I have 1991 Toyota 4wd 4cyl stock gears that use to get anywhere from 17.5-19 mpg around town... Suddenly ive started only getting 15-16mpg i have changed plugs,plug wires,rotor cap and button,fuel filter,coil and have set the tps ..The truck runs great but the fuel mileage is awful .Any help would be GREATLY appreciated

 

Check engine light on? Status of O2 sensor?

BTW, welcome to YT!

 

Sorry... Replaced the 02 sensor last year and there is no codes ! That's why i'm so baffled ?

 

Have you checked the timing?

 

I'm not a very good mechanic but wouldn't it run rough if the timing was off ?

 

Not always. If you timing was advanced or retarded a little it would still seemingly run ok. Advanced you would feel a little more power and retarded you would feel less.
Now if your distributor was off a gear of timing chain was off a tooth it would run horrible if at all. Check it for codes, check your timing, give it a full tuneup and change your fuel filter if you haven't already. Also if you have to replace your o2 sensor for any reason buy a denso one do not i repeat do not put a Bosch o2 sensor in it. 8 out of 10 people have problems with Bosch o2 sensors in these trucks. Good luck hope this helps.

 

I've done all of the above !!! I'm still doing awful on fuel mileage

 

Tire pressure?

 

Did you change the fuel filter??

 

Why did you replace the O2 sensor in the first place? Was it to see if that was the problem with the poor gas mileage? Maybe put the old O2 sensor back to see. Maybe check the injectors, could be clogged. Sorry, just brainstorming.

 

You don`t say where you live??

Driving habits changed ??More traffic lights

Cranked the AC up if you have it??

Do you buy your fuel at the same place??

Changed tires??

Has the truck gained weight it is interesting how much stuff I pick up over a few weeks.

Just how are you computing your mileage figures ??

Myself I think your doing good for around town I was closer to the 12 to 14 mpg with the hubs locked.