2004 Explorer with 4.6L sudden loss of FE

[walt460]

Our 2004 Explorer with 4.6L has suddenly lost 2mpg. Mileage dropped from 16.4 to 14.4mpg. No codes come up on OBDII monitor. The truck has 116K miles, had new plugs at 90K, and just had a new fuel pump installed at dealer. New tires and new front suspension parts recently and an alignment was done. anyone had this problem? Any idea what could be wrong?

Thanks,

Walt

 

[2Trux]

The tires could be the culprits. A different size or style or air pressure could cause a MPG drop.

 

[drdoom]

Totally agree with 2Trux, in the winter time the air pressure drops at least 1psi for every 10°F. YMMV

 

[IIGood]

I say it all the time...first check the air pressures. Even the slightest drop in pressure can affect the mileage.

And if you got a larger diameter tire, that will impact it as well.

 

[SyberTiger]

Keep in mind that the sticker in the fuel compartment that states air pressure for the tires is based only on factory tires. I've long since changed out my 16" wheels and moved to 20" wheels that have 275/45R20 tires and max stated pressure of 52 PSI. As a general rule of thumb you want to go up to 10 - 15 % within max pressure for best fuel efficiency. For me that's about 45 PSI which is a lot higher than the factory sticker states for those old 16" Goodyear tires it came with.

 

[drdoom]

Looking good Syber.

 

[imp]

What about the cats? imp

 

[SyberTiger]

What about the cats? imp

Well, all he said was his fuel mileage dropped. I'd check the tires, then make sure the MAF sensor is cleaned, etc. etc. The injectors could be dirty. I'd think he'd get a "rich" CEL code if it was running way to rich but maybe it's running just rich enough to lower the MPG and not enough to throw a code.

I'd be interested if it's idling at 650 to 700 RPM nice and smooth.

 

[walt460]

Thanks all for the comments! The tires are new and a different brand than before, but the same size and the pressures are always kept 10-15% below max. The PCM shows no codes, and our local auto parts manager did go for a ride and monitor the Fuel/Air ratio which was always in the normal range and even across all 8 cylinders. He suggested cleaning the MAFS and we did that. He also did a fuel pressure test and tested for leaking injectors when the engine is off.

Do these engines have a "knock" sensor that could have gone bad forcing the computer to reduce spark advance?

 

[imp]

Do these engines have a "knock" sensor that could have gone bad forcing the computer to reduce spark advance?

walt460
A really good point. The 4.0L does have a knock sensor, but I cannot answer for the 4.6L without looking into the wiring diagrams, but I think they do not. Someone will know, quicker than my looking it up. imp

 

[SyberTiger]

Thanks all for the comments! The tires are new and a different brand than before, but the same size and the pressures are always kept 10-15% below max. The PCM shows no codes, and our local auto parts manager did go for a ride and monitor the Fuel/Air ratio which was always in the normal range and even across all 8 cylinders. He suggested cleaning the MAFS and we did that. He also did a fuel pressure test and tested for leaking injectors when the engine is off.

Do these engines have a "knock" sensor that could have gone bad forcing the computer to reduce spark advance?

My 2002 4.6L has two knock sensors, one for each bank. They are located under the intake manifold. You can't get to them unless the intake manifold is removed.

 

[imp]

My 2002 4.6L has two knock sensors, one for each bank. They are located under the intake manifold. You can't get to them unless the intake manifold is removed.

@SyberTiger
Thanks for correcting me! As I understand the PCM idea is to maximize ignition advance as much as is practicable, and rely on knock sensing to istantly cut it back slightly as knock is beginning. If it's possible for a knock sensor to fail in such a way that PCM retards spark, that certainly would decrease fuel economy, as well as cause higher cylinder temperatures, and increase emissions. No idea if that's possible where the sensor is concerned. Also, not sure whether failed knock sensor nis detectable bny PCM to thus throw a code to that effect. imp

 

[mountaineer2004]

Syber, those wheels really do look super, but doesn't it ride harshly?
I thought more rubber, less wheel was better for the ride.
My mounty has 17" and the ride is far from smooth.
I keep the pressure fairly low too...32 psi.

 

[SyberTiger]

Syber, those wheels really do look super, but doesn't it ride harshly?
I thought more rubber, less wheel was better for the ride.
My mounty has 17" and the ride is far from smooth.
I keep the pressure fairly low too...32 psi.

Everything is a trade-off....Life's about choices. Choose comfort vs fuel mileage vs handling vs appearance. I would venture to say that what I noticed was not so much a change in smoothness as I did road noise but I have the pressure at 46 PSI for fuel mileage purposes. Lowering the tire pressure would probably increase the smoothness and probably lower the noise level. Of course my struts are only about 2 years past overdue. I know the rear struts have leaked all the oil out which is why I hear the occasional squeaks when I hit the bumps in the road. I should probably take care of that before giving an opinion on smoothness.

 

[mountaineer2004]

^ wise words in that first sentence.

 

[TechGuru]

Our 2004 Explorer with 4.6L has suddenly lost 2mpg. Mileage dropped from 16.4 to 14.4mpg. No codes come up on OBDII monitor. The truck has 116K miles, had new plugs at 90K, and just had a new fuel pump installed at dealer. New tires and new front suspension parts recently and an alignment was done. anyone had this problem? Any idea what could be wrong?

Thanks,

Walt

Junk watered down gas most likly.

Stick with Top-Tier gas only.

http://www.toptiergas.com/licensedbrands/

http://newsroom.aaa.com/2016/07/aaa-not-gasoline-created-equal/

I personally have experienced the best MPG with Chevron/Texaco gas and the worst MPG with MurphyUSA (Walmart) gas.