Sudden drop in gas mileage

[PiratePast40]

My 96' Ford F250 with the 460 isn't going to win any environmental awards for gas mileage but it just got worse all of a sudden. Was getting 10-12 mpg with or without towing anything. Then this weekend, it dropped to 7-8 mpg. The triuck doesn't get used often and can easily sit for a month or more without being used.

The neighbor told me that he had a similar problem and he had the injectors cleaned at a shop and that fixed the problem. I've heard that's a waste of money. I've allways used Chevron gas so I'm pretty sure there is adequate detergent in the fuel.

Anyone have any ideas?

 

[oldjeep]

Re: Sudden drop in gas mileage

Air filter would be the first thing I would check - then pull the plugs and see what they look like.

 

[PiratePast40]

Re: Sudden drop in gas mileage

That's what I was thinking too. Air filter looks good but think I'll dig around and check the intake area as well to see if there is anything plugged up in there. Haven't checked the plugs yet but will do that as well.

 

[rbh]

Re: Sudden drop in gas mileage

Just throwing this out there, your truck is fuel injected right.
Does the system reset if you unhook the battery, so it needs to build a new fuel curve when it gets power again.
Did you unhook the battery or did it go dead and you had to jump start it?

 

[QC]

Re: Sudden drop in gas mileage

You're supposed to unhook the boat trailer when you get home

 

[Fishing Dude too]

Re: Sudden drop in gas mileage

is it getting to op temp. Try a new thermostat cheep enough and easy fix.

 

[robert graham]

Re: Sudden drop in gas mileage

My 96' Ford F250 with the 460 isn't going to win any environmental awards for gas mileage but it just got worse all of a sudden. Was getting 10-12 mpg with or without towing anything. Then this weekend, it dropped to 7-8 mpg. The triuck doesn't get used often and can easily sit for a month or more without being used.

The neighbor told me that he had a similar problem and he had the injectors cleaned at a shop and that fixed the problem. I've heard that's a waste of money. I've allways used Chevron gas so I'm pretty sure there is adequate detergent in the fuel.

Anyone have any ideas?

I'd get a mechanic to put it on the computer to find out which sensor, flow meter, catalytic converter, etc. may have failed...kinda tough to eyeball/troubleshoot these modern vehicles. Auto-Zone, Advanced Auto will put it on their code reader for no charge...might identify problem and save you some $$$$ Good Luck!

 

[PiratePast40]

Re: Sudden drop in gas mileage

You're supposed to unhook the boat trailer when you get home

LOL - actually the mileage doesn't change with or without towing the boat. It normally does go down a little when pulling the 5000 lb camper but picks back up going down the mountain!

 

[PiratePast40]

Re: Sudden drop in gas mileage

I'd get a mechanic to put it on the computer to find out which sensor, flow meter, catalytic converter, etc. may have failed...kinda tough to eyeball/troubleshoot these modern vehicles. Auto-Zone, Advanced Auto will put it on their code reader for no charge...might identify problem and save you some $$$$ Good Luck!

Just checked with AutoZone and the guy says that as long as the check engine light isn't on, it won't show any codes.

 

[foodfisher]

Re: Sudden drop in gas mileage

O2 sensor took me from 14>5 mpg w/lots of black smoke under load.

 

[Scott Danforth]

Re: Sudden drop in gas mileage

not sure if this is your exact problem, however it is very common in fords

use electric contact cleaner and clean the MAS.

http://troubleshootmyvehicle.com/ford_maf_clean/cleaning_ford_maf_1.php

dust and pollen that makes it thru the filter gets baked on the MAS and it doesnt read correctly.

 

[bruceb58]

Re: Sudden drop in gas mileage

Air filter would be the first thing I would check.

A dirty air filter on a fuel injected engine does not affect MPG at all.

 

[PiratePast40]

Re: Sudden drop in gas mileage

It does get up to operating temp and I haven't noticed any black smoke but acceleration isn't what it used to be. Tried to pull a couple of spark plugs but can't get the connectors off the plugs. After 97K miles, guess it's time for new wires, plugs, cap and rotor. Scott, thanks for the link to cleaning the mass airflow sensor. Looks easy to get to the throttle body to inspect and clean that too.

BIL wants to borrow the truck so I put a couple of bottles of Techron in the rear tank. I'll fill it up and let him burn that off to see if it helps but I'm really not looking for any miracles there.

 

[bruceb58]

Re: Sudden drop in gas mileage

Just checked with AutoZone and the guy says that as long as the check engine light isn't on, it won't show any codes.

It will show past codes for awhile.

 

[SDSeville]

Re: Sudden drop in gas mileage

My GMC Sierra went from 15/18 mpg to about 8/10. Changed plugs and wires for the 1st time at 97k miles (I know, I know...) and mileage went right back up.

 

[PiratePast40]

Re: Sudden drop in gas mileage

I was under the impression that platinum plugs were designed specifically to last 100K miles. Not that my truck doesn't need new plugs just saying that I thought they were supposed to last 100K. Am I wrong on this?

 

[SDSeville]

Re: Sudden drop in gas mileage

I was under the impression that platinum plugs were designed specifically to last 100K miles. Not that my truck doesn't need new plugs just saying that I thought they were supposed to last 100K. Am I wrong on this?

I thought the same thing. My mechanic said they advertise that but in reality do not last that long.

On my wife's old Expedition, they went out at about 90k and it was so bad that it would miss badly while under a load, usually going up a hill. We thought the tranny was gone. Changed the plugs and wires and all good. You would think I would have learned from that one and changed the plugs on my GMC.

 

[82rude]

Re: Sudden drop in gas mileage

I was under the impression that platinum plugs were designed specifically to last 100K miles. Not that my truck doesn't need new plugs just saying that I thought they were supposed to last 100K. Am I wrong on this?

changed mine this year at 120k,just for so id feel better .on my previous f250 (1988 5 litre) a sudden drop in milage and performance turned out to be the o2 sensor.

 

[PiratePast40]

Re: Sudden drop in gas mileage

Thought I'd try the simple things forst so figured I'd clean the MAP sensor. Turns out that this engine doesn't have one. But I did notice quite a bit of dirt and oil around the throttle body gasket. Removed that, cleaned it, and replaced the gasket. Plugs are pretty rusty so think I'll wait for the weekend to tackle that chore. I'll squirt break free on them every day and keep my fingers crossed. Ther are some pretty scary stories out there about spark plugs breaking off and the work it takes to get them out.

As far as the O2 sensor, think I'll do the obvious stuff first and then get hooked up to a scanner to see what it shows for codes before I replace too many more parts.

On the positive side, this truck reminds me of the early days when you could actually sit on the fender well to work on an engine!

 

[SDSeville]

Re: Sudden drop in gas mileage

After months of crappy mileage and less power, the check engine light came on with an error code of "multiple misfires". That is what led me to plugs/wires. I am sure dozens of things could cause it, but plugs and wires should prob be changed anyway.