along with the whole family and it didn't feel like anything was back there. With the boat it now feels like I have the 6 cylinder again. So I put the scan tool on it again today and had my wife with me and saw something I wanted to ask you about.

Looking at the O2 sensor data, the bank 1 and 2, sensor 2 data seem to be similar when cruising , but if I accelerate or vary the throttle they become very different. they can be reading .7 on one and .2 on the other and one might be changing more rapidly than the other. but I'm not sure just looking at the tool and the one I have doesn't graph. I think I can get one that does if you think this might be the issue. when things get back to cruise or consistent throttle they tend to read the same. The sensor 1 data seems to be closer together I think.

I have some video my wife took of the scan tool but she wasn't real steady and I'm almost embarrassed to send it to you. You almost need to look at it in slow mo to see what's happening.

Could this be the problem causing my issue, even without a CEL? IF it might be I can have my son take better video and send that too you or anything else.

Let me know what you think.

Thanks

Jul 17, 2021 at 11:41 AM

KASEKENNY

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That is great info. Which bank has the higher o2 reading when you are accelerating?

I understand that you don't have black smoke but gray smoke is indicating the same thing. The smoke will only get darker the worse the injectors get.

No matter what you have a rich condition now the key is finding what is causing it. It could be a faulty sensor causing the PCM to over fuel the engine or it could just be a leaking injector.

The goo thing is you seem to have one bank running properly and the other is not. This means we can verify what the issue is by switching components one at a time from one side to the other to find when the other bank starts running rich just like this current bank is.

I would suggest starting the o2 sensors. Swap them all from one side to the other. I don't think that is the issue but they are the easiest thing and could be doing it so I would swap them just to eliminate them for sure.

The fact that this is only affecting one bank, it is unlikely that it is a MAF sensor or vacuum leak as that would effects both banks.

If the o2 sensor is not the issue then I would swap the injectors side to side.

I included the process below for this. Please let us know what you find with this.

Images (Click to enlarge)

Jul 19, 2021 at 8:27 AM

DGREGORY70

MEMBER
46 POSTS

Okay. So you feel mor confident it’s the injectors then? That the O2 sensors probably aren’t the issue?

I going to borrow a better scanner that I think graphs so I can get a better idea of which sensor may be the issue.

As far as the injectors, I’ve never messed with them before. And it’s a little intimidating, although videos online make it look like changing plugs and depressurizing the fuel system. Is there anything I need to watch out for or that’s easy to screw up? My buddy posted a meme a year or so ago that said “every 20 minute job is just a busted screw away from a 3 day ordeal”. Anyway let me know what you think and I’ll try to get better readings and swap the sensors.

Thanks

Jul 20, 2021 at 10:15 AM

KASEKENNY

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This can be a big deal if you are not familiar but not impossible. I am attaching the process from the manual on how to depressurize the fuel system. Also, if you are still worried just wrap a rag around the connection that you are taking apart as you pull it apart and that will keep any fuel spray down. However, if the pressure is relieved then you are good.

Images (Click to enlarge)

Jul 20, 2021 at 8:12 PM

DGREGORY70

MEMBER
46 POSTS

I wasn’t able to get any physical work done this weekend, but I did get the other scan tool and was wondering if you could look at these 2 videos and let me know if they tell you anything. Things are moving so quick that it’s hard for me to tell what’s actually happening because I’m not sure how they should react normally. One is definitely moving faster than the other, I just don’t know if the slow one is lazy or the fast one is incorrect. They were both taken while accelerating. The strange thing is that when I had my wife take video while hauling the boat, they didn’t seem as bad.

Also, I was thinking about it, it’d always seemed that the truck felt better in the morning when I first get going. These sensors are the downstream sensors correct? So they don’t have any input until the vehicle warms up correct? Is that another clue? Does that make sense?

Thanks again

Video (Click to enlarge)

Jul 26, 2021 at 5:27 AM

DGREGORY70

MEMBER
46 POSTS

Here’s the second video. Also this scan tool will graph, it just won’t graph them both together so I don’t know if that would help you or not.

Video (Click to enlarge)

Jul 26, 2021 at 5:28 AM

KASEKENNY

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Unfortunately those numbers appear to be perfect. Both high and low are switching around 0 but are dropping high to low which means that the PCM is seeing a rich condition and it adjusts, then adjusts again. Basically it is never going to be sitting still when operating properly. When they are not switching or jumping around is when there is an issue. That means that the exhaust is rich or lean and the PCM is not able to adjust it by adding or removing fuel.

Just to take a step back, were these numbers when the engine was not running properly?

Also, what were all the tempeature sensors reading? Engine coolant, ambient, and intake air temperature.

You are correct that the o2 sensor data is ignored until it is warmed up so if this was before the engine warmed up then that may explain why they look okay.

Jul 26, 2021 at 6:51 PM

DGREGORY70

MEMBER
46 POSTS

So yes these were taken when the engine wasn’t performing properly, which is basically all of the time. It feels better after it’s first started in the morning but then it seems to get worse. There’s just no get up and go in the lower RPM’s and it’s shifting at higher RPM’s.

When I was looking at those numbers what I saw was that sensor 1 on both banks seemed to stay pretty close together as they adjusted. Sensor 2 adjusted fairly differently on each bank. One seemed to adjust very quickly and the other much slower. I know it’s hard to catch on the video, that’s why I was hoping that they could be graphed together. But if you slow the video and step through you can see where one may be at .675 and the other at .158. Was that not correct or didn’t it matter?

I’ll do it again and get the additional data you asked for.

Jul 27, 2021 at 5:13 AM

KASEKENNY

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I understand what you are saying. However, that is not abnormal. Basically the down stream o2 sensors are measuring the ability of the converter to reduce the harmful emissions and they are going to work differently from each other. As long as they are both switching numbers and not remaining steady then that shows they are operating.

Based on this info, I think we can move on from o2 sensors but we need to check compression next as that can definitely cause what you are seeing.

Also, here are some guides that cover this low power issue which is what we have here:

https://www.2carpros.com/articles/engine-has-low-power-output

https://www.2carpros.com/articles/symptoms-of-low-engine-power

Here is a guide that will show how to test compression:

https://www.2carpros.com/articles/how-to-test-engine-compression

Let me know what you find with this. Thanks

Jul 27, 2021 at 6:57 PM