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Mileage '98 STS-a question


biomed93

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OK, I know if you can afford to have an STS your not supposed to care about such trivials as mileage-----that having been said---Ummm

I'm pulling only 17 mpg which I think is not great, granted the car has 110,000 on it

but jeez. I bought her used with 105,000 on it. Seems to run good with no codes.

Another thing, anyone have any trouble with their Bose? My right bank of speakers periodically lose their highs and sound muffled and it bums me out.

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17MPG is good, be happy :D im getting, correction, was getting 14. as far as the bose, i replaced every audio emiting device in my car and replaced them with SPL compition speakers amps crossovers tweeters capacitors subs and more, so i only heard my bose for a week. didnt sound bad. i would think that mybe one of your speakers are blown or theres a short in the wires. ;)

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17 MPG may be normal depending on how and where you drive. I average 21-22 in the winter and 23-24 in the summer but I do maostly highway driving and I don't have a heavy foot. If you are doing city driving you will do much less. Also the STS will get somewhat less because of the higher final drive ratio.

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I get 19.5 around town, and 22-23 on long trips, and that’s with 255/50x16 tires, and somewhat of a lead foot. ;)

Let’s see…you’re has 110k miles on it? You might be able to do a little better…The first thing I would check is the air cleaner..make sure it’s nice and clean. After that, how are the tire pressures? Make sure they are up beyond at least 30psi. I’m currently running 32f, 30r.( Higher pressure would get a little better mpg yet, I just won’t sacrifice ride quality for a mpg or so). After these basics, you may want to check your FPR (fuel pressure regulator) . They have a diaphragm, that like many things wears out over time/mileage. Even a slightly leaky FPR will cost you mpg. Look for it on the driver’s side of the engine, upper right corner, near the throttle body. It looks like a small can with a vacuum hose going to it. Remove the hose and see if you can sense any fuel or fumes coming from the hose or the nipple on the can. It should be dry. If you detect any gas there you should look into replacing it, as it will only get worse, cost you mpg’s and hard starts, especially when the engine it is hot. (Haven’t experienced that, have you?)

I replaced the one on my ’93 STS last spring, and I picked up 2mpg and had much better warm starts. I don’t mean to create any worries here, the FPR is a pretty normal wear and tear item. Easy to replace, and not too expensive. Lots of info in the archives here on that subject, just type in “FPR”. Beyond those….?

'93 STS.. opened, dropped, wide...fast.

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The air filter won't affect the milage on a fuel injected engine like it would on a carburated engine.

Ranger...I have no desire to debate this topic, but...A clogged, poorly flowing air filter will decrease the effiencey (MPG here) on any nomally aspirated motor.

'93 STS.. opened, dropped, wide...fast.

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besides the point my 82 gets 10.5MPG.... :o

10.5 MPG from a HT-4100???? I've seen '76 Cadillacs with the 500 engine get better mileage than that.....That's extremely low even for city driving unless you have it floored all the time... That car was rated 16 MPG city and 24 MPG highway.

Have you checked the diagnostic system for trouble codes?

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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The air filter won't affect the milage on a fuel injected engine like it would on a carburated engine.

Ranger...I have no desire to debate this topic, but...A clogged, poorly flowing air filter will decrease the effiencey (MPG here) on any nomally aspirated motor.

Bob,

I got that straight from the master himself. I only wish I could recall what the post was about so I could find it.

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With my 2000 STS, I average 21 mpg year 'round. I find that my 2000 gets better mileage in the 55 MPH range than my 1993 STS; but my 93 got better mileage at highway speeds. The 93 averaged out at 18.5 mpg year around.

I have kind of a heavy foot or why else would I have an STS?

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The air filter won't affect the milage on a fuel injected engine like it would on a carburated engine.

Ranger...I have no desire to debate this topic, but...A clogged, poorly flowing air filter will decrease the effiencey (MPG here) on any nomally aspirated motor.

Bob,

I got that straight from the master himself. I only wish I could recall what the post was about so I could find it.

Well Ranger, I stand corrected. It was buggin' me, and after a little research, you are correct, Sir!

With modern fuel injection's ability to contol 'combustion events' using the MAP signal and mass air flow meter, the fuel economy will really not be affected by even a fairly clogged air filter and the engine running at partial throttle (cruising speed).

Live and learn.. ;)

'93 STS.. opened, dropped, wide...fast.

user posted image

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JMO experience in deference to the above posters. "98 STS"- On breakin around the city 15.5 to 16.5. After 8K mi it went to 18.4-18.9 around the city, 24-26 highway (with WOT out of toll plazas, just cant resist it).

Around 20k city mileage began dropping to about 16.9-17.3 city. Replaced air filter, which was dirty and fuel filter (in case of dirty gas) and mileage went back to original. Has 25.8k on it now.

Doesn't burn any oil in 5K change intervals as I have heard that others do.

If you spend a lot of time in stop and go and bumper to bumper traffic it will affect the computer mileage readout. Your best guage will be a long highway trip. If you get 22-26 0n that all is well.

The last time I drove from Saratoga, NY to Trump Plaza in AC I pulled into entance at 26.4 av. mpg with WOT'S out of toll plazas and av speed of 62.3.

The traffic moves at about 80mph on the Garden State and the troopers don't budge.

Hope this helps.

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my 99 gets 17-19 average, and 24-25 on highway drives. 17-19 average being me with a lead foot but also including some small highway drives. I think the SLS might get better highway mileage due to the small gear ratio difference

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The air filter won't affect the milage on a fuel injected engine like it would on a carburated engine.

Ranger...I have no desire to debate this topic, but...A clogged, poorly flowing air filter will decrease the effiencey (MPG here) on any nomally aspirated motor.

Bob,

I got that straight from the master himself. I only wish I could recall what the post was about so I could find it.

Well Ranger, I stand corrected. It was buggin' me, and after a little research, you are correct, Sir!

With modern fuel injection's ability to contol 'combustion events' using the MAP signal and mass air flow meter, the fuel economy will really not be affected by even a fairly clogged air filter and the engine running at partial throttle (cruising speed).

Live and learn.. ;)

Had to chuckle when I read your post Bob. It was bugging me to but for the life of me I could not find the post to prove it. I had the same "old school" belief as you until I read a post by Guru explaining it. It seems as technology changes, everything we've learned over the years goes right out the window. :(

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That really is some interesting info. Now does that apply just at cruising speed or in general. Because I'm starting to think that perhaps I've been changing out my air filter too often.

-kg

"Burns" rubber

" I've never considered myself to be all that conservative, but it seems the more liberal some people get the more conservative I become. "

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My 97 Eldorado got 30mpg for the three years I had it. Pretty much all two lane highway driving. If I kept it under 60mph, it would get 30+. My 01 STS gets considerably less on the same 240 mile weekly excursion thru the Iowa countryside. Somewhere in the vicinity of 22-25. I did change my fuel though from 93 octane ethanol on the Eldo (since premium was a requirement) to 89 octane ethanol on the STS (no premium requirement -yay!) I think it will even out pricewise- 2.05 for the 93 octane, and 1.75 for the 89.

Really though, gas has come down in price over the past 50 years if you consider the buying power of the dollar and percentage of household income. Remember- pepsi is 6.88 per gallon. If running one mile burns 100 calories and there are roughly 1728 calories in a gallon of pepsi... thats about 17 miles per gallon if 100% efficiency would be assumed. Sometime I'll have to do the conversion using coke and ethanol ;-)

That would make my 240 mile trip cost 97 bucks! Being lazy is cheap. Drive a Caddy.

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>Had to chuckle when I read your post Bob. It was bugging me to but for the life of me I could not find the post to prove it. I had the same "old school" belief as you until I read a post by Guru explaining it. It seems as technology changes, everything we've learned over the years goes right out the window. <

Ranger, when I consulted the 'experts" ;) I was told that theoretically my physics and chemistry are correct, but in practical application here with modern fuel injection it will make a very insignificant difference.

>That really is some interesting info. Now does that apply just at cruising speed or in general. Because I'm starting to think that perhaps I've been changing out my air filter too often.<

Kger, a horribly clogged air filter here will only impede the efficency at WOT.

Having in floored all the time will screw up mpg at any rate 'ey? ;)

'93 STS.. opened, dropped, wide...fast.

user posted image

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BIOMED93,

I wouldn't be too concerned with 17mpg avg. I'm averaging between,

16-18 mpg for city with some hwy driving with my 98 deville 86k miles

on her. However she still gets me about 30 mpg on road trips. I think

what you're getting per gallon is about the norm. Have you stretched

her legs out yet ( long road trip)? You'll be amazed providing you don't

drive 100 mph at the mpg it gets you.

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