This is on a '99 3.0 Flex coming up on 100k miles. Late last week I got a sudden and very severe decrease in fuel economy. I was getting just shy of 300 miles to a tank. I filled up a couple days ago and have gone 60 miles and am already closing in on the half tank mark. That should tell you its pretty severe. Other than that there is no noticeable difference in the way it sounds/drives/handles. Check engine light is NOT on. I won't be able to tinker with it 'til this weekend, but I figure I'd be on here hitting you guys up for advice anyway so I thought I'd see if you guys had any general ideas about where to start. Someone told me they had a similar problem on an older Ranger that turned out to be a fuel pressure regulator, but I'm not familiar enough with the fuel system to know if the new(ish) Rangers even utilized fuel pressure regulators. The suddeness and severity of it makes me doubt if its the usual culprits, MAF, plugs, plugged cat, O2 sensors, etc... But I don't really know enough to make that call. Any ideas?

 

Let it sit and idle for about 15 minuites then check for any drips underneath , especially under the driver's side.Sounds as if the fuel line has a leak.

 

try some brg engine cleaner you may need to get the gunk out ot the fuel lines and the engine you have better gas mileage after you do this too

 

A fuel gauge is NOT the way to judge fuel usage. For an example you get worried about gas mileage and do all sorts of stuff and buy a bunch of useless crap from the internet to find out you have a defective gauge. :P
When you get to the low point that you normally fill up at, fill and see how many gallons she takes. 1/2 a tank on the gauge isn't going to tell you crap.

Sure you may have a leak but haven't you looked under the truck and walk around it to check for the smell of fuel?

Then again maybe someone stole gas from your tank? It's not so easy as the old days but.....

 

As Victory said, going by how many mile you drive from fill up to fill up is not the way to check fuel mileage. You have to know exactly how many miles you drove since the last fillup and I mean FILL UP. Then divide the miles traveled by the gals it took to refill the tank. Any other way is guessing your fuel mileage.

With that said, maybe someone is borrowing gas from your tank.

 

I believe you, Seth.

I watch my gas guage too and notice if the mpg changes (like it did when I put on new tires). If mine gets less than 90 miles from Full to 3/4, I pay close attention. I'll even top it off and start fresh again. I lost between 20 - 35 miles per tank when I bought tires (same size). I could consistently get 360 miles from a tank, but I do run with the low fuel light on for 3 days (40-50 miles).

The obvious things are: pull your spark plugs out, examine them - they should all look about the same color/wear. You may notice different part numbered plugs installed per side and the electrodes wear differently per side. Ford put single platinum plugs in, different ones for each side. You should replace them with Motorcraft or Autolite double platinums. Chances are, unless YOU replaced them, yours are factory original plugs and DUE for replacement. I'd put new plug wires on too, but that's just me.

That said, check/replace your air filter and confirm integrity of the intake tube and its PCV connection. Probably also due for a PCV valve replacement.

After that, at your mileage (similar to mine, btw) I'd suspect the Upstream O2 sensors may be going bad. They can be bad without setting the CEL.

You could also have a vacuum leak, but since you didn't mention any idle problems, I would discount that idea.

I would also clean your MAF. This is something I had NEVER done before last week. It made a nice difference is smoooooothness at idle and steady speeds. I also ditched the K&N air filter and went back to paper, cleaned the intake tube and throttle body, the IAC, etc. which I'm sure they ALL contributed to the result.




Cliff's Notes: basic tune-up time, worst case = O2 sensors.



Welcome to R-F.



PS. Use the search feature on any of the key word I've used (like IAC, MAF, etc) if you aren't familiar.

 

One reason you can't use the fuel gauge as an indicator is on a cold day the fuel will be denser, tha's less gallons in the tank and a hot day the fuel will expand and there will be more fuel in the tank. When you start the fuel is cool and as you drive and the hot fuel is returned to the tank the fuel will warm up and expand. When you add fuel at the gas station the fuel is cool and then expands with the warm fuel in your tank.

That's not even considering the fact that the fuel gauge is only an relative indication of how many gallons are in the tank and it will vary from day to day.

The bottom line is you don't really know how many gallons are in your tank at a given time because of heat and cold. So if you use the fuel gauge to say you put in 3/4 of a tank of fuel it may never be the same because 3/4 tank in cold weather will be different that 3/4 tank in hot weather.

All your doing is guessing how many mpg your getting.

 

Carl , What you're saying is technically correct.With a 20-30 degree temp change it will happen.

Now after re-reading Seth's first post , He is seeing a change from ~150 miles to 1/2 tank down to 60 miles to 1/2 tank.
You can't tell me the fuel shrunk THAT much! A 90 mile difference on 1/2 tank tells me something is wrong.
Now lets see if we can help him figure out what.

 

Thanks Ken for both posts. I know the gauge isn't a good indicator of fuel mileage. Im not concerned with a small variation in my gas consumption. This was a major swing, it was pretty easy to tell without the math.

Anyway, I do appreciate the input from everyone, but it looks like Ken gets the medal. I sat and let the truck run for a few minutes this morning and checked underneath and there were some drips underneath. You'd think I would've noticed that before but I do leave/get home when its dark most days. So, I'll get it in the garage tonight and crawl underneath it and see what exactlys going on.

 

Some people have had a time with the fittings on the fuel filter , some are rather hard to release and end up breaking or cracking when they go to change it .That's the first place I'd look.


edit:
can i get a cookie instead of a medal?

 

Yes, he has an issue that is not temp oriented. I posted that to make him and others aware of a posible issue of checking fuel mileage.

The fuel in the ground will be around 55-60 deg year round. The above ground ambient temp and temp of fuel in your tank can cause a diff. It's an issue not a given. Just something to watch. That's why gas mileage can vary.

I didn't want to step on Earl43p's post but he made some good points. I'll add don't over look the obvious and check everything.

 

Sure, a cookie sounds like a suitable substitute.

I was finally able to really get underneath it today. I couldn't get it to leak while I was down there, but it was easy to tell the general location of the leak. The front half of the fuel filter and the first half of the short fuel line coming from it as well as everything close to them was covered with gas. I think I'll replace them both for good measure.

 

Ranger Carl- I hate to go off topic in my own thread but thats interesting. So when people say that winter blend gas lowers your mileage, is that what they're seeing or is the winter blend, or what will probably be your answer, a little from column A and a little(lot) from column B?

 

A little of both. It's not a hard fast rule just a guide. They do change the fuel blend summer and winter. There are so many things that affect fuel mileage you can't ever say "I get exactly", it's always "I average".

 

If you are losing fuel that fast, my bet is on a leak. If it was an overly rich mixture, you most certainly have a check engine light, it would be running like crap, and probably smoking like crazy. I'd bet your jettisoning fuel somewhere.

 

do you have a manual transmission? could need a new clutch

 

Just FYI... back in the good ole days of nascar they could about 2 gallons of extra fuel in by pre cooling it to a cold temp. (not sure how cold they got it)

LOL the driver had to very quickly go WOT or else the tank would spew fuel as the gas expanded in the heat.

Rich

 

mine did the same thing, it had something to do with an egr valve or sensor or something im not as technically proficient as some of yall on here but it had to do with the recycling of fuel. well it went out replaced it and all was better. if someone knows the correct term/part im looking for chime in.

 

ROGLMAO, wydopnthrtl, when I first got on this site I couldn't figure you user name and after a day I realized it is WOT. I busted out laughing and I like your name.

Yep, I think they did chill the fuel to stuff more in hoping to burn it off faster than the fuel expanded. I guess it worked most the time.

 

Until the rules caught up with them. The 60s were interesting in Nascar. So many things were tried and to some degree worked *in between* the rules.

Rich (aka WOT aka wydopnthrtl)

 

Yep, my next door neighbor is an old NASCAR driver. He drove mostly in the South West NASCAR program. He raced with or knows almost all the older drivers and has raced with some of their sons. He has told many of his racing experiences. He worked in LA with the movies as a transportation driver and also as a courier service driver. I went with him on a trip to LA and we visited all his old racing buddies and I got to see the shop a friend of his builds the special oil pumps in. Visited another shop that does custom cars for the stars.
We visited Saugus Speedway where he raced when he first whent to LA. Saugus is a flee market now. The track is still there but not used. He started his racing career here in Lou. Ky. around 1956 as a teenager.

My uncle had a speed shop and I would go to the races with him to sell parts in the pits. Got to see some good races and real good fights.