strange question....

[imdawrlus]

allright here goes.....its about fuel usage vs. rpm....i'll try to do as best i can to explain the question......i always beleved that the slower the engine rpm the less gas the engine used....eg. say you have really high gears and its to the point of bogging the engine down on the highway, for the sake of simplicity lets say your running 1000 rpm and 80 mph...then say your in the same kind of vehicle with different rear end gears and your going 80 at 2000 rpm.....is the first vehicle going to use half as much gas?? does this make sence?? is this true?? if not can someone please explane to me why its not......also, one of the reasons i ask this is because my gas mileage has been really $hitty latelly, i'm down 4 mpg's from 22 mpg....its allready expensive as it is, but 4mpg is a lot to lose....anyone care to take a shot of what u think happened?? it seemed to decrease almost overnight.......

[T Man]

if it happined "overnight" like you suggested, i would guess it is something in the ecm system. Im not gonna come out and say that this is it, but I would suggest an O2 sensor has gone bad. How long has it been since they have been replaced? About your 1st question, i dont think it would get twice the mileage, but yes, it would have some effect on it i believe.

[bvr775]

Have you recently swithed gas stations??? any extra start and stop driving?

a 94 aey... How many miles did you say it had?

gearing affecting milage is relitive to how hard the engine has to work to start and keep the vehicles' momentum. If you had a sudden change in rpms at speed in the same gear as you normally drive check the tranny, if it's a standered check the clutch. Outher wise to problem lies somewere in the emissions or worse the engine itself.

first check for codes and list any errative engine behavour(surging, hissing, rough idle, high rpm vibration. Then check the sensors themselfs (just because it trows a code dosen't mean it's bad) check timming, plugs, all that good stuff. more than likely with a sudden drop in milage like that it's somthing simple like a vacume line.

[imdawrlus]

i've been using the same gas station pretty steady for about a year now....driving style hasent changed.....its 171K on it....it has had a bit of a rough idle at inital startup of the day....i just changed the coolant temp sensor and the iac valve this afternoon so i'll see if that makes a difference tomorow morning.....also next time i get a chance i'm probablly going to pull all the plugs and look at their condition....any other ideas?? the reason i ask the gearing question is becasue i'm going to be putting new tires on it in a few weeks and want to choose the right size...i want to get the biggest size that wont bog it down and will be BEST for mileage at all speeds....right now i have 3.08 gears....thanks......

[OBI WAN]

""allright here goes.....its about fuel usage vs. rpm....i'll try to do as best i can to explain the question......i always beleved that the slower the engine rpm the less gas the engine used....eg. say you have really high gears and its to the point of bogging the engine down on the highway, for the sake of simplicity lets say your running 1000 rpm and 80 mph...then say your in the same kind of vehicle with different rear end gears and your going 80 at 2000 rpm.....is the first vehicle going to use half as much gas?? does this make sence?? is this true?? ""

For that particulat ideal its no quite half nor close, but the scenerio would be true that better mileage is obtained with the first scenerio over the second.






""if not can someone please explane to me why its not......also, one of the reasons i ask this is because my gas mileage has been really $hitty latelly, i'm down 4 mpg's from 22 mpg....its allready expensive as it is, but 4mpg is a lot to lose....anyone care to take a shot of what u think happened?? it seemed to decrease almost overnight.""

This one I'll give you the reason!

For one its winter and the way we drive is different.
Warm up times for those whom cant get into a cold vehicle
Length in power enrichment until in closed loop are much longer.
Slower driving and more stop and go situations

The second part and the #1 reason
Your Federal Government
During the winter those states which see regularly temps under 40 have the winter blend gas. Winter blend gas is like soda pop, it contains oxygen which is done by using some additives in the gas. Knowing warm up times exist and or longer times in the PE state, they did this to lower emissions. The extra oxygen in the fuel promotes lousy mileage and pinging!! I lost 4 MPG's also and do every winter for the last 7 years or so and its due to the fuel!

[bvr775]

most states run oxygas year round now.
the differnce is the winter gas uses tba or some outher alkahol base to absorb water and keep down on the freezing instead useing the regular nahptha or raffinate. It's called RFG (reformulated gasoline). It sux if it's not blended right. Shell and BP are the only ones blending it right because they use my companey for inspection. we don't forge out test results like intertek dose. We send most of it up north because yankees sux. J/K .

[imdawrlus]

i know that mileage is going to drop a little bit during the winter but i didnt think it would drop that much....most likely like you said it has to do with oxygenated and reformulated gas.....so are some stations known for selling $hit winter gas? do they all sell crap gas in the winter? i'm up on the mass/new hampshire border so it gets pretty cold....i usually get gas at irving but if bvr says shell is a little better i'm willing to try it out....what stations have a rep for selling good gas/bad gas??........thanks for putting up with me..haha....

[LEADFOOT]

Besides the gas issue, I would think that with the lower gear the motor would have to work harder to keep the momentum of the vehicle going. With that gear (if it had a 3.42 or somthing like that originaly) and you were doing 80mph and the motor was turning pretty slow then to me it seems like you would use more gas. Its like with a manual, your going 35 and put it in 5th doesn't it take more motor to keep the vehicle moving? My 2 cents

[1993blazerlt]

I have seen a difference in fuel milage compared to rpm. I drove 250 mile on friday at about 80 MPH and got around 16-17 MPG then today i drove the same route again at 70-75 and got 20-21 MPG same brand of gas and about the same temps outside.

[RickyCRX]

That has nothing to do with RPM; that's a function of drag increasing exponentially the faster you go.