what would cause poor gas milage i am getting 6-8.5mpg empty witha 2000 4x4 cc 3.73 maf cleaned fuel filter new new air cleaner. on highway running 65-70 it only gets 8-9 mpg brakes are not dragging and tranny shifting fine i am going to try and replace the o2 sensors btw the truck has 120000 miles on it tranny fluid just changed any advice posted part of the concern but not to many replys

 

I guess the first question is, how are you measuring "miles". Any chance you have non-standard tires and are using the trip computer to determine mileage?

 

stock tires and measuring on paper the worst that was done was half tank which was 15gallons and 70miles on truck best was 140miles on truck with 15.5 to fill at half do not let get past half because of price to fill when empty. truck is unloaded not towing anything. new plugs as well hubs not locked in and no fou wheeling

 

Maybe it's me, but I'm a little confused. Before you can be sure your odometer is accurate, you have to compare it to a known mile. One mile isn't enough, however.

Do you ever drive on an interstate that has mile markers? Now, there's no guarantee they are accurate unless you see one marked "measured mile", which are pretty rare. What I do is note the miles and tenths at a given milepost and watch it until I pass the tenth milepost (start at mp 6, end at mp 16, for instance). Note the miles and tenths again. Subtract first reading from the second and divide by 10. Whatever that number is equals what your odometer says is a mile. If that number =1, you are right dead on, your odo is correct. If it doesn't come out to 1, or very close to 1, you have an error to factor in. If the number you come up with is less than one, all your mpg calculations will read lower than they really are. If more than one, you'll get a false high reading.

If you really want to get into this, read this next paragraphs, if not, skip the next two.

If the number you got after dividing by ten is, say .92 (this will be our example for now), you can still get your REAL mpg by taking all your miles (or mpg's, but not BOTH) and dividing either the miles or mpg's by .92 (easiest done on a calculator). If you like to multiply instead take your .92 and for one time only, divide the number 1 by .92 and then you'll have a number you can jot down to multiply all your future mpg calculations with. In this example I have given you, all your future calculations will be multiplied by 1.08696, so all your mpg's will grow by 8+%. If your mpg's are 8.8 calculated, the real mpg's are 8.8 x 1.08696 = 9.565.

If the number you got after dividing by ten was over one your odo is reading more miles than you are really travelling. If the number was, say 1.13, the odo is showing 13% more miles than truly travelled. To get that easy "multiplying number", take one and divide by what you got, say 1.13. 1/1.13gives you .885. Multiply all your mpg calculations by .885 and the answer is your true mpg's. If you had 17.5 before, your real mpg's are 15.49. It's easy once you get used to it.

I hear some folks who come up with some far out mpg calculations. I have done this for years and the only truly accurate way is to keep track of your fill-ups all the time. Then you know if and when it is rising or falling.

Most of us probably know this, but for those who don't or forgot:

When calculating miles per gallon (and I've done it with kilometers per liter AND figured how to easily convert it to mpg's as well and converted cost from the old DM's to US $ too!) you have to know where you are starting, so it has to start with a full tank of fuel, there's no other way without expensive metering equipment. You're going to use two meters that come for free, well mostly free anyway. The meter on the pump and the meter in your dash, which you have already tested for accuracy, I hope.

Fill the tank the way you usually do. Try to do this pretty much the same way every time because this is where huge variations can come (the smaller the tank, the bigger the variation when filling inconsistently).

You can jot down the gallons if you want, but for all practical purposes, the gallons now are meaningless. Do record the miles on the odometer!

At the next fill-up, try to fill the same way as before. Do write down the gallons and odometer reading now, well, right after you pay for the gas so you don't forget and drive off! Take today's reading and subtract the miles reading from the previous fill-up. Let's say you drove 153 miles since last fill. Take that and divide it by the gallons AND tenths of a gallon (someone I knew rounded all the gallons before dividing...now why go to all this trouble to get a bogus number?) Say it took 17.5 gallons: 153/17.5 = 8.74 miles per gallon. That is the ONLY way I know of to get a good mpg reading.

Now, if you determined that your odometer was off by 8+% as we did in the first example, take CALCULATED mpg's and multiply by 1.08696 (or 1.09, here you can round it up OK) and you get 9.5 (or 9.5266 if you rounded to 1.09) to give you your REAL miles per gallon reading.

Sounds too complicated but once you do it a few times, you'll be a whiz at it.

Dave aka MuddyAxles

 

On your other post there were ALOT of people giving you Great advice and suggestions. You need to get your truck running correctly before you worry about bad gas mileage. You have or did have several problems with the truck and they will cause bad gas mileage.

 

I don't think the original poster has a problem figuring out accurate MPG. Please note that he has 120K miles on this truck and he is NOW complaining of poor mileage. Hydro 37 is more on track here with "get it running right" and then see what happens. I really haven't been around much so I don't know what poblems have been posted.

 

all the dealers and the mechanic are not able to figure out what is going on at this time no codes are coming up and all the problems will come up at times with power loss then will go away but with no codes or any real flucuations in test reading they are thinking after the reflash that maybe a sensos is reading wrong and the pcm may not be picking it up so for now i am trying to get alittle better gas milage until the big problem is solved if i can't then i will have to live with what i am getting for now

 

All 2v and 3v V10 that are working properly get 11-14 MPG ( average 12.5MPG) at cruise RPM (2100@70MPH) when empty no matter how much or little you preform hard acceleration starts from a standing stop.

Lifted trucks loose MPG most of the time

Larger tires loose MPG most of the time (especially with a 3.73:1 gear set)

Some Fuels and especially some clean air blends loose power and have lower MPG

Some PCM codes were designed to limit power and cost MPG because of the ignition and fuel maps not being optimized for max power

OUT of calibration MAF, IAC and Throttle position can cause excessive fuel use
A faulty O2 sensor can cause a over rich command
Low tire pressure can eat fuel
Out of alignment front or rear axles can eat fuel
PCM always in "closed loop" can eat fuel
One or more faulty injectors can eat fuel
One or more faulty COPs or plug boots can eat fuel
Front wheel excessive toe in or toe out can eat fuel
Internal problems in a 4R100 auto trans can eat fuel
4X4 mode engaged can eat fuel
Improper drive shaft angles can eat fuel

A combination of any or all of these will eat more fuel

THIS list is not complete..I am just tired of throwing out suggestions...good luck

 

I think is this was my truck with all these problems, and the dealers or others couldn't fix it, it would not be in my driveway in the morning.

 

Sorry for the misunderstanding. I thought you sounded iffy on figuring your mpg..

My son is going through the same thing with his '97 F150 4x4. It's pretty bad when a garage tells you: "We don't know what it is, we can't help you anymore. Probably ought to get rid of it." And these are people we feel we can trust, been going there for years.

My entire point by suggesting getting an accurate mpg reading was to ensure it was really as bad as you first thought.

fredvon4 points out all the things that will possibly cause poor fuel mileage. Put another way, I was told a long time ago that the best guage of the overall health of your vehicle is your fuel economy.

Sometimes we look right past the horses when looking for zebras.

I have been baffled by probs before too, but this really isn't rocket science and they best tool you have is the process of elimination, by looking, listening, checking, measuring and testing. Sometimes these things are right there in front of you, literally, but overlooked.

I had a bad fuel pump once. I didn't know where the gas was coming from, but I could smell it bad. I looked and looked and only after revving the engine and holding it there for a bit did I notice the spray coming from the old lever-action suction-style pump relief hole. It was there all the time, I had looked there seconds before, but just didn't see it.

Now with sensors and wires and connectors all over the engine compartment we have to look differently than before. Before we checked vac lines, hoses, tubes, connections and clamps. Now we check connectors, wires, sensors, etc. Have to use different tools, different senses.

It's there, you'll find it if you have time to keep looking.

Good luck.

 

sorry for all the post all over i didn't think i would get the answers for power loss from a post about overhead display problems. last question i hope when ibought the truck i had the cooling system flushed and with all the other problems i never paid to much attention to the heating or temp gauge ( knew it was not overheating besides here in new york it has not been cold till just recently) the gauge doesn't even make it to the bottom of the little water thermometer design on the dash is that normal you get very warm air but not hot and the truck could run for an hour and you could remove the cap off the radiator and have a small amount of pressure but not have to worry about any coming out and burning you ( that is a good thing) i was wondering because of some of the problems that i have stated this could solve some of the problems also the gauge reads the same even when towing no flucation sorry again for all the posts hope you all have a great day the hoses are not extremely hot either

 

Didn't know it was running cold. Sounds like maybe the thermostat is either missing or stuck full open (better than full shut!). At least I didn't see any mention of that particular item being checked.

I'd pull it out (if it is there), put it in a pan of water with a thermometer and heat it on the stove to see if it opens and at what temp....just for fun.

Then I'd get a new one of the right temp and put it in. They aren't that egg-spensive.

If it's running cold the computer is running the engine rich like the choke was stuck on. That would kill the mpg's for sure.

Probably wouldn't hurt to disconnect the battery for a while to reset the computer while changing the thermostat. Then you can test drive it and get a fresh set and maybe the problem will go away. I've read that they can be quite sensitive to improper "full operating" temperature, whatever that is for your engine.

Wouldn't running always cold be almost like a bad MAF sensor?

 

i justb changed the thermastat and now the top hose is hot or warm i should say the bottom hose is still cold may be a normal thing not sure anyways the heat is very good now and the gauge has shown a rise above the temp from before so i will now wait and see what the milage is after the change also if the truck was even running for say an hour and the gauge was up at its temp with the old stat in it the exhaust would still have that cloud of smoke and smell a little rich now after up to temp it seems fine and no smoke keep you posted

 

just refueled and still getting 6-7 mpg it is cold and i have been doing short trips alot as of rite now so this could cause the problem for this fill up most of the trips were less than 4-5 miles this week had to work a ton of over time but i am still not sure if that milage is normal for all the short trips any feed back would be great

 

900rr
Have you been using your defrost? If, I remember correctly the A/C works in conjunction with the heater to clear the fog off of the windows. I would try driving with the heater on heat only or off. See if that gives you any change. Plus, look at the COPs/wires as mentioned earlier in the other posts. Then work your way though the other items of the tune-ups these trucks (V-10) require.
Just my thoughts….
Tom