Explain This - 11.6MPG

This is what the computer says. In reality I got 15.5 MPG. Usually it is off about 1.5 MPG but today it was way off. Any ideas, anyone else have such a big error?

Yes 15.5 still sucks but I live in the mountains and towed a trailer for 30 miles. I am not complaining about the poor gas milage but complaining about the computation error.

Notes: My odometer is accurate to 3/10 over about 100 miles verified by GPS. The Speed is so close I can not see an error. I do have speedometer recalibrator due to the tire size change and the speed is picked up by the ABS sensors so the 4.88 gear change had no impact. Even before the tires and gears the computation was off a lot.

 

I've heard that some of the Tacomas that have one of the 6-cylinder engines see a drop in fuel efficiency after the TSB computer program update that's supposed to make the engine/transmission run smoother. Did this happen after an update?

 

It has been wrong from the beginning. I was told there is no dealer adjustment available.

 

You said you have larger tires and re-geared it so I imagine that’s the cause.

On my stock 17 DCSB OR, I’ve found the computer mileage estimation to be spot on when I’ve calculated it at the pump.

 

I would take it to the dealership. They should be able to troubleshoot it. Maybe there's another TSB update for this situation.

 

I'll bet it's the tire size change.

 

Still had this problem before tire change and like I said speed and odometer are accurate.

 

I'm not a mechanic, but somehow gas is being lost or consumed at a high rate. Somebody will know on this forum.

Another quick thought is that if you have added/modded anything that adds weight, this can affect fuel economy.

 

Just saw this:

https://www.tacomaworld.com/threads/terrible-mileage-after-installing-cold-air-intake.519049/

Mass air flow (MAF) jumped out at me when reading the responses. Maybe a sensor went out or something that controls/modulates something or another went out.

 

Quick thought after a smoke break:

Check the air filter. However I'd be surprised if this in and of itself would account for a 5-7+ mpg drop in fuel efficiency...but who knows. Worth a shot.

 

That interesting but not related to the wrong computation of gas mileage.

 

Too much skinny pedal?

 

BTW, generally colder air contains more oxygen and to match that more gas can be consumed and you can generate more HP that way assuming the ECU allows that to happen.