15 MPG to 8 MPG Head Scratcher

[89FourRunner]

Hey all,

hope you are all having a strong start to 2018.

I went on a long holiday trip and noticed I got the worst gas mileage of all time. The truck runs as strong as ever, and exactly the same when I was getting 15mpg....except now I am getting around 8mpg. This thing is chugging fuel.

The exhaust has sprung a few leaks as it is time to replace it, but that is the only real change in the past few months. Can that cause the huge fuel mileage change?

It has had less power than ever these days, and it engine brakes quite strongly, but the bearing are good and so are the brakes...no sticking. Seems like engine braking has become stronger.

What gives? Anyone experience and solve a huge mileage drop like this?

 

[wallytoo]

are you positive you don't have a fuel leak somewhere? anywhere? that's what i'd look for. might be hard to locate unless it is running, or shortly after shutting it off, as the fuel evaporates quickly.

i assume you've noted whether the exhaust is "normal" instead of "black"?

 

[89FourRunner]

Exhaust seems normal color/amount. I have not been able to find a leak visually. That is an idea though I will have to check the lines...they are flaky from rust.

 

[wallytoo]

Exhaust seems normal color/amount. I have not been able to find a leak visually. That is an idea though I will have to check the lines...they are flaky from rust.

i recently swapped out my fuel pressure gauge, which is attached at the CSI union bolt/fitting. i forgot to add teflon tape to the threads, and for the next two tanks of fuel, my apparent mileage dropped from about 20 mpg to 14 mpg. eventually, i wiped my finger at the fitting while it was running, and it came away with damp fuel.


when parked, it evaporated enough not to leave an odor or obvious residue, so it took me a bit to find it; of course, i knew i'd just swapped it in, so it was the first place i checked once i noticed the mileage drop.

tank average is now back up to 18 to 19 (winter blend fuel).

 

[levonhelm]

I've had a similar problem with my 1991 3VZE, used to be ok but now gets horrible gas mileage.

At first I thought the fan clutch was the reason because it had seized and was spinning at full RPM's. after replacing it, no real change.

I've also changed the exhaust (after the cat) and changed front brakes and calipers which allowed me to check on the bearings and everything seemed good to go.

recently did the rotor cap, cables and spark plugs, changed the air filter ect...

After taking it in the mechanic noticed my truck was idling at 1200-1300 rpm even after being warm. so i'm heading down the worm hole now trying to find a cost effective solution to this problem. from what I've read it could be temperature sensor issue, vacuum issue, vane sensor, throttle position sensor, fuel pressure and fuel filter..