overhead MPG readout..

The information center thing on my 02' Impala read 12 gallons used and about 24 mpg. I filled up today and put 15.25 gallons in and was actually getting 19.4 mpg. Why is my information center so inaccurate? and isn't 19.4 mpg extremely low???

Hmmm....Do you think maybe my catalytic converters are clogged? That would definently cause bad gas mileage, right? Probably the best thing for me to do is take it to a dealer to see if they can recalibrate the overhead info center and while they're at it check out my cats. I know the cats getting clogged is a known problem. Can someone please give me some info on this? Like what's covered under GM or whatever..My car has 73k miles on it. I think I read somewhere that it's covered for up to 80k miles.

The overhead unit needs to be recalibrated.Mine acts the same its off by about 13 pecent.I asked the dealer about recalibrating it 2 yrs ago he didnt no what i was talking about so i just said screw it.

mine is like that too, I think they all are. I just dont think that it can accurately calculate that kind of stuff with how many different factors that are attributed to it. as far as calibrating it. I know you can get the temp calibrated if that is off by more than 3* but I dont know about having the rest of the info being able to be recalibrated. if you go and ask about it or get it done, tell us how much it cost you and if it works.

if it can't be accurate, why put it in? lol. I've seen many other cars that are accurate. Has anyone else tested theirs? How is the accuracy?

What do you guys think about the gas mileage and cat problem idea?

My grand prix and my friends Imp. are dead on

How do you calibrate the out side temp bigrod118??

well I looked in the factory manual that I have, and you HAVE to take it to the dealership, or have there expensive ass little toy that they plug into the diagnostic port.

but it only says it needs to be calibrated if its not within 3 degrees. so thats as accurate as those things are. it may say 70 but it could be 67 or 73 out. that is if it is still within calibration. during the sumer when it got really hot, mine was all over the place. but when the temp is normal (either like 80 or below, mine seems to be right on.) but when it got above 90, ive had it off my 8 or so.

The information center thing on my 02' Impala read 12 gallons used and about 24 mpg. I filled up today and put 15.25 gallons in and was actually getting 19.4 mpg. Why is my information center so inaccurate? and isn't 19.4 mpg extremely low???

1) Change your air filter. 2) Drive Smoother in city traffic. 3) Take a LONGER Average.

Digital Economy readouts on most cars use a function of the MAF (Mass Air Flow Sensor) to estimate the fuel used by measuring the AIR into the intake. Unlike the method of integration used when one simply divides miles driven by gallons filled.

1) Air Flow
When air flow is impeded by blinded filter media the MAF suffers a loss of resolution. Lousy air flow does hurt your actual economy and your estimated economy both. I Like the High Flow cloth filters, any of a half dozen brand names. They’re all better than paper, but don’t OVER clean them. Follow the directions.

2) Drive Smoother
A typical integrating computer algorithm simply adds up many, many, many small blocks of time to get an average for the time period in question. Remember from school, you didn’t turn in your homework and got a zero, it takes three (3) 100’s to get back to a 75 average, ten (10) 100’s to get back to a 90. You get the picture. You floor it getting on the freeway, 0 to 60 in a few of seconds, at 4 mi/gal, it takes 4 times that long to get back to 75% of cruising mpg and 10 times to get back to 90% of cruising mpg. Do that stop light to stop light a few times and the computer average will just not recover. The Digital Display is correct, yet different from what you figure at the end of the tank. Both are correct, within their respective margin of error.

Try coasting down ramps and up to stop lights, try not to floor it more that twice a day, set your cruise at or just below (1-2 mi/hr) the speed limit and leave it there for a week and see what happens.

2) Longer Average.
You can't simply compare one single fill-up to the next. Unless you fill up at the same station and pump every time, you have to allow for differences in the pump. There can be as much as a 2 percent error allowed in the pump in some states. (If you fill up at two pumps at opposite ends you could have a 0.8 gallon error between two 20 gal fill-ups.) Even though you fill up at the same station and same pump every time doesn't mean you get the same gas. All gas in the US (All fuel gas & Diesel) gets pushed through common distribution pipelines to a fuel depot. Many refiners put fuel in one end and a buyer takes the same amount out of the other end. BUT it’s not usually the same fuel. Some "Brands" do “burn cleaner” through the use of Proprietary Additives introduced by the vendor at the fuel depot before distribution. Also, city gas is junk (California and many Large Metros), these “oxygenated” blends have special chemicals in them to reduce specific emissions such as NOX, SO2, SO3. Although, the blends are pretty good at reducing these emissions, the additives also reduce the overall heat rate of the fuel (BTU’s per gallon). The lowered heat rate of the fuel has the effect of reducing economy.
JC TX 11/2/05

They can be exact.It is like a flow-scan on a boat it measures the fuel going through the line and measures the distance traveled.They can be dead on.The prob is most dealerships dont have anyone smart enough to even understand what we are talking about.It is amazing they can even change oil.

Well I took it to a dealership today and explained the situation. They can't get me in untill Monday morning. But that's fine. The assistant service manager I spoke to had no idea about the catalytic converters having any troubles. But his tech knew they did up to 80,000 miles (which I thought was extended untill 100,000) but doesn't matter because I have 73k anyways. They said it's going to cost $85 just to get the computer diagnostic, which I, of course, have to pay if it doesn't read anything about the cats. I really hope this is the problem. He tried to tell me 19mpg was normal, but after talking with him a while he started to get a little more honest and it came out that, obviously, it's not.

Does anyone know how much it'll cost to have the overhead info center recalibrated? He said it may need a new sensor. This is giving me a headache, I just bought the car a few days ago. I wonder if I have an extended warranty. Hmm.

Any tips/info would be appreciated. Thanks, guys.

yeah I got a tip, before you go buying dealership parts, ask around here. I have a ton of links, and I nkow others have more than me, even if they are stock parts you need there are places that sell dealership parts for less than dealership cost, still expensive, but where at the dealership you may pay 325 for a part, it may be like 240 online. but thats just a guess of how much cheaper ive seen things.

here one link that I know off the top.

www.gmpartsdirect.com (http://www.gmpartsdirect.com)

yeah I got a tip, before you go buying dealership parts, ask around here. I have a ton of links, and I nkow others have more than me, even if they are stock parts you need there are places that sell dealership parts for less than dealership cost, still expensive, but where at the dealership you may pay 325 for a part, it may be like 240 online. but thats just a guess of how much cheaper ive seen things.

here one link that I know off the top.

www.gmpartsdirect.com (http://www.gmpartsdirect.com)

I'm not asking for any parts. My brother owns his own shop so I get all my parts at cost. The cats are covered untill 100,000 miles. I'm asking about the overhead readout..It's something just about only the dealership can do..Anyways, my car is there now, I'm just waiting on the phone call.