poor fuel mileage need help bad

fordmechanic08 · Dec 13, 2013

i have a 2002 ford ranger edge regular cab short bed with a 3.0L v6 4x4 with 4:10 gears stock tire size nothing after market its all bone stock. i know with that low of a gear ratio im not goona get great fuel mpg but im only getting 14 to 15 avg i do mostly high way driving some in town but not much, i kept getting a system lean code in both banks with low fuel mpg then it started missing and bucking real bad under a load going up hills and things like that i work at a ford dealership so i was able to find a techanical service bullentin for the cam syncronizer so i replaced that and ever since then no light has come back on no more miss or buck or anything it is running great but im still fighting the mpg problem? is this kinda fuel mpg normal for a truck like this and im beating my head against a wall for nothing or do i have something unforseen here going on? any ideas would be helpfull

chrmaka · Dec 13, 2013

I'd check your highflow 02 sensor. It would be a good idea to check to make sure your cad is not clogged. If both are good, i'd go with a seafoam and STP treatment.

RonD · Dec 13, 2013

It is a bit below average but highway speeds and 4:10 don't go together well.
Good acceleration though

Yes, Cam syncro needs to be replaced every 80k or so on the 3.0l.

Is your engine running with temp gauge just below 1/2 way?
Does it warm up within 5 minutes?

Gas engines should run at about 210degF for best MPG, Ford uses a 192-195degF t-stat
Some replace with 180degF and wonder why their mileage went down, lol, thats why.
So if temp doesn't climb above a 1/4 on the gauge then t-stat could be wrong or is not closing all the way when cold.

Other thing to look for is a fuel leak, the post '99 systems run at 65+psi, give the fuel rail a once over with your fingers and smell for a gas smell on them, a small leak lowers MPG but won't smell much as it evaporates too fast.
Fuel filter is another location.
And the filler tube and vent tube as well but you usually smell those leaks.

Neighbor with a siphon hose and gas can can put a kink in the ol' MPG as well, lol

fordmechanic08 · Dec 15, 2013

I will check the o2 when I get to work Monday and see what I find... The temp is running just below Half way on the gauge I haven't been able to find any leaks or anything like... I did change the air filter out for a k&n help it breath a little better I will prob do the fuel filter next thank you for the advice

RonD · Dec 15, 2013

O2 sensors are baseline so really hard to test if they are working correctly, nothing to compare them to, unless you swap them out.
With engine warmed up and scan tool connected, and showing real time O2 voltage
Pull off a vacuum line from the intake, that should set a lean voltage watch for it and write it down.
replace vacuum line and let O2 voltage stabilize
Now pull a spark plug wire on that bank, that should change it to Rich voltage.
Generally O2 sensors get sluggish in changing voltage, so slow to react, as they get older they tend to show lean voltage which makes engine run richer than it should.

Downstream O2 sensors(behind cat converter) usually last twice as long as the upstream sensors, so if you are going to replace them just do the upstream.
The downstream sensor is mainly to test if cat convertor is working, but "may" have some effect on lean/rich.

MAF sensor, with air flow and air temp has the most effect on gross fuel/air mix, O2 sensors are for fine tuning that mix.

JP02XLT · Dec 15, 2013

Another method to test the reaction of an O2 is to use a scanner that will data log & graph, then you can see how many changes occur. I like to set the cruise control on 60 and get 15 to 20 seconds of steady 60 mph speed with the engine warm, a good O2 will change about every 1.5-2 seconds, a slow one will change every 5-6 seconds, I have seen them have even longer cycles and not be dead.

The front O2's control the injectors, the rear just checks for un-burnt gasses after the cat

You almost have to graph the data to see all the cycles.

JP02XLT

stmitch · Dec 16, 2013

Does the truck have an auto transmission, or manual? Is it lifted at all, or running larger than stock tires? What are your highway speeds?

fordmechanic08 · Dec 16, 2013

i work at a ford dealership and have access to a ford IDS scan tool witch graphs every sensor you could ever want to look at lol its kinda nice... but by looing at the graph it will give me a good bas line too look at while doing things to make it change the fuel curve, but every thing on the truck is stock no lift no over size tires nothing with an automotic trans no lift, high way speeds are around 65 70 witch puts me right about 2500 rpm

RonD · Dec 16, 2013

The thing about "working" O2 sensors is if they are wrong how do you know..........??

If their voltage shows "prefect" lean/rich balance, you have nothing to compare it to.
Outside of a sniffer up the exhaust pipe there is no way to determine if "working" O2 sensor is reporting accurate Oxygen levels.

bobbywalter · Dec 16, 2013

3.0 auto.....410 gears are perfect for it. but you should know that.

i have seen these range from 15-23 in 2wd ext cabs. brand new :dunno:

whats a vacuum gauge reading look like on it?

did you ohm the wires and do a careful plug inspection?

stmitch · Dec 17, 2013

I'd think high teens would probably be about as good as you would get considering your trucks statistics. 2500 rpm on the highway isn't terrible, but it's not ideal for seeing good fuel economy either.

On my daily driver (01 2WD 4cyl/manual), I was turning 2400rpm @ 70mph, and getting 30mpg. I slowed my travel speed down to 65, which dropped my rpm's down to 2100, and my fuel economy jumped up to 32mpg.

I know it's not perfectly comparable to your truck since it's got a different engine/trans and is only 2wd, but it does illustrate how much of an effect slowing your travel speed a bit can have on your mpg. The engine turns fewer rpms, and there's less aerodynamic drag, its a win/win.

bocefas · Dec 17, 2013

I have almost an identical set up...2001 3.0 5 speed 4WD 4.10 gears 245/75/16 tires...I am in the 17 MPG range and I drive like an old fart so I would have to say what you see is what you're going to get. You could spend lots of time and money on it and maybe get a small improvement, but I would imagine it would take an awfully long time to financially realize any improvement you are going to get. Remember, at the end of the day no matter what you do you're driving a 2 ton brick down the road, not a Prius.

fordmechanic08 · Dec 24, 2013

ok so i've slowed the high way speed down to 60mph and kept the rpms under 3 grand and it has help lol its up to 18mph now i cant complaine about that i guess ha aparently the poor fuel milage had a direct link to my right foot ha

RonD · Dec 24, 2013

You mean the 55mph speed limit was actually a money saver................"say it ain't so Joe"

cp2295 · Dec 24, 2013

I got a 99 3.0 5spd, 3.73s with 31x10.5r15. Summer I get 19 combined, winter I get 16-17 combined.

I'd replace the fuel filter, just as preventative maintenance anyways. Clean the maf with maf cleaner and a toothbrush (light scrubbing!!) don't wanna hurt that sensitive thing. Iat sensor cleaning could help too, it's on the air cleaner duct right in the middle next to the PCV oil breather hose thing... Also coolant temp sensor could be telling the computer you're running colder than you actually are and thus keeping it in An open loop mixture (basically startup mixture which is real nice And rich). You can the fuel pressure-probably not the issue though, I was told the computer has a sensor which measures pressure so when it gets too low it'll make it so the vehicle can't run. But you had the bucking issue which can be caused by fuel filter clogging.. Although it was fixed by changing the cps sensor.

Do you run 5w20? Or 10w40? I run 10w40 because I have a leak, and the difference in mpg is not noticeable at all. Maybe a 1/4 mpg, but you could try it and have different results than me. O2 sensors of course, rockauto has Bosch o2 sensors for $23, and they seem to work just fine. Have you changed your plugs and wires? Better spark means better mpgs. Have you cleaned your throttle body? Just throwing random ideas out there now.

poor fuel mileage need help bad

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