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Old 08-24-2003, 01:48 AM   #1
SpeedPlayer 97sl2
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2002 SC2
Question Terrible Mileage, SL2

I have a 97 SL2a with about 59K miles. Over the past 1.5 months, I've noticed my mileage steadily decreasing. I went from 25 mpg, to 23 mpg, to 21 mpg, and now 20 mpg (as calculated from each gas fill up). This is despite the same driving habits, and, in some cases, an actual increase in highway mileage. If this was all short city driving, then I would understand ~20 mpg, especially since I've gotten that before under those circumstances, but all these tanks are after at least 75% highway. It just doesn't make sense. At first I attributed it to switching to Chevron gas since moving down to this region, but I have been running the latest tank back on the previous Shell, which isn't giving me any better results. The simplest things I can think of first are air filter and spark plugs, which I don't mind swapping out just to see if I get any improvement, even though they are in fine condition. I was wondering if you guys had any ideas short of me checking/replacing my temp sensors, fuel filter, etc, in case those replacements don't work...? Other than that, my car runs and looks better than most of the new cars on Saturn's lot.

Much thanks in advance.

Last edited by SpeedPlayer 97sl2; 08-24-2003 at 02:02 AM..

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Old 08-24-2003, 08:38 AM   #2
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Replace the PCM coolant temp sensor, it's almost as easy as changing a spark plug, and could definitely cause the poor milage you're experiencing.

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Old 08-24-2003, 01:35 PM   #3
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Thanks for the help, Saturn-Eh. I did wonder about the ECTS, but I wasn't entirely sure, since I'm not having any overheating problems, nor does my car run, rev, or shift funny in any other way -- just poor gas mileage. I thought a bad ECTS would also cause for some other symptoms, or am I mistaken...? What about a bad intake O2 sensor? Thanks again.

...
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Old 08-24-2003, 02:11 PM   #4
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Ditto what Saturn-eh mentioned. It's the most likely cause, it's a cheap part and it's easy to replace. That's a can't lose (much) trifecta. Also check the connector and wires for corrosion and replace as needed.

Another thing to check is the engine's operating temperature. If the engine never gets to proper operating temperature, gas mileage will suffer. A common cause of this is a failed thermostat. I have a 93SL1 that had pretty miserable fuel economy which was resolved by replacing the thermostat. Mine cost $14 - genuine Saturn part.

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Old 08-24-2003, 06:36 PM   #5
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An O2 sensor can also cause the mileage you are experiencing, but would most likely turn the SES light on. the Coolant temp sensor however usually fails in a subtle way that starts with low fuel economy, followed by other symptoms later - depending on how badly the sensor has failed. As above, it's cheap, is a common failure, and likely the root of your problem.

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Old 08-24-2003, 09:33 PM   #6
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Thanks for all the help folks. Much appreciated. I'll definately look into those suggestions.

...
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Old 08-31-2003, 07:35 PM   #7
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An unsecure fuel injector would also cause the problem, but most likely you'd have a lot of shaking too. My girlfriends SL2 had the #3 fuel injector become unsecure and it got horrible gas mileage and eventually started to shake real bad. Saturn fixed it free of charge. Just a suggestion...

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Old 09-01-2003, 04:36 AM   #8
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Nope, no shaking.

I just changed the CTS yesterday. I'll see how that goes.

I notice I keep on typing "intake" O2 sensor. What the hell is wrong with me???

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Old 09-01-2003, 07:57 AM   #9
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No worries, mate...

If you want to be technically correct, it's an Exhaust Oxygen sensor.

Cheers,

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Old 09-04-2003, 03:55 PM   #10
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I only have 10K on mine and I feel my O2 sensor has been off since day 1 I get rough idle at times and no better than 36 mpg on my new 02'SL1 my 98' SL would get over 40 on the highway quite regularly. Saturn says that the idle is rough and thats just how 02's are they are not 98's.

...
1995 SL1 oil burner school commuter looks nice...1997 SL1 Gold 5-speed with new junk yard wheels and tires just got 40.4 MPG....2002 SL1 sometimes 45 MPG on a spring highway drive

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Old 10-16-2003, 03:50 PM   #11
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I has some really bad gas fuel mileage on my 78,000 miles SW2. Was also burning a lot of oil thinkiong that this was part of teh issue. Anyhow I added some MOA to the crqnkcase at my next oil change and the oil buring went away and gas mileage increased significantly. Give it a try...

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Old 10-19-2003, 11:11 PM   #12
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whats MOA

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Old 10-20-2003, 09:38 AM   #13
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I think he meant MMO, and that's Marvel Mystery Oil. Very cool stuff.....see the How-To board for more on MMO stuff.

...
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Old 10-21-2003, 12:49 AM   #14
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Synthetics helped smooth out my 95 and 02 SLones also change the airfilter it really does help

...
1995 SL1 oil burner school commuter looks nice...1997 SL1 Gold 5-speed with new junk yard wheels and tires just got 40.4 MPG....2002 SL1 sometimes 45 MPG on a spring highway drive

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