Gas mileage blows right now...help!

[saefjordan]

I have a 2007 ST Limited with the 4.6L 4WD with 85k on the clock. This thing is getting terrible mileage all the sudden and I am drawing a complete blank. This past summer I was getting up to 24 mpg at 60mph, and even the city mileage the worst I usually got if I was hard on it was 13.9 mpg. Now I'm down in the single digits and barely get 15 on the highway so something is definitely up.

I recently replaced the following, (breaking the bank):

1. Passenger side exhaust manifold
2. All spark plugs (none broke, followed TSB instructions)
3. Air Filter - Fram
4. Fuel Filter
5. All new tires, stock spec Nexen SUV HT's
6. Thermostat

The truck is not the greatest in the lower rpms but is not missing like it used to before I did the plugs. I also reset the ECM by disconnecting the battery for 10 minutes. Any ideas what it could be or how I could go about checking this thing?

Only things I can think of are a bad TPS sensor or the maybe a O2 sensor from the manifold job. Debating on getting one of the Android code scanners. Let me know if you have suggestions. Thanks!

 

[GSU4x4]

Im not sure what could be wrong, but I have no idea how you were getting 24mpg before. I've never gotten above 21mpg and that was once, mine usually gets 13 city and 18 highway. You def shouldn't be getting single digits if you're not pulling something, but if you're getting around 13 city then I believe thats about par for our 4.6 4x4's.

 

[saefjordan]

You've got bigger/heavier tires though if I remember right...

No joke on the mileage, even though it was the on-board unit I was getting the numbers from. I almost wanna say it was up to 25.5 or 26 on that day at one point. My old man (tundra owner) nearly $hit himself looking at it.

I have to say I noticed the mileage drop the most after I got the car back from the Ford dealer, who replaced the cracked passenger manifold. You would think this would help backpressure and give better mileage. I also replaced the air filter and ran a bottle of 3M injector cleaner the following day. Could the MAF be dirty?

 

[GSU4x4]

You've got bigger/heavier tires though if I remember right...

yeah, you're right

No joke on the mileage, even though it was the on-board unit I was getting the numbers from. I almost wanna say it was up to 25.5 or 26 on that day at one point. My old man (tundra owner) nearly $hit himself looking at it.

I have to say I noticed the mileage drop the most after I got the car back from the Ford dealer, who replaced the cracked passenger manifold. You would think this would help backpressure and give better mileage. I also replaced the air filter and ran a bottle of 3M injector cleaner the following day. Could the MAF be dirty?

Maybe could it be a bad fuel filter? I'm not too mechanically inclined but I wouldn't think a new manifold would make anything worse, and I have heard of guys having clogged MAF's before.

 

[tmsoko]

These numbers just shock me. I have 13K on the clock now and if I am feather lite on the pedal and drive 60-70 on the high way, I get 16.5MPG. Driving 80, I get ~15-15.5.

18 - 20+ is something i have never seem in this truck. Never.

 

[saefjordan]

Again, these are stock 235/65/18's on the truck. At the time I was running Cooper CS4's.

I just cleaned the MAF, put 40psi in all tires, and checked the O2 sensor which wasn't even touched in the manifold job. We'll see how it performs tomorrow.

Keep in mind, I wouldn't be posting this up here if I wasn't really concerned with how bad the mileage dropped. Maybe I should've been posting about how good it was doing back then....

 

[BARtruth]

I have a stock 2008 ST 2WD with the 4.0. In summer I get about 18.5-19.5 and 20-21 on Interstate driving. In Winter I get 17-17.5 and 19 on Interstate. All this according to the onboard system. I suppose that's pretty good.

 

[littlehauler]

did you check plugs to see if running rich you may have a bad coil (cop)

 

[STrac4me]

It sounds like you have covered the basics.....Don't know where to turn next. Maybe a tuner could help you. I drive a mix of city/hwy and get 19+mpg. I drove to Florida on I-95 @80+mph and got 23+. Post up what you find out.

 

[Ticobird]

For what it's worth, I bought my ST new and have recorded every fill-up gallons, miles and cost. I actually have 264 data points. My all-time lowest reading was 16.5 mpg, my all-time high was 23.6 mpg and my all-time average is currently 19.6 mpg with a slight .4 mpg drop since September 2009. That's my contribution and while it's an XLT 4.0 liter V6 instead of a 4.6 liter V8 Limited, I would not think the V8 could get any better gas mileage. I drive with a light throttle foot, rarely exceed 3,500 rpm, cruise on the highway just under 2,000 rpm at ≈ 68 mph, mostly suburban/rural driving and no traffic jams like city drivers might experience.

Here is what I found with a quick search of the internet:

Ford Explorer Sport Trac Engines
4.0-liter V-6 4.6-liter V-8
Horsepower 210 @ 5,100 r 292 @ 5,750 rpm
Torque (lbs.-ft.) 254 @ 3,700 rpm 300 @ 3,950 rpm
Paired transmission Five-speed automatic Six-speed automatic
EPA-estimated# 15/20 - 21 14 - 15/20 - 21
gas mileage#
(city/highway, mpg)*
Source: Manufacturer#
*Ranges in gas mileage estimates are due to differences between rear- and four-wheel-drive models.

 

[GreenMando]

,,,That's my contribution and while it's an XLT 4.0 liter V6 instead of a 4.6 liter V8 Limited, I would not think the V8 could get any better gas mileage. I drive with a light throttle foot, rarely exceed 3,500 rpm, cruise on the highway just under 2,000 rpm at ≈ 68 mph, mostly suburban/rural driving and no traffic jams like city drivers might experience.

I have my 2008 with 4x4 and the V8. I get 25 to 28 highway daily. My last fill up was 11 gallons for 300 miles. I rarely excede 2000 rpm.

 

[floater180]

my first thought is injectors, about every 3-4 months i will run 2-3 tanks of gas with injector cleaner, to keep this great gas they're charging us and arm and leg to use, that works for my '07 st 4x4 4.6 vs. on highway in the mid 20's and city from 16.5 to 18 mpg.

 

[GreenMando]

One bad vacuum hose can drop mileage 10 mpg.
Do you have any codes coming up?