My friend and I both have noticed that in 5th gear we get worse gas milage than when we stay in 4th, but don't the 2nd injectors kick in at 3,800 RPM or so?

If running in 5th gear at 2.5k RPM's wastes more gas than being in 4th at the same speed, what is the problem?

 

i think the fumes must be getting to you and your buddy, my tranny had messed up and i had no 5th gear and had to drive to work, i was getting horrible mileage it cost me almost double the gas driving it in 4th gear

 

it could be struggling more in 5th
better easy flowing then choking it out

 

does your shifter look like this

1 3 4
|-|-|
2 5 R

 

Fuel mileage depends on load.

If I am driving at 45 mph in my 7 and in 5th gear, at 2.5k rpm, then I will have to give the engine more peddle.

If at 45mph in 4th gear I am running at 3k rpm and barely depressing the accelerator, I am using slightly less fuel. The fuel injectors will pulse every intake pass but will be spraying a bit less fuel to keep the engine at speed whereas lugging the motor at low rpm will use more fuel to overcome the torque requirment of the higher gear.

Everyone always gets caught up on rpm and fuel mileage but it isn't accurate. Load determines fuel mileage, not rpm.

 

Yeah in all honesty it depends on the type of driving you are doing, if there are a lot of hills or something like that where you drive, your story could make sense.

 

a proper combination of low load(vacume) and low rpm will always have better mileage.

 

I was just "I" as an example. In my case since Dallas is practically total flatness, 5th gear is the best for me.

 

Think about friction losses.
The engine is moving more, creating more friction, losing more potential energy to heat.


More friction, more drag, more lost energy.
fourth is infinitely inferior to fifth.

 

Sorry, I was addressing the OP.

 

Although that may be a tiny tiny factor, that is not the main cause a car uses more gas in 4th. Just think about this in simple terms. The more air an engine draws in the more fuel it needs to add to use that air. When you are rolling at 4k rpms it is bringing in more air then at 2k rpms.

 

pshhh who needs 4th and fifth

2nd gear hits about 70-80
3rd will do that or more if you want to save a lil here or there

 

just buy a vacuum/boost gauge and monitor that. you will see when u need to be in 4th or 5th at any given moment. just keep your load level at around 15" and your rpm in a resonable spot (2300-3000)