I have a 2003 f-150 fx4 ext. cab with a 4.6 V8.

Over the last 2 months I have noticed a huge decrease in fuel mileage. It all started in mid-January. I have remote start so I just assumed it was from the extra run time in the mornings. But then in late January I made a 1000 mile round trip and used 4 tanks of gas. The entire trip was Highway with the cruise set to 65 mph and I averaged 12 mpg.

Around the same time I began to have 'hard starts', it would crank for a while, sputter and run at very low rpm's for about 10-15 seconds, thick dark smoke would come out of the exhaust and it would have that 'bad gas/paint thinner' smell to it.

Its about 1000 miles away from my warrenty running out so I took it in to get checked out....2 ford dealerships both told me 'everything checks out' and 'we could not duplicate your complaints'.

With gas prices the way they are everyone just thinks im whinning about it, but the truth of the matter is that 3 months ago I could drive 350 miles on a tank with out the check fuel light going on...now I'm lucky to hit 290 miles.

3 months ago I would divide the number of miles driven by the amount of fuel I put in and got a number between 16 and 17. Now when I do it I get a number from 12-13.

It has a fresh air filter about 2500 mile on the last oil change and the tire presure is spot on.

Any ideas of what is going on here? Any thing I should have done?

Thanks,
Dan

 

How long since the fuel fillter was changed? They do get blocked over time.
Also, If the exhaust smells stinky, maybe the cat is getting blocked.

 

Have you tried a different brand of gasoline?

You're running regular octane fuel, right?

Did the dealership pull the plugs or did they just use the OBDII tool and take it for a test drive? I'd make them examine the plugs.

If you've got a video camera, videotape what's happening.

When this kind of thing happened to my mom's '94 Grandmarquis, I believe the MAF went bad.

 

When I was having problems with my IAC it was a progressive problem. First it would be a hard start; later on it would start hard and then idle roughly around 400rpms. It would smell and billow black smoke. The IAC was fouled up and when it was replaced my truck ran like a champ. If it starts roughly again open the hood and try reaching back and tapping the IAC with something to see if the little piston inside frees up. Use the search to find out where it is located on the truck. This may not be your problem but it sounds a lot like what happened to me. Good luck.

 

Would winterized gas account for at least part of it? Since he mentioned a remote start, I'm guessing the OP is in a cold climate.

 

my fuel milage is now avg 20mpg city with the increase in outside temp. engines uses less fuel. cuttin back the timing.