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Old 03-30-2013, 10:10 AM   #1
Saturn-Desu!
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Dazed Major mileage drop

I've had my SL2 for about 2 month's now and it will usually get between 525 and 600km's a tank but about 5 days ago its dropped to about 350km a tank!

Any idea's why i'd get such a major loss all of a sudden?

Its running fine and no loss of power~


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Old 03-30-2013, 10:17 AM   #2
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Default Re: Major mileage drop

*Just saw the thread with the '01 SL1

Guess I gotta look into this " ECTS" thing Lol
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Old 03-30-2013, 10:24 AM   #3
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Default Re: Major mileage drop

Yes, change your ECTS if you never have. Also, start measuring your fuel usage properly - miles or kilometers per tank is grossly inaccurate. Document your odometer at each fillup, along with how much fuel it took to click off (don't top off). Once you have the gallons to fill and the miles since the last fill, calculating actual miles/kilometers per gallon is easy.
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Old 03-30-2013, 01:02 PM   #4
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Default Re: Major mileage drop

Once you have reliably calculated your MPG, some common issues for drop in MPG:
- Driving conditions and driving style.
- Stuck-open t-stat (and with that slow/weak cabin heat).
- Bad ECTS (temp gauge will gives inappropriate temp value and often there are driveability issues as well) Check the first couple threads in the how-to library form. You can check it without removing it.
- a lazy O2 sensor (might not set a code)
- Dragging brakes
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Old 03-30-2013, 01:45 PM   #5
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Default Re: Major mileage drop

It also may be a good idea to pull the spark plugs out and inspect them. You may want to do a EGR and throttle body clean also. Richpin has youtube videos for that. A compression test would also tell you if you have a cylinder thats becoming lazy.
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Old 03-30-2013, 03:39 PM   #6
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Default Re: Major mileage drop

Just went for a drive and its a pretty hot day,temp gauge seems to be workin(when cruising at like 80kmh its at the 3/8's mark and in traffic it'll go up to the half way point~also putting the heater on does drop the temp~

it has recently had new spark plugs put in, And Heat is strong been great all winter, it does have a new sensor in the exhaust manifold so that one is good, But it could be one of the ones further down the exhaust?

(Check engine light is still on last time it was read it was saying 02 sensor, that's when the exhaust sensor was replaced)
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Old 03-30-2013, 04:33 PM   #7
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Default Re: Major mileage drop

The back O2 sensor (after the CAT CON) does not effect MPG, it only senses whether or not the CAT CON is operating at specified efficiency.

The O2 sensor in the manifold does effect fuel economy. But a new sensor should be OK, if it was one that is intended and fitted for the Saturn and properly installed. It is not uncommon for a generic or universal sensor install to be botched.
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Old 04-01-2013, 05:17 PM   #8
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Default Re: Major mileage drop

Quote:
Originally Posted by Saturn-Desu! View Post
(Check engine light is still on last time it was read it was saying 02 sensor, that's when the exhaust sensor was replaced)
So it's still on? Get the code read (in P0XXX format) and post it here.
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Old 04-02-2013, 10:07 AM   #9
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Default Re: Major mileage drop

Quote:
Originally Posted by Saturn-Desu! View Post
it does have a new sensor in the exhaust manifold so that one is good,...
(Check engine light is still on last time it was read it was saying 02 sensor
Just because it was replaced, doesn't mean the new one is good - just sayin'

Is the new O2 sensor a direct-fit unit, or a universal O2? Is the O2 wiring crimped or spliced to the new unit? As link mentioned, actual code will help figure this out
Quote:
525 and 600km's a tank but about 5 days ago its dropped to about 350km a tank
A tank is not a valid unit of measurement, since there can be several gallons (excuse me, litres ) in variation between tanks.

But that is a noticeable change. In other cars, a bad O2 can cause 20% or so drop
...
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Old 04-02-2013, 10:15 AM   #10
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Default Re: Major mileage drop

I'm not really sure if its a direct fit or universal sensor(was installed before i got the car) And as for how its attached, Umm I think its spliced

I'm gonna try an get the code read today, Not really sure where to have that done~ So i guess i'll just drive around and hit up some shops
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Old 04-02-2013, 11:52 AM   #11
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Default Re: Major mileage drop

Do you have a local auto parts store that does code reading? Also if you look at the front O2 sensor and follow the single wire, it should go to a connector that is clipped onto the shroud of the fan. If there is a splice along this wire, it is a universal sensor which is known to not perform well.
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Old 04-05-2013, 12:02 AM   #12
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Default Re: Major mileage drop

Got it checked~

Came back with P0440
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Old 04-05-2013, 12:22 AM   #13
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Default Re: Major mileage drop

DTC P0440 Evaporative Emission (EVAP) System

Gas cap loose?
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Old 04-05-2013, 12:27 AM   #14
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Default Re: Major mileage drop

No the gas caps not loose LoL

the book that was with the scanner said it could be the sensor before the cat~ but don't think it was a Saturn specific book.
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Old 04-05-2013, 01:25 AM   #15
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Default Re: Major mileage drop

I'm getting terrible gas mileage also... my last odometer reading was 244 miles from Full to Empty. 1996 SC1 SOHC

I did a seafoam treatment at the start of this last fill up and I'm at 244 now with another 1/8 of a tank to go... so it didn't help too much but my acceleration is responsive

I recently changed out the old ECTS to the new brass one.
Ordered a 195 thermostat to replace the old one. My gauge RARELY reads over the first hash and NEVER reaches the halfway mark even in hot long island traffic. Going to do a coolant flush/refill while I have the thermostat out.

I replaced the bosch universal O2 sensor with a Denso. My SES light is on, going to get the codes tomorrow.

Will replacing the thermostat dramatically increase mileage?

Hope you find a solution to the problem as well. My work and college commute around the island SUCKS and I'm spending at least $40 a week to fill up. I can't afford to drive anywhere but work and class!
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Old 04-05-2013, 08:34 AM   #16
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Default Re: Major mileage drop

Quote:
Will replacing the thermostat dramatically increase mileage?
Maybe is ther best anyone can say without knowing why your MPG is lower than expected.

A bad (open) t-stat results in slow an engine warm up and operation below design temperatures, which usually means running rich. It also means poor, slow cabin heat in cold weather. This can have a significant effect on MPG depending on driving conditions, especially in cold weather.

A bad ECTS/circuit means incorrect coolant temperature information reaching the computer resulting in a variety of driveability issues, depending on in what way the ECTS has gone bad. It may or may not set a code. If the ECTs fails indicating a cold engine it hurts MPG (engine runs rich), difficult warm engine starting, etc. (If the ECTS fails detectably, the radiator fan will run continually and the gauge will read mid scale.)

A lazy (slow acting) up stream O2 sensor will result in reduced MPG but will not set a code until it is really bad. The downstream O2 sensor (after the CAT CON) has no effect on MPG. All it does is tattle on the CAT CON performance. The O2 sensor signal is small (under a volt) and it is a bit fussy about installation. It takes some skill to reliably install a universal replacement - most folks are better off getting a Saturn-specific direct fit model.

There are many other factors that contribute to MPG as well, not the least of which are driving style, fuel energy content, road conditions, trip lengths, and other vehicle maintenance factors.
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