Taking to shop for MPG issues; what to check?

[jblc]

I suspect there is a vacuum leak and this could be confirmed by looking at the fuel trim. Two possible explanations for the decrease in MPG would be worsening of the leak or perhaps that the spark plugs are fouled.

Definitely interested to hear what you find.

Interesting ideas -- good point on spark plugs as well (nobody's brought that one up yet). That would mean they'd have to have been damaged on arrival, right? If mpg was poor out of the gate.

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[Nomadjohn]

Interesting ideas -- good point on spark plugs as well (nobody's brought that one up yet). That would mean they'd have to have been damaged on arrival, right? If mpg was poor out of the gate.

I suppose that could be the case but not what is thinking. I had in mind that the spark plugs were fine but you've been running rich for some other reason which has caused them to foul which has further decreased your fuel efficiency.

 

[got3fords]

Interesting ideas -- good point on spark plugs as well (nobody's brought that one up yet). That would mean they'd have to have been damaged on arrival, right? If mpg was poor out of the gate.

Or wrong ones?

 

[1pt21gw]

Thanks. I do all of these as standard, which is why the poor mileage is frustrating.
(I mentioned in various posts -- but the thread is long so of course it's not expected that you'd read them all

Here is one to try. Disconnect your battery or replace it if you are 2.5 yrs for a while. The truck will reset a lot of the numbers. Some you may not want to lose like settings in the display. It should give you about 400 miles range, when you drive it will adjust again and again to the lowest common average. A tech on here might know an easier way to "reset" it like it has never been driven before with out losing some of the settings.

I have three Fords I drive right now, and I gave up on the mpg thingy once I figured out how it could be manipulated. Tire Pressure is more fun to watch and small air pressure changes doesn't really affect mileage a lot either, more the ride.

Drive and Enjoy! Otherwise the stress and concerns are really never answered and that gets frustrating.

 

[JasonTremor]

Just a thought, how are your front tires wearing? An out of spec alignment would cause drag and reduce mpg. Doesn't explain the recent sudden change unless you battled with a pot hole or curb recently.

 

[jblc]

Here is one to try. Disconnect your battery or replace it if you are 2.5 yrs for a while.
...
It should give you about 400 miles range, when you drive it will adjust again and again to the lowest common average.
...
I have three Fords I drive right now, and I gave up on the mpg thingy once I figured out how it could be manipulated.

I have a solar panel charging the battery, so it's in perfect health so far
I'm not using the onboard mpg indicator -- I'm hand-calculating mileage. I did calibrate the onboard mpg so that it matches to 0.1 mpg, so I could use it if desired.

Drive and Enjoy! Otherwise the stress and concerns are really never answered and that gets frustrating.

Yeah, agreed, and I do drive and enjoy But ALSO I want to resolve the major problems this vehicle has. 18 mpg highway is a major problem. It both costs money, and limits range...

 

[jblc]

Just a thought, how are your front tires wearing? An out of spec alignment would cause drag and reduce mpg. Doesn't explain the recent sudden change unless you battled with a pot hole or curb recently.

Good thought. I had front alignment checked when I replaced tires about 2k miles ago, and they were (or so they say) spot on. The wear looks normal, from what I can see. To your point, perhaps something recently changed in alignment, but I also randomly checked it after the last time offroading.

 

[got3fords]

I have a solar panel charging the battery, so it's in perfect health so far

The point is, letting all electronics reset by disconnecting the battery for a while. I think it's a great idea. I would even add shorting the disconnected positive cable to ground (or vise versa) to discharge any capacitors that keep volatile memory alive.

 

[jblc]

The point is, letting all electronics reset by disconnecting the battery for a while. I think it's a great idea. I would even add shorting the disconnected positive cable to ground (or vise versa) to discharge any capacitors that keep volatile memory alive.

Ah, I see. There have been several instances of the battery being disconnected for a while, as part of the service work that was being done. These were disconnected for a few hours to days each time.
The shorting wasn't done, but after a few hours caps should be discharged.

 

[Rhino]

me over here with 16-17 mpg ?

 

[jblc]

me over here with 16-17 mpg ?

...how? I mean it's not much lower than mine, but just curious what mods you have.

 

[Rhino]

...how? I mean it's not much lower than mine, but just curious what mods you have.

my truck is leveled and has aftermarket wheels and larger tires the issue is the tires i run are E loads and are heavy... before i had c load 32s and i still would get 19-20mpg but my new tires killed what little mpg i had lol

buuuuut ill take this over the 9 i got in my old tacoma

 

[Rp930]

Right, but...mpg truly didn't change I have spreadsheet records to show that it didn't, as I started tracking mpg right away (hand-calculated).
Same as it didn't change on my '97 when adding the topper.

But yeah, agreed it's significant weight. It just doesn't really seem to impact mpg. And actually, that's perhaps expected: highway driving mpg is dictated by aerodynamic and rolling resistance -- not weight. Weight impacts starting/stopping effort mostly, ie city driving. That's why trains can be so efficient, regardless of huge weight: they have low rolling resistance mainly, and maintain a steady speed.

So at highways speeds, without constant accelerating/decelerating, and with the aerodynamics actually improved a bit with a topper, an extra 300 lb won't make a substantial difference for a vehicle that weighs 2 tons.

Said another way, aerodynamic benefit offset by weight penalty, perhaps, leading to about the same mpg. Again -- just for highway, where it's mostly steady speeds.

The topper doesn’t necessarily improve aerodynamics. Lots of information to debunk that. I get what you are saying but it may not be the case at all. Even steady cruise the weight matters. Anyway if I was the dealer I would want the vehicle returned to stock before even considering your mpg. I’m curious how many tanks of premium you tried? It appears you have worried about mpg from the first tankful. I would also say you are comparing your hand calculated mileage to numbers thrown around on a forum which likely came from the instrument cluster.

Concerning over fueling or vacuum leaks, if the system has to correct by very much the system will flag a fault/CEL. Knowing the fuel trim would be a quick check. Anyway good luck.

 

[jblc]

Even steady cruise the weight matters.

It does, but only from rolling resistance; and in that case, relative weights between topper and vehicle matters -- as that impacts tire deformation at given pressure -- and I think it's minimal change.
What other impacts are there besides rolling resistance, at steady cruise? (not a rhetorical question, curious if you have other factors)

I’m curious how many tanks of premium you tried?

Two full tanks of each grade above 87.

It appears you have worried about mpg from the first tankful.

It wasn't worry at first, just due diligence with a new vehicle. I read on the forums that mpg increases after a few thousand miles, so I wasn't worried yet.

I would also say you are comparing your hand calculated mileage to numbers thrown around on a forum which likely came from the instrument cluster.

True, that could be. I think many people hand-calculate though, and the instrument cluster has an error of about +/- 3 mpg if uncalibrated, so even with -3 mpg taken into account, I'm still low.
It also wouldn't doesn't explain why my numbers have started going down.

Anyway good luck.

Thanks!

 

[Rp930]

The accepted spec is 1-2% less mpg per 100 lbs.

Hope they find something. As others have said fuel trim numbers could tell a lot. How many tanks has it trended down?

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