Yes, another poor mileage 4.0

[RangerDanger2]

Hey all, just purchased an '04 Ranger with 4.0L, auto, 3.55 limited slip differential, with 42.5K on the clock. Truck runs great, great power, no hesitation, just a pleasure to drive. Just filled for second time and the mileage is 13.5 mpg with 90% freeway at 70 mph and no load what-so-ever.

I'm under the impression this truck and setup should be doing somewhere around 17 or so in-town and around 23 or so on the hwy.

Thoughts

 

[RonD]

Best thing would be to pull out a spark plug or two or three and see if engine is running richer than it should, i.e. darker brown spark plug tips

As upstream O2 sensors get older they start to tell computer the air/fuel mix is leaner than it is so MPG goes down, upstream O2 are recommended for change at 100k miles, but past engine issues can shorten that life

The downstream O2 sensor can do the same, it detects Cat converter efficiency, Cat converters stay hot by the computer giving them a bit of unburned fuel every now and then, fuel is burn in the Cat keeping it hot and working
So it possible the downstream O2 could be failing, or the Cats are

You can get Bluetooth OBD2 readers cheap, under $40
And with those you can watch live fuel data while you are driving which may point to something


If everything looks OK, you could have a fuel leak, check fuel filter area, you can use a fuel pressure gauge to check if pressure is slowly dropping with key off

 

[RangerDanger2]

Many thanks, I will perform your recommendations and see what the results are.

 

[decipha]

make sure you don't have low tire pressure or a sticking brake / wheel bearing / etc...

 

[RangerDanger2]

I've done that already concerning the tire pressure and brakes. I'll be cleaning the MAF tomorrow and I'm probably ordering 4 new O2 sensors just to be safe.

 

[RonD]

So how did the spark plug tips look?

They would be a darker brown if computer is running engine Richer than it should
If they are a good color, light brown, then O2s are fine, but you can still change them

There are 5 things that cause actual low MPG

1. Engine running richer than it should, check spark plug tips
2. Vehicle load has changed, takes more fuel to get it down the road, dragging brakes, or pulling a trailer, most notice the trailer right off
3. Leaking fuel at a connection, fuel injectors, fuel filter, top of gas tank, fuel filter is the only one that can drip on the ground, others are hidden
4. Higher ethanol % mix, in the winter most places run a higher ethanol content because it acts as anti-freeze for fuel lines, ethanol doesn't have the same energy per gallon so MPG goes down
5. Cold weather, cold air is heavier than warm air(hot air rises), so computer has to add more fuel to get correct mix, and that will incease power in the engine, the "winter pep" most vehicles get, but this can be offset by ethanol and it does bring down MPG a bit

False MPG change can be larger diameter tires, speedo/odo errors
Neighborhood kid with siphon hose

 

[97ranger xlt]

70mph highway may not be the best for mpgs but on the other hand since you are in tampa the cold is not
a factor applicable to you! i know up here in this freakin arctic weather we have my truck gets crap for mpg's, together
with the lousy ethanol laced fuel making it even worse. if i get 15 mpg highway at granny speeds and
with a tailwind i'm lucky...

 

[RangerDanger2]

So how did the spark plug tips look?

They would be a darker brown if computer is running engine Richer than it should
If they are a good color, light brown, then O2s are fine, but you can still change them

There are 5 things that cause actual low MPG

1. Engine running richer than it should, check spark plug tips
2. Vehicle load has changed, takes more fuel to get it down the road, dragging brakes, or pulling a trailer, most notice the trailer right off
3. Leaking fuel at a connection, fuel injectors, fuel filter, top of gas tank, fuel filter is the only one that can drip on the ground, others are hidden
4. Higher ethanol % mix, in the winter most places run a higher ethanol content because it acts as anti-freeze for fuel lines, ethanol doesn't have the same energy per gallon so MPG goes down
5. Cold weather, cold air is heavier than warm air(hot air rises), so computer has to add more fuel to get correct mix, and that will incease power in the engine, the "winter pep" most vehicles get, but this can be offset by ethanol and it does bring down MPG a bit

False MPG change can be larger diameter tires, speedo/odo errors
Neighborhood kid with siphon hose

I haven't been able to check the spark plugs yet because my spark plug socket is to small and I ran out of time to check other sockets. I have cleaned the MAF with MAF cleaner and WOW, what a difference that made on power, acceleration, and nicer idle. Tomorrow I'll try more sockets to determine what size the plug is and report back on my findings.

 

[sgtsandman]

In my experience, you will almost never see 23 mpg highway. Granted I live in Southwestern PA where little is flat. At 70 mph, I've seen about 19 mpg on a trip. The best mpg I've seen was on trips where I stayed closer to 60 mph and have come close to the manufacturer's estimated mpg but never it it. Average, every day driving that is mostly highway at 65 mph, I average about 18-19 mpg.

With the mpg you are reporting to get. Some things definitely need some attention but don't expect 23 mpg highway.

 

[RangerDanger2]

In my experience, you will almost never see 23 mpg highway. Granted I live in Southwestern PA where little is flat. At 70 mph, I've seen about 19 mpg on a trip. The best mpg I've seen was on trips where I stayed closer to 60 mph and have come close to the manufacturer's estimated mpg but never it it. Average, every day driving that is mostly highway at 65 mph, I average about 18-19 mpg.

With the mpg you are reporting to get. Some things definitely need some attention but don't expect 23 mpg highway.

Yea, I just found that out concerning the mileage. I was looking at the wrong chart. Hopefully I'll get in the 18 to 20 hwy and 16 - 17 in town.

 

[RangerDanger2]

So how did the spark plug tips look?

They would be a darker brown if computer is running engine Richer than it should
If they are a good color, light brown, then O2s are fine, but you can still change them

There are 5 things that cause actual low MPG

1. Engine running richer than it should, check spark plug tips
2. Vehicle load has changed, takes more fuel to get it down the road, dragging brakes, or pulling a trailer, most notice the trailer right off
3. Leaking fuel at a connection, fuel injectors, fuel filter, top of gas tank, fuel filter is the only one that can drip on the ground, others are hidden
4. Higher ethanol % mix, in the winter most places run a higher ethanol content because it acts as anti-freeze for fuel lines, ethanol doesn't have the same energy per gallon so MPG goes down
5. Cold weather, cold air is heavier than warm air(hot air rises), so computer has to add more fuel to get correct mix, and that will incease power in the engine, the "winter pep" most vehicles get, but this can be offset by ethanol and it does bring down MPG a bit

False MPG change can be larger diameter tires, speedo/odo errors
Neighborhood kid with siphon hose

Pulled out spark plugs and the tips are a little bit dark, dry, but not bad. I've seen a huge performance difference after cleaning the MAF, so I'm wondering if the MAF could have been causing the MPH issue. I have a fresh tank in now and will check once the tank is gone.

 

[RonD]

Yes, dirty MAF changes MPG
Reason #5
As you said performance has changed, lower power/performance means you have to press down a bit more on gas pedal to stay at 40MPH or 60MPH

MAF reads the WEIGHT of the incoming air
Air fuel ratio for gasoline is a WEIGHT ratio, 14.7 POUNDS of air to 1 POUND of gasoline, or 14.7 grams of air to 1 gram of gasoline
Thats what the computer calculates on the fly
In your case it is programmed for a 4 LITER engine, so it knows exactly how many LITERS of air the engine is pulling in at all RPMs and throttle positions, its just math
What it doesn't know is how much a LITER of air WEIGHS at that exact moment
Air at sea level is heavier than air at say 3,000ft elevation
Cold air is heavier than warm air, i.e. "hot air rises" why? because its LIGHTER than colder air

Barometric pressure, thats the WEIGHT of the local air at your location, and it changes, just like the weather does, i.e. High pressure is moving in to our area, sunny sky, or Low pressure is moving in so storm coming

So if MAF is off then computer calculations are off
MAF also only samples 10% of the incoming air, so any small error at the MAF is compounded at the computer TIMES 10

 

[RangerDanger2]

So I just filled up the tank and the 4.0 is now getting 14.4 mpg city driving which is up from 13 mpg highway. All I've done is clean the MAF so far. I did check the plugs and they looked ok. So I'm hoping the dirty MAF was my problem relative to bad fuel economy.

 

[Mike Tonon]

How about o2 sensors? I hear there’s 4 and they’re expensive, but replacing them can improve fuel mileage.

 

[RangerDanger2]

How about o2 sensors? I hear there’s 4 and they’re expensive, but replacing them can improve fuel mileage.

They are a little spendy, and I have considered replacing them. I'm waiting to run a few tanks of gas through it with Sea Foam and the cleaned MAF to see how the mileage does. Right now, it keeps going up so it might have been the dirty MAF and injectors. I'll post my results as the data comes in.