real poor gas millage. what could it be? anyone? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 08-01-2007, 01:14 AM   #1
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Default real poor gas millage. what could it be? anyone?

hi my recently purchased (2 months ago) 1995 se is getting extremly low and poor gas millage.. i'm not good with math but i know for sure that 200 miles average on a 18 gallon tank is not good at all in any way, and this is what i am getting.. (200 miles on a 18 gallon tank) with the tank topped off when i fill it up.. i checked for gas leaks and there is none...
here are thing i replaced already-
spark plugs and wires
tp sensor
iac sensor/valve
pcv valve
air filter
oil and oil filter
knock sensor
water pump
belt tensioner

now the only ( 2 ) things i did not change yet are the (( o2 sensor and gas filter)) which i have but am in process of moving so have no time to put on yet..
but i dont think imo that these 2 things alone would decrease my mpg so poorly?

any suggestions or ideas..

oh and my tires are all at 40 psi all the time as i check them at least once a week with my fluids........
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Old 08-01-2007, 01:50 AM   #2
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First of all, when you fill up, take note of the number of miles you traveled as well as how many gallons you fill up with, then divide to get an accurate MPG estimation.

Now, I cannot say for sure what might be the culprit of your poor MPG, but I can tell you from personal experience that changing your O2 and your fuel filter can do wonders for your fuel efficiency.

At the most basic level, I would start with diagnosing your intake/outflow... Essentially, the better your car can get air in and out, the more efficient it is capable of being. Then of course, you would want to factor in any fuel variables you may have and address any known mechanical issues.

I see that you have definitely done some work on trying to fix many factors judging by your post, and I commend you!



Questions...
1.) Did you use any Bosch spark plugs? If so, get them out and replace them with something better. Bosch is satan in our cars.

2.) Do you have a rough idle at all? Have you checked all your vacuum lines for decomposition or bad connections?

And just as a side note, do you know if anything has been done about the UIM/LIM problems that the Series II have? Here'* a link for you to read up on just in case... http://www.bonnevilleclub.com/forum/...e=article&k=38
I know you don't have many miles on the clock, but I know the UIM/LIM issues have been known to happen quite randomly. Also, do you have Dex-cool in there, and has it been maintained? Just something to think about.

I hope this was some help...
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Old 08-01-2007, 09:19 AM   #3
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The number one contributor to poor fuel mileage is the O2 sensor. If it'* not performing it'* duties properly more fuel is used.

Although before you run out and put in the sensor and still have the same issue... we understand what you said about your math skills and would like to help out. The tank is 18 gallons..and it is not possible that you are putting in the full 18 as you would have stalled out. How many gallons on average are you putting in for the 200 miles?
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Old 08-01-2007, 10:44 AM   #4
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Quote:
Originally Posted by BillBoost37
How many gallons on average are you putting in for the 200 miles?
i put about 16 1/2 gallons then i wait untill my low fuel warning comes on then i check my trip meter and my odomoter.. both say i got about 200 to 220 miles on a tank..
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Old 08-01-2007, 10:54 AM   #5
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[quote="mstrwolfgang"]b]Questions...[/b]
1.) Did you use any Bosch spark plugs? If so, get them out and replace them with something better. Bosch is satan in our cars.

2.) Do you have a rough idle at all? Have you checked all your vacuum lines for decomposition or bad connections?
quote]

no i did not use anything bosch but i do have a brand new bosch o2 sensor that my friend got me from autozone where he works.. its the only brand o2 they had that was for my car.... is it that much of a problem if i put it in....?

and as for the rough idle my car idles about 900 rpm when i first start it up..

and i dont no how to check the vaccum lines...
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Old 08-01-2007, 11:56 AM   #6
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i wouldn't use the bosch O2 either
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Old 08-01-2007, 01:56 PM   #7
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could it be cheap gas from the bootleg gas station by my house thats so convient to go to..... i hear alot of bad about them but its 40 feet from my house...
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Old 08-01-2007, 02:31 PM   #8
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I have that same problem, but I get like 13mpg on hot days and at night when the air is cool I get at least 21 mpg. Have you checked to see if your poor mpg came from driving in hot weather? To check for leaks in your vac lines look for cracked/corroded fittings and/or with the car idling spray some carb cleaner at the fittings of your vac lines and see if there'* a change in idle
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Old 08-01-2007, 05:19 PM   #9
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Quote:
and i dont no how to check the vaccum lines...
There should be a diagram on the radiator cover under the hood that shows you the vacuum lines. You can get more hose at your local parts store. If nothing else, just have them chop off a foot or so of fuel line in the proper interior diameter and use that.

I would definitely trade out the Bosch O2, probably go for an ACDelco. Also, 900RPMs seems good, but is there any stuttering or grumbling while it idles or is it fairly smooth?


Just from personal experience... I was getting about 14-16 MPG, and then I installed a 180 degree thermostat and installed the rice pipe intake and created my own coolbox to allow the engine to breathe a little better, and since then (along with a new ACDelco O2) I've increased my MPG to the 19-25 range.
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Old 08-01-2007, 07:39 PM   #10
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Quote:
Originally Posted by mstrwolfgang
Quote:
and i dont no how to check the vaccum lines...
There should be a diagram on the radiator cover under the hood that shows you the vacuum lines. You can get more hose at your local parts store. If nothing else, just have them chop off a foot or so of fuel line in the proper interior diameter and use that.

I would definitely trade out the Bosch O2, probably go for an ACDelco. Also, 900RPMs seems good, but is there any stuttering or grumbling while it idles or is it fairly smooth?


Just from personal experience... I was getting about 14-16 MPG, and then I installed a 180 degree thermostat and installed the rice pipe intake and created my own coolbox to allow the engine to breathe a little better, and since then (along with a new ACDelco O2) I've increased my MPG to the 19-25 range.
is the bosch o2 really that bad or can i use it for about a month or 2 untill i get money for another.. autozone only had bosch o2 for my car at the time he got it for me..like i said i did not pay for it, my friend got it for me frok his job and put it on his tab cause im broke...

and also when my car idles and 900 rpm'* its really smooth with no shakes or stuttering or any grumbling. its really that smooth... im amazed..
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