Huge change in fuel consumption?

A few culprits for the change in fuel consumption could be; a leak in the exhaust near O2 sensor, a bad O2 sensor, catyltic converter needs replacement, needs general tune-up, ECU or sensor malfunction but 9 times out of ten it will be the MAF sensor

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

There are other things that aren't always part of general maintenance that can really affect fuel mileage such as dirty fuel injectors. Most injector cleaners do not do very much and are not capable of making partially clogged injectors free of deposits.

The fact that fuel consumption does not change in a, "not towing" situation is interesting. That makes me think more along the lines of a clogged converter or bad O2 sensor. I say this because they are things that get taxed when towing because they are dealing with more un-burnt fuel which makes them hotter than usual and can lead to failure.
Fords can sometimes take a little while for the computer to adjust when the load demand is different.

How long does your truck continue to have bad gas mileage after you stop towing?

Let me know and I will try to help.

That is the right way to check fuel consumption.
With electrical system stuff, a warning light, especially in this situation, might not get lit. Even when a code reader is hooked up or you can sometimes use a shunt wire to pull codes, they don't always show up.
If the computer gets a signal from the O2 sensor that the mixture is lean, it will feed the system more gas. Even though the sensor has malfunctioned, the computer will not see it as a malfunction if it falls within a certain range. An exhaust leak will cause a lean condition and do the same thing. The O2 sensor might have failed and it is stuck at a certain voltage requesting the same amount of gas from the computer as when you were towing. I am mentioning this because I am thinking something is failing or failed while you were towing and got stuck to where it can no longer sense variations in mixture or load on the motor and it is sending the same signal to the computer.

I do not know everything. I am not sure that an O2 sensor can get stuck at a certain voltage and then continue to send that same signal creating your problem. From the O2 sensors I have some knowledge of, I believe it is possible.

Electrical problems are a process of elimination thing and you do sometimes have to buy parts that are either part of the problem or were not if you do the job yourself. The real diagnostic equipment is very expensive and only good repair shops have the best stuff. Even then it is still the same thing.

So let me know what you can. Maybe price out an O2 sensor if you have never replaced it as it might need it anyway especially if your going to be towing.

It will work out.

You are definately right to take it to the dealer. Normally, an O2 sensor is part of a full service, the type of service where high mileage maintenance items are replaced, so it would not affect warranty. But you would have to have a 100,000 mile warranty to worry about that.
The fact that a trouble light is not coming on is not unusual. Especially with electrical items, the problem is that they will fail slowly sometimes and until they are bad enough to fall out of specifications that the ECU will trip a code, so it won't throw a light, sometimes even a code reader won't catch it.
Only a dealer will have the type of diagnostic tools to catch that kind of stuff.

Let me know how it all works out.

It is certainly worth doing what they suggested so that they cannot throw it back at you later. I have had the same type of issue where the Tech could not replicate the problem and they blew me off.
It took a long time and I had to go to several dealerships before I got help.

A few things that I found that helped besides getting a second or third opinion are; checking the dealerships records of recalls and service bulletins. Their are Government web sites that keep track of safety related recalls, but do not keep track of much else.
Service bulletins are internal memos that dealerships use to help diagnose problems that are hard to find the source of the problem. It saves them time and money. They will also try not to help with these issues if they think the issue might not get covered when audited by a company rep.
So issues like yours are a high risk for them to fix as the parts are expensive and they might not get money for the job if the company rep. Does not approve the repair upon review.

So, check recalls, service bulletins at some other dealerships and get a feel for the customer service provided. Larger dealerships are more likely to fix this type of issue.

Let me know how it goes as I will keep an eye on this link.

That is great news! I am very happy to hear that you got it fixed without spending any money.
Defincately check around for recals and bulletins that you might not be aware of. They are part of the warranty you paid for and deserve to be fixed if your truck is affected by them. Another thing to remember while youo are doing this is sometimes they will retro-fit vehicles at the plant when a problem is found. They then keep track of the VIN numbers that the fix was put into and the vehicles that did not. So, a dealer might say that your truck is not affected. So, ask for the VIN numbers that the recall/bulletin are for.

I will keep an I on this post link and if you need anything else I am glad to help.
Take care.

There is some truth that the gas is less efficient in winter as Ethanol is added. It actually has more potential energy than gas/petrol, but it depends on the motor. Some do better, some worse.
As far as towing goes, the computer does need some time in, "Hours Driven" to correct itself for best MPG and that happens faster if it is kept in tune.
I don't know if you are using the MPG meter on your dash display or not, but if you are, it is an average of MPG since it was last cleared out. So, it won't react quickly or tell the, "Real-Time" numbers.
Fill up the truck and let the pump turn it off, then write down how many gallons. Do it again and calculate it that way. Unless you already
are.
The dealer is trying to use some truth, but you are right. The cold air is denser and the difference is not going to make it consume 50% more gas. If you went on vacation to the mountains or to an area with a large elevation change from your home, that will make things hard on the trucks' computer as it has to change so many parameters so fast.
Always get gas from a reputable station as the extra cost is worth it. Mobil/Exxon is one of the better ones as they put a detergent in the gas to keep the engine cleaner and they have higher standards for the amount of contaminants in fuel and are very precise with octane ratings. Using the same gas is easier on your Rig as well. The computer does not have to work as much and you can depend on more consistency so the next time your dealer say, "It is that cheap gas you bought one time". You can reply, " No sir, I always use the recommended octane from the same gas station".

Let me know if you need anything else. However, I will be unavailable the next 4 weeks and I will probably loose track of posts that I am working with like this one. You can send me a PM, if it is working, or the team of experts here is a very rare thing. They come from all over the world and we help each other all the time. So, if you can't find me, someone on the team will respond and help you out.

Take Care

Dr. C

Hello,

Ok, here is what I have found on a lot of vehicles.

If you are using the low octane gas you loose milage. First thing I would try is filling up and purchase an Octane Booster and see what happen. In my personal vehicle I have noticed about a 4 - 6 mile gain.

Also have you changed the Air Filter recently. A clogged filter will reduce air flow and create a richer air/fuel mixture.

Another cause and a lot of people don't realize is that Altitude can affect milage. And of course the manufacturers don't tell you that.

.

Hey JD EDWIN,

The original exhaust was damaged so you replaced it?

You will need O2 sensors connected for the engine to run properly, the before catalytic converter O2 sensors are vital to correct engine running.

Are the O2 sensors you disconnected before or after the catalytic converter? If they are before the catalytic converter you will have to reconnect them and ensure they are working first.

The picture attached shows the before catalytic converter (stream 1) and after cat (stream 2).

Do you still have catalytic converters fitted?

Any more information would be great.

Regards, Joe

Hey JD EDWIN,

It will run okay without the catalytic converters but the O2 sensors that were fitted before the catalytic converters must be fitted to the new exhaust for the PCM to get data to adjust fueling.

Without the converters fitted you will have issues with emissions.

Regards, Joe

Ok is the check engine light on? Get back to me

Hello. Thanks for the donation. Much appreciated

Is the CEL (check engine light) showing on the dash display?. This fault could be due to the IAC or MAF sensors or other control sensors? The vehicle should still be under warranty? Have fords check this out for you ! Hope this helps. Let me know