ideal rpm for best mpg

[bobkyle2]

i thought ive seen this somewhere but cannot find this now.. but does anyone know the ideal rpm for the best mpg...right now at 50mph my rpm is 1490...55mph1650rpm...60mph 1790rpm....65mph 1950rpm thanks alot

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[DMD09]

Not sure what your saying, but i looked in my owners manual, practically it says shift(manual transmission) to keep it under 2000 rpms, that's what i do and doing this and coasting in nuetral on hills, i get 20 mpgs!!!

[glc]

I believe the IMRC starts opening up around 2000, so keep it under that.

Coasting in neutral doesn't help - coasting in gear pretty much shuts off the fuel.

[ManualF150]

Drive like me and you will be seeing 22 mpg consistent.

I shift at <1500 rpms. People hate me...

When you do that you get zig zags behind you...

If you don't know what a zig zag is then here's the definition: One in a vehicle, preferably a car, who follows trucks on their rearend as close as they can, and moves in a rapid left to right fashion, to get around the truck by any means possible, including passing on the right on the shoulder, passing on a double yellow or driving in the opposite lane on a 4 lane highway because they are late for their coffee.

[bobkyle2]

haha must have been drunk or somthing when i posted this i dont even remember posting it...but im sure i meant to ask....i have an automatic wondering what the best miles per gallon i have 373's 4.2 265x70x17 tires...and i run about 60mph to work all week and get 15-16mpg....my 02 4.2 245x70x16 355s gets 22 mpg at 60..)which is a stepside ...and way lighter...but i thought mabey there was like a ideal rpm that these engines get the best fuel milege......any one got any clue what im talking about...ha...if not i will know in a few weeks im going to start driving different speeds each week to see my milege decrease or increase...thanks for the help..

[Raptor05121]

Originally Posted by glc

I believe the IMRC starts opening up around 2000, so keep it under that.

Coasting in neutral doesn't help - coasting in gear pretty much shuts off the fuel.

IMRCs open at 2500.

and how does neutral ~ 850 rpm burn more fuel than coasting in 5th maintaining ~1200 rpm?

[glc]

Because when you are coasting in gear, the fuel is shut off. If it shuts off in neutral, the engine would stall.........

[bobkyle2]

glc are talking about coasting in gear with the ignition still on??...because if your ignition is on and engine running it doesnt matter if you are coasting in gear or coasting in nutral theres still fuel entering in the engine...only way coasting in gear would be better is if you shut the ignition off...

[glc]

Coasting in gear with the ignition on will shut the fuel off or shut it almost completely off after a short delay to allow the throttle to close. This is by design, both for fuel economy and emissions reasons. The very second you touch the gas or the clutch the fuel comes back on.

How do I know this? When I'm running cruise control and going downhill, I can feel slight surging. This is the fuel turning on and off. When the speed goes about 2 mph over set speed, the throttle closes and the fuel shuts off. When the speed drops to set speed, the throttle cracks open. The cruise control does NOT surge like that under any other conditions.

Remember, we are not dealing with a carburetor here, which sucks gas down the throat whenever the engine is running. We are dealing with computerized fuel injectors.

[bobkyle2]

if that was true you couldnt push start it ??? or if you was coasting down the road and you popped it in nutreal without pushing the clutch or throttle it would die....
anyone else gpt an opinion .... haha thats hard to beleive .. but maybenot the first time ive been wrong probably not the last

[glc]

The computer is smarter than that. If it senses the rpm's dropping too low, it adjusts both the fuel delivery and the IAC. Believe me - this fuel shutoff is by design - electronically fuel injected vehicles have been set up like this for years.

You ever start off in 1st gear without touching the gas? These trucks will do it by simply letting the clutch out smoothly. The computer prevents it from stalling unless you dump the clutch too quickly.

[bobkyle2]

hmm..never heard of it... wonder how it knows your coasting from just idling down the road

[Raptor05121]

Originally Posted by glc

You ever start off in 1st gear without touching the gas? These trucks will do it by simply letting the clutch out smoothly. The computer prevents it from stalling unless you dump the clutch too quickly.

I've driven carb'd Chevelles and Trans Ams that can do this. its a matter of releasing just a bit not to drop the RPMs below the set idle until you are going fast enough to take your foot off it entirely

Originally Posted by glc

How do I know this? When I'm running cruise control and going downhill, I can feel slight surging. This is the fuel turning on and off. When the speed goes about 2 mph over set speed, the throttle closes and the fuel shuts off. When the speed drops to set speed, the throttle cracks open. The cruise control does NOT surge like that under any other conditions.

so how do you explain that my ECU is telling me im burning ~3.0 GPH in a steady 65 mpg cruise, ~1.8 GPH when coasting in 5th, and 0.35 GPH when coasting in neutral?

when i get the truck back i can make you a video of a short test drive to show you if you would like to see what im talking about. i watch my MPGs and GPHs like a hawk. 62 mph will yield around 2.90 GPH. idle is 0.35 GPH and if you crack the compressor on it jumps to 0.45 GPH.

[bobkyle2]

yeah im thinkin your right raptor... glc ...drive down the road and let off...drive for a few seconds and then shut the ignition off....i bet you feel a big difference in how your truck slows down.. if it cut the fuel off while coasting in gear it would sorta feel like a "jake brake"