i have a 91 ex cab dlx pickup with 189k on the chassis and a new motor with roughly 60k on it. oil changed every 2k miles with full synthetic and bg moa additive.
i used to get between 25 to 28 highway and now im averaging 18 to 19
what happened?
i didnt do anything except put tires on that were the same size but with 30% more tread
things i have done to improve the mileage again:
cold start valve
o2 sensor
cleaned k&n filter
cleaned cold air intake piping
new fuel filter
new fuel pump
new spark plugs
new wires
new distributor
several cans of bg 44k
several cans of bg cf5

things that have been done but not in relation to mileage:
new radiator
new alt
new batt
new bumper
new grill
new brakes front and back


i am at a loss... i am not sure what to try next. all the searches i have done recomed that i change the things ive already changed. i am open to all suggestions.

thank you

 

Well the bumper if it is not stock might be pushing a bit more air and be heavier. Your brakes might not be adjusted properly and could be dragging a bit. My best guess though is that it is winter and winter fuel will give you less mileage than summer fuel. Being as it is colder it will run richer as well. Don't even know what motor is in you truck either. If its a 22r did you ever adjust the valve clearances? On my truck in the summer I get 27-31mpg highway and right now I am down to 21-23mpg. Given mine is a diesel and I don't know where you live I live in some mean cold temps in NW Ontario. My dad has a 91 xtra cab with 5 speed and V6 and his mileage has gone down considerably this winter as with other people's vehicles that I know of.

 

sadly the milage went down in early august... i live in wyoming. its the 3.slow 5spd
the bumper is a stock one pulled from salvage

thank you for the winter milage info though that handy knowledge

 

i would check your drums too. i though mine were fine until i re geared and noticed they stuck pretty good and never felt it driving

 

Has your O2 sensor ever been replaced? Hiw many miles? If more than 100,000, replace the sensor......known fuel hog!

 

depending on how old your gear oil is it could be building up some old residue and would work a lot better with new bearing grease and gear oil everywhere

 

You're wasting so much money by changing your oil every 2k miles that it's ridiculous. Why so often? If you're paranoid, send a sample to BlackStone labs for an oil analysis. They'll give you a good idea about how long you should be running it, and any potential problems with the motor's wear characteristics. http://www.blackstone-labs.com/

Seriously, man, you're straight up wasting money. Even dino oil doesn't need to be changed that often! For what it's worth, I run 8k oil change intervals with a filter change at 4k miles.

 

I would check your temp sending unit. If the ecm is getting the wrong readings from it (ex. it thinks the engine is cold) it will supply more fuel. Seems like you have checked everything else.

 

I would guess that it's the winter fuel. I started a post similar to this since every winter my fuel economy drops.

 

...except he said it changed in August. Bit early for winter gas.

How's it driving? Any discernible power loss?

I'm assuming from your mileage that this is a 2wd, right? If (by some strange chance) this is a 4x4, is the 4x4 disengaging correctly?

Could be your cat is getting plugged, that would cause a drop in power and mileage.

Did you make any other changes in August prior to the mileage drop, even seemingly insignificant ones?

 

Could have a slight fuel leak in a line somewhere, that happened to me on my 81

 

01-25-2011 06:47 PM TNRabbit Has your O2 sensor ever been replaced? Hiw many miles? If more than 100,000, replace the sensor......known fuel hog! 01-25-2011 02:08 PM


yes i did change the 02 sensor about a month ago. but it didnt seem to help.



01-25-2011 07:32 PM de'o depending on how old your gear oil is it could be building up some old residue and would work a lot better with new bearing grease and gear oil everywhere


i had all the fluids drained and replaced with full syn about two yrs ago. i mean it could be that. i'll check to see what it looks like. thank you.

 

i really am just paranoid i suppose. i have no valid reason to change it every 2k...
i will definitely send a sample though. excellent recommendation sir. it will give me peace of mind.

 

i was considering doing that, it was my next step if nobody on this knowledgeable had any other suggestions. i just recently had to do that for my girlfriends jetta too

 

no... no discernible loss of power

it is that strange chance that its a 4wd. it disengages, my tires are a tad low on tread so im constantly spinning only the back tires at stops that have a little gravel on them. deff not intentionally. and the mileage decrease is even worse when i do have it 4wd.

the only changes made within a month prior were the radiator, batt, alt, and belts. i did put in white dash gauges, buckets to get rid of the 60-40, and clear bumper corner and tail lights.

 

what did you do to the truck in August when you first started noticing the decrease? 28mpg is pretty amazing for a 4wd pickup, the majority of us are where you're at right now. if you changed those brakes in August, dragging pads could definitely be a possible culprit.

 

the brakes were done in may...

 

AHA - it's the clear corner lights. They are warping the space/time continuum and causing your fuel to vanish into the past.

...seriously though, none of that strikes me as being an obvious culprit, unless belts were overtightened or something...but that's a pretty wild theory.

From what I understand, 18-19 is pretty good from a 4x4 3.0. Granted, you were doing better before, but that still seems decent.

 

i appreciate your help and ideas thank so much everyone. i am sure i'll be back soon with more questions.

 

mabye that old fuel pump was weak or the old filter was clogged letting less fuel through if less fuel got through mabye it caused better fuel milage lol