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I recently purchased a 98 4.6 HSE with 105,000 miles. I love it and it runs great. There are no problems except I am getting less than 10 MPG. I am driving it as easy as possible and the gas mileage is still terrible. This seems less than it should be getting. There are no engine codes or check engine lights. The previous owner got rid of the airbags and upgraded to 20 inch wheels. Could this be causing my problem? Will changing the O2 sensors help? Thanks for the help.
 

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What do you have the tire pressures set to ?

And are you using a pen and pad to determine your mileage or going by what the vehicle computer is telling you ?
 

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If the O2 sensors are not working the engine will run rich, take out a spark plug from each bank and see if they are black. I had one bank running rich and only got 11mph on a UK galon.
Don't trust the cars computer, pen and paper is the best. :thumb:

Sid.
 

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Mine tells me I am getting 16.9 mpg, so I like the car calculations better than using math.
 

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Something to add to the equation are the "ugraded" wheels. If your tyre diameter is different than stock your speddometer and odometer readings will be off. This may add to faulty MPG calcs.
 

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Um yeah, with the 20 inch wheels, thats about right on the gas mileage. my 2000 had 23 and after putting those on I dropped to below 9 mpg. I had them on for about 3 weeks and took them off. Never again. The board is right though, little maintence here and there, plugs, wires, o2 sensors, etc, you might get a 2-4 mpg extra out of it. I would start by removing the wheels, put on some normal rims and see how much better it gets.
 

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Discussion Starter #7
Thanks for the replies. I am using pen and paper to determine mileage. I will check the plugs and O2 sensors. Why would the larger wheels have that much of an effect? Should I replace all of the O2 sensors?
 

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The wheels will make no difference at all. It is the rolling diameter of the tyre that makes a difference. Ir your diameter is the same as the 255/55 18 tyres that were stofck then you would be fine. If your tyres have a larger diameter then yes it can make quite a difference depending on how much difference there is.

plugs can make a difference, but you would most likely experience rough idle if they were really bad. Cleaning your MAF can make a huge difference. However with MAF and O2 you would receive a CEL if things got too far out of range. Don't forget your air cleaner as well.
 

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Wheels make no difference????????? cough cough


Let me explain something here from someone experienced in the realm of rims. modifying you wheels "could" have a dramatic impact on both performance and gas mileage in both a positive and negative manner. Bigger wheels add additional weight, those wheels above added almost 80 to 100 poounds per wheels on each axle. So adding weight to a car doesnt lower gas mileage :think: I thinks otherwise. I know otherwise. Both range rovers and my mercedes truck I noticed Significant mileage drops when adding Very larger wheels. The amount of accleration needed on takeoff alone from larger wheels is a gas dropper.

However there are times when it pays off.My Mercedes S class and BMW 740il, both had light alloy wheels put on and acutally gained 1 mpg on both of them. Lighter the wheel, better the mileage, heavier the wheel, less the gas mileage.
 

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Assuming there is a weight dif ya got me there. :oops: My mind was stuck on the whole odo being off thus MPG calcs being off and weight hadn't entered my feeble mind. I'll bow my head and go get some coffee now.. :?
 

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2002-2005 Range Rover MkIII / L322
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vmystikilv said:
those wheels above added almost 80 to 100 poounds per wheels on each axle.
Not even close to 80 pounds man. C'mon. Were they made of lead? I doubt they even weigh 80 pounds each, much less added 80 lbs to it.

BUT.... adding weight as rotating mass (wheels, tires, brake rotors) has a multiplied effect on the actual weight savings/addition.
The norm is that every pound is the equivalent to adding approximately 7x that amount to the weight of the vehicle. So...if your wheels are 10 lbs heavier than stock, it's like adding 70 lbs per hub...so 280 lbs total. That makes a big difference in acceleration and stopping.

Every 100 lbs is saves/adds approximately .1 second to 1/4 mile time.
 

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On two of my three 38's the day I got them I scrapped the 16s for the 19" MKIII's. Cars ran fab and gave perfect milage. Almost 300 miles on a tank on 99.9% highway on speeds of 100-110 kph and around 250 ish on normal city highway mix.

And I agree about the weight as well. even if you subsituted them with steel wheels you still would'nt gain up to 100 pounds a side !

P.S : I know personal choice and all but those 20's ..GOD **** ! man they are fugly !
 

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kmagnuss said:
vmystikilv said:
those wheels above added almost 80 to 100 poounds per wheels on each axle.
Not even close to 80 pounds man. C'mon. Were they made of lead? I doubt they even weigh 80 pounds each, much less added 80 lbs to it.

BUT.... adding weight as rotating mass (wheels, tires, brake rotors) has a multiplied effect on the actual weight savings/addition.
The norm is that every pound is the equivalent to adding approximately 7x that amount to the weight of the vehicle. So...if your wheels are 10 lbs heavier than stock, it's like adding 70 lbs per hub...so 280 lbs total. That makes a big difference in acceleration and stopping.

Every 100 lbs is saves/adds approximately .1 second to 1/4 mile time.
Son of a gun. Thanks, man. I never even thought of that before.

What about the effect of where the weight is ?
The farther from the axle it is, the more effort required to turn it.
If a lot of it is in the outer edge of the wheel, then the larger the wheel, the greater the force required.

Does that reasoning hold water or is it full of holes somehow ?
 

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kmagnuss said:
vmystikilv said:
those wheels above added almost 80 to 100 poounds per wheels on each axle.
Not even close to 80 pounds man. C'mon. Were they made of lead? I doubt they even weigh 80 pounds each, much less added 80 lbs to it.

BUT.... adding weight as rotating mass (wheels, tires, brake rotors) has a multiplied effect on the actual weight savings/addition.
The norm is that every pound is the equivalent to adding approximately 7x that amount to the weight of the vehicle. So...if your wheels are 10 lbs heavier than stock, it's like adding 70 lbs per hub...so 280 lbs total. That makes a big difference in acceleration and stopping.

Every 100 lbs is saves/adds approximately .1 second to 1/4 mile time.

Going to massive size wheels will add that much easily. 24's on up. But, like you said, even 10 pounds makes a difference. I never knew the formula for spinning weight, glad to know it now, good call out. And the brakes, yeah, went through front rotors and pads every year with my ML. Very soft pads and going from 16" light alloys to 20 solid disc lorinser killed gas and brake longevity. But, it sure looked good

my 2001 22"



My old ml, I loved this truck :')


my 2000 23"


same 2000 19" and bliss
 

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Discussion Starter #15
Thanks for the input. I tend to think that the wheels wouldn't cause such bad gas mileage by themselves. I am hoping to due a tuneup sometime soon. Hopefully that will help.
 

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Kev,

I will go out on a limb here and say that I am 100% sure it is your O2's. My 97 was pulling 11mpg on open freeway in NorCal. Changed the O2's and it went to 19mpg next day and has stayed that way for the 3 years since I did it. Same drive, same speed twice a day and same distance to work from home. No variables, just new 02 sensors. I changed them myself in 30 minutes on the driveway with no special knowledge - just this wonderful forum!

:clap:
 

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You machine wasn´t weighed down with accessories like a winch etc or towing a heavy trailer was it?
Just out of curiosity what speeds have you been driving at? They do get quite thirsty the faster you go and I have been told by a specialirt RR mechanic to use the cruise control as much as possible. He said that any sort of extended period at the same speed - kick on the cruise control. Even 4-5 miles in a 40mph(70kph) - kick it in. As a matter of curiosity I did some economy tests today on my ´95 4.6 hse and got the following from a 10 mile trip either way. Going to work at 6am, very light traffic at 100kph = 21 mpg. Coming home at 5.30 in medium/heavy traffic (long holiday weekend over here) at 80-85kph = 24mpg.
Ok ours are imperial gallons not US ones so a recalculation would be needed to get an idea and these figures were taken from the trip computer. Can anybody explain why we shouldn´t trust the trip computer? Just my 2c worth.
 

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Personally I think the trip comp is close enough to use. The last time I put on new wires and plugs though, I did get a nice bump in mileage for several thousand miles.
 

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I like those wheels a lot, very nice :clap:
 
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