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Old 01-20-2008, 12:01 PM   #1
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MPG issues for a 2000S

Please forgive me if this question has already been hashed over many times before. I did a search and couldn't find anything - maybe I didn't use the search correctly, but what kind of real world MPG figures should I normally expect to get in a 2000 S? I know, I know, quit mashing my foot down all the time and it will improve but still I haven't had better than 19 MPG in a tank yet - this is driving mostly highway miles, probably about an 80 percent highway, 20 percent city combination.

I've heard that some people get better mileage after replacing or cleaning their MAF sensor but that's when they get a CEL that indicates a failed MAF. Is it possible to have a component like the MAF or oxygen sensors cause lower gas mileage without causing the check engine light to come on? I've wondered if it would be worth the risk of possible damage to clean the MAF to see if it improves MPG. Or maybe replace the OS? Is there a diagnostic tool I could plug in to the computer that would show any possible issues that could cause lower MPG?

I don't expect this car to be able to get Honda Civic mpg but it seems like it would be able to get closer to 25 or 26 mpg sometimes. Years ago in my 911T I didn't worry too much about mileage because I didn't drive it that much and fuel was cheaper but this car is my daily driver and a few mpg improvement would make a big difference.

Thanks for sharing any knowledge you have about this.
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Old 01-20-2008, 12:53 PM   #2
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When is the last time you changed the oil,oil filter,air filter & spark plugs? Perhaps you should invest in a bottle of Jectron to run threw the fuel system.

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Old 01-20-2008, 01:02 PM   #3
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I was thinking tune-up too. Unless you're a gorilla, there's almost no risk in cleaning the MAF either.
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Old 01-20-2008, 01:12 PM   #4
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My old 01S got 19 city and 26 hwy. I think that's pretty typical.
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Old 01-20-2008, 01:18 PM   #5
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All those things are definitely planned for the near future. I bought this car recently from a dealer and have no idea when those maintenance items were last performed (car has 96K on it) although it runs really well and the oil doesn't appear dirty, but I know that I need to get it a proper tune-up and oil change soon.

Not trying to sound smart, but seriously how many times has your gas mileage improved by 5-6 mpg after an oil change or sparkplug change - unless it's obviously in dire need of new plugs, air filter, clean oil - in my case the car is otherwise functioning nearly perfectly. Very understandable if the car was missing, cutting out, stalling, smoking, etc. then I could see the tune-up and/or oil change being a possibile cause of lower mpg. No doubt the car would be improved by a tune-up/oil change but I'm not so sure it would account for what appears to me to be lower than normal mpg.

Thanks for the feedback - I needed that reminder and I will be changing plugs, filters, oil very soon as you recommended.
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Old 01-20-2008, 01:21 PM   #6
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How are you basing this 19mpg? I've found that the OBC isn't accurate 90% of the time and it's better if you track your mpg on your own. My OBC tells me I'm pulling 20mpg most of the time but by trackign my mileage-to-gallons of gas I'm pulling in higher than that.
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Old 01-20-2008, 01:35 PM   #7
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Quote:
Originally Posted by dkh
All those things are definitely planned for the near future. I bought this car recently from a dealer and have no idea when those maintenance items were last performed (car has 96K on it) although it runs really well and the oil doesn't appear dirty, but I know that I need to get it a proper tune-up and oil change soon.

Not trying to sound smart, but seriously how many times has your gas mileage improved by 5-6 mpg after an oil change or sparkplug change - unless it's obviously in dire need of new plugs, air filter, clean oil - in my case the car is otherwise functioning nearly perfectly. Very understandable if the car was missing, cutting out, stalling, smoking, etc. then I could see the tune-up and/or oil change being a possibile cause of lower mpg. No doubt the car would be improved by a tune-up/oil change but I'm not so sure it would account for what appears to me to be lower than normal mpg.

Thanks for the feedback - I needed that reminder and I will be changing plugs, filters, oil very soon as you recommended.
How many miles are on your car? It could also be the O2 sensors, as you mentioned, but first things first.
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Old 01-20-2008, 01:35 PM   #8
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Quote:
Originally Posted by blinkwatt
How are you basing this 19mpg? I've found that the OBC isn't accurate 90% of the time and it's better if you track your mpg on your own. My OBC tells me I'm pulling 20mpg most of the time but by trackign my mileage-to-gallons of gas I'm pulling in higher than that.
I wish I had the OBC mpg readout. I'm basing my mpg on amount of fuel at each fill-up and the miles traveled since the last fill-up. This number has been pretty consistent over the last, say, 10 fill-ups or so.

I had the OBC mpg readout on a 93 BMW 325is and it was usually fairly accurate compared to the real world, do-it-yourself calculation at the pump at each fill-up - but it was important to reset the computer mpg calculator at each fill-up to make a valid comparision.
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Old 01-20-2008, 01:40 PM   #9
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I know I'm probably whining about 19mpg too much - after all that's still pretty good. It's just that to my exceedingly frugal wife it doesn't sit too well that I sold a 93 Mitsubishi Montero SUV (and a 73 911T) that was getting about the same mpg on cheaper regular to buy this 2000S. So, I get "see I told you should you should have bought the Honda S2000" - and as far as mpg she's probably right. Good car, just not a Porsche.
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Old 01-20-2008, 01:47 PM   #10
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To answer one of your questions.... yes MAF/O2 sensors can be slow to respond or only read correctly in a narrow range and not trigger a check engine light. Both of these items are easily checked by the dealer or Durametric software for use on a laptop.
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Old 01-20-2008, 01:54 PM   #11
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Quote:

"My old 01S got 19 city and 26 hwy. I think that's pretty typical."

Posted by husker boxster.

I, also, have an 01S, and get pretty much exactly this mileage. If you're getting a combined average of only 19 mpg, something's wrong. (Assuming you're not running the hell out of it continuously...)
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Old 01-20-2008, 01:54 PM   #12
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Quote:
Originally Posted by dkh
I know I'm probably whining about 19mpg too much.
My '01 S has mostly had city driving lately and it gets average of 16.2mpg. Last summer roadtrip was 21-28mpg.
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Old 01-21-2008, 08:42 AM   #13
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Quote:
Originally Posted by husker boxster
My old 01S got 19 city and 26 hwy. I think that's pretty typical.
This is what my 2000 S gets. As others have said, making sure maintenance is up to snuff can make a big diff.

Have replaced an 02 sensor in a honda one time and mileage improved by 10 mpg, so the point about checking the sensors as well as MAF is well taken.

In regards to oil, if you are using M1 0W40 it is probably already sheared to a 30 weight (thin) so oil is probably not going to make much of a diff. in mpg. I switched to redline 5W40 for hopefully improved protection and less shear. The car is noticably quieter and smoother but have not checked mpg. I have also noiced it seems to crank faster when starting which is encouraging. No noticable change in power or oil consumption.
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Old 01-21-2008, 09:56 AM   #14
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Something is amiss if you're getting 19MPG combined. I drive with a pretty heavy foot and average 21MPG in mostly city driving and have gotten 26-28MPG on long freeway slogs.

I'd do the usual fluids / filters / plugs / MAF cleaning and see where that gets you.

O2 sensors have a service life, usually 50-60,000 miles. So it isn't out of the question for them to have gone bad.
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Old 01-21-2008, 11:42 AM   #15
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Your car has 96K miles an no known maintenance history. Time to baseline the car.

1) Fresh oil change
2) Fresh oil filter
3) New Air filter
4) Tire pressures? make sure they are up to snuff
5) Might consider MAF/O2 sensor changes/cleanings/replacements
6) You don't mention driving style. My non-S got good highway mileage.. maybe 25-28 but man, it was really bad on the track or AXs .. How you drive will greatly impact mileage returned.
7) Might try some additives to clean out fuel injectors
8) Gasoline... Many folks experience a drop in fuel mileage in the winter time due to oxygenated fuels. It seems in the NE and Mid-Adlantic, MTBE (an oxyginator) has been replaced with ETHANOL blends.. up to 10-15% ethanol added. ETHANOL doesn't have as much energy as gasoline and therefore hurts your mileage. Many states require posting of ETHANOL blends in gasoline so check the pump next time.
9) Catalytic converters get cogged over time as well... something to consider I guess.

Beyond that? not sure what else to suggest.
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Old 01-21-2008, 04:21 PM   #16
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I agree with Husker, Frodo and others. I get around the same in my 2004 S, 19 city, 25 to 27 hwy.

Im kinda anal about it, so I track it. I find it helpful for noting changes either worse or better than normal.

Here is a screen shot of my data, FWIW:
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Old 01-21-2008, 04:45 PM   #17
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You big a$$ picture didnt load, i think the site is still having attachment issues, you'll have to load it to photobucket and post the img code.
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Old 01-21-2008, 05:14 PM   #18
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Kurt W, Awesome data. Can you please shrink the size of the image in a photo editor and edit your original post with the smaller photo? Thanks.
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