Inaccurate MPG Adjustment

boosted_st · Sep 15, 2022

Not sure if this has been posted before, or maybe I just wasn't searching for the right terms. But thought I would post it for anyone else that wants to adjust the MPG in the cluster if it's off like mine was. I'll check the accuracy over the next couple tanks after changing mine, but it started out about 1.1-1.2 MPG higher than I was really getting.

Take your manually calculated mpg and divide by the computer calculation. Example 21 mpg manual calc divided by computer calc 22.3 = 0.9417. You can round up to 0.942. Multiply by 1000 and you have 942. Plug that number into the AFE Bias using the Engineering Test Mode.

How to access Engineering Test Mode (this worked for me without starting the engine, or starting the engine):

1. Start with the engine off, close the door, wait 30+ seconds until all dash lights, interior lights, and exterior lights are off. I made sure nothing was on.

2. Press and hold the 'OK' Button on the steering wheel (right side) and don't release it yet.

3. Push the Start Button (no brake pedal) to turn on Accessory Mode, continue to hold 'OK' until Engineering Test Mode is displayed on the right of the cluster.

4. Scroll through the screens until you see the AFE Bias screen, press 'OK' to edit, and scroll to adjust. Hit 'OK' to save the new value. The default value is 1000.

5. Once done hit the "Back" button to exit or shut the vehicle off.

CareerFiremanGuy · Sep 15, 2022

Umm, nope!

boosted_st · Sep 15, 2022

CareerFiremanGuy said:

If you aren't comfortable changing anything no one will force you to do so. All this is doing is adjusting the MPG calculation making it more accurate. There are lots of posts on Mustang, F150, and Edge forums about this and no one has said "IT BROKE MY CAR", only "Hey, the MPG is finally accurate"

. Here is a post (another forum post) stating people have been messing with things in this mode since like 2013 or earlier (I found it on my 2013 Focus ST I had, just never changed anything). Because of everything I found, personally, I was willing to take the chance on changing this 1 value, I noted the default and could always change it back. Again, not forcing anyone to make this change, just providing information that I found and used myself if they want to do the same.

CareerFiremanGuy · Sep 16, 2022

boosted_st said:

If you aren't comfortable changing anything no one will force you to do so. All this is doing is adjusting the MPG calculation making it more accurate. There are lots of posts on Mustang, F150, and Edge forums about this and no one has said "IT BROKE MY CAR", only "Hey, the MPG is finally accurate"

. Here is a post (another forum post) stating people have been messing with things in this mode since like 2013 or earlier (I found it on my 2013 Focus ST I had, just never changed anything). Because of everything I found, personally, I was willing to take the chance on changing this 1 value, I noted the default and could always change it back. Again, not forcing anyone to make this change, just providing information that I found and used myself if they want to do the same.

Just being funny.

boosted_st · Sep 16, 2022

CareerFiremanGuy said:

I totally thought you were being serious.

STdriver · Sep 16, 2022

Is there a manual of all of the ETM settings and the impact on the system?

boosted_st · Sep 16, 2022

STdriver said:

Nothing that I found as I was searching for the MPG stuff.

CareerFiremanGuy · Sep 16, 2022

boosted_st said:

Sorry, I was just kidding! Unless it's about a poll on rear bolt shears, don't take me seriously.

boosted_st · Sep 16, 2022

CareerFiremanGuy said:

lol, all good. I'll try to remember that!

FORZDA3 · Sep 16, 2022

I finally settled on 938 for best accuracy. I ran through quite a few tanks of fuel tweaking it up and down to see the changes. 938 is the number that is less than 2 tenths off actual mpg if you’re consistent on the procedure. To get accurate numbers you need to use the same station/pump and stop at the first auto stop, wait at least 15-30 sec then squeeze the handle for one more auto shut off.

As it turns out, both my 2018 Raptor and 2021 ExpST are best accuracy at 938. Seems Ford is pretty consistent that way…

CareerFiremanGuy · Sep 16, 2022

boosted_st said:

boosted_st · Sep 17, 2022

FORZDA3 said:

That number rings a bell, I think that's what a few of the posts I found ended up on as well. With my last tank I came to 925 so might have to adjust that again.

MikeHTally · Sep 19, 2022

CareerFiremanGuy said:

This works fine. I've made the adjustment on the Mustang, the Limited and now the ST. Surprisingly, the ST has been dead-on the past two tanks. The Mustang is < .5 mpg off.

CareerFiremanGuy · Sep 20, 2022

MikeHTally said:

Thanks for posting ...

So was the ST accurate before or after the adjustments? (because you said "surprisingly")

MikeHTally · Sep 20, 2022

CareerFiremanGuy said:

The ST was way off (IMO), as was the Limited. This was not unexpected, so surprisingly I've been able to get the ST way closer than I expected.

I've always had to compensate for the computer's optimistic guess of the mileage. My Ram with new tires was 4.3% off. The Speed 3 was 1.8% off.

I only learned of the Ford's ability to adjust for the error on a Mustang forum. My Mustang was really bad initially. I stopped adjusting since I know the error. Logic tells me it'll never be 100% accurate.

CareerFiremanGuy · Sep 21, 2022

MikeHTally said:

Okay, thanks for the clarification. I've yet to do an old fashioned paper/pen mpg computation, I'll have to set one up.

FYI: the onboard computer is displaying the same 20.0-20.3 mpg on my current ST that my previous ST had shown.

MikeHTally · Sep 21, 2022

Fuelly.com is your best bet. Make sure you fill it. Don't count on pump cut-off. I use my trip odometer, not the "main" one. I've already determined the odo error - I have to add 2.3% to determine the true miles covered since the last fill-up.

CareerFiremanGuy · Sep 22, 2022

Got 'ya.

When all is said and done we're still getting way better mpg than other performance SUV's like the Durango RT (16 mpg), Durango SRT (13 mpg) and Tahoe RST (14 mpg).

Not sure why I really care that much about our ST's mpg!? haha

MikeHTally · Sep 22, 2022

CareerFiremanGuy said:

I hear ya there! The Limited pulled my loaded trailer and still got 17+ while my Ram got 12.8 (best ever: 16.7) and just ignore it if the trailer's back there. And you're right about what's the difference.

I've gotten so accustomed to making my Fuelly entries, I don't know if I could ever stop. My grandfather was religious about tracking fuel consumption. What many folks don't realize that fuel cost is a small fraction of the total, even these days.

I guess the only useable part is being able to detect major changes in mileage even though the driving style/environment didn't change. A sudden drop is a clue that sumpin' ain't right.

CareerFiremanGuy · Sep 23, 2022

MikeHTally said:

Yup! I mean, we've got a 180 cu in V6 engine that makes 400 hp and gets ~20 mpg combined.

60's muscle cars didn't even make that much hp. The 426 Hemi (when carried over unchanged to 1971) was only rated at 350 NET hp and got 9 mpg.

Speaking of 9 mpg, this guy talking about his Trackhawk's mpg and owners complaing about it is pretty dang funny!

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Inaccurate MPG Adjustment

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