Poor Gas Mileage....

Sup guys,

I’m consuming entirely too much gas. I currently live and do most of my driving in the city. Currently I’m consuming about 200 miles per tank which is roughly about 13 miles per gallon. Since initially having this problem I have given my car a complete tune up. I’ve changed the oil (Mobil1 10w-40) oil filter (Mobil1) fuel filter, air filter (K&N) pcv valve, spark plugs, wires and replaced the O2 sensor (denso oem) and I’m still having the same problem. I have a 99 GS automatic w/ a 2.4 engine, 18” rims with the correct tire pressure. I’m stumped! Any one has this problem or has any suggestions on what to look for to resolve it? It would be greatly appreciated.

Also, someone asked me whether I gapped the spark plugs correctly. I informed that that I had not because as I understand it they’re pre-gapped. Would this affect gas consumption?


Thanks

auto is killing your gas mile LOL. The other day I went to napa, and they have the list that how to save gas

change 02 sensor ( save 40% on gas )
DRIVE SLOW :grinyes: ( save 30% on gas )
change spark plug and wire ( I forget what the % is )
air filter ( ???? )
fuse filter ( ??? )


you should regap the spark plug, and drive slow, dont let the rpm pass 2.5k. check your tire pressure.Alligment front and rear wheel. again drive like grandma ( I havent seen old people went to gas station that much :grinyes: ).

I was getting about 220 miles a tank before my rebuild and big mods, just imagine what it will be now lol

Yea a full tank, I'm about 200mi/tank in city driving.

That much mileage per tank is apparently normal..don't feel bad because I'm getting like 145 per tank..driving conservatively

why ya'll alway fill up full tank of gas for ?. That take more weight and the car will burn more gas, I alway fill haft tank, or 3/4.

You actually don't want to dip into the lower levels of gas Killer7 (least not everyday driving). There is alot of muck and shit that can be in the bottom of the tank, and you want to stay away from it.

Get a real number for gas mileage, not the number of miles you get on a "tank". The gas gauges in these cars rarely work correctly, so chances are on your 200 miles you are only using like 10 gallons or something instead of the full 16 of the tank. Fill up, set the trip odometer, drive it low (or until the guage says your low), fill it up again at the same spot as before, and see how many gallons you actually put in and divide the mileage by the amount of fuel. This will give you a real number to compare to see if you actually do have a problem.

What size of tires are on your rims? If the overall size is smaller than stock then you are actually traveling more miles than what your odometer says. That could be part of the problem. It may say that you have only gone 200 miles when actually you could have gone 250. The mileage in my RS is like 2,000 miles off because of this reason. And do what |_eclipse_| suggested to help get the real mileage.

Do what | eclipse | said. But you don't have to fill up at the same spot. :confused: Just zero the odometer at the pump, fill it up, and when you fill up again (more miles traveled between these fill-ups will increase the accuracy) write down how many gallons the pump put in (it will say on the pump). Divide miles on the odometer by the gallons on the pump.

If it's still around 13 then there is something very wrong, or you are constantly flooring it. I get 24 average. You should probably be getting more than me.

Spark plugs are supposed to come pre-gapped but they can be off. Just check the gap with any feeler gauge (preferably not the round disc). You can get them from any auto parts store.

And with smaller tires I thought you would put more miles on the odometer than you've actually traveled. Like with my 215/40/17's rather than the stock 50 series, when my speedo says 60 I'm actually going 56. So if it thinks I'm going faster then I really am then it must think I'm traveling more miles than I really am. No? The difference in diameter on my car makes a 6.6% difference on the speedo so if it makes the same difference on the odometer, I should be getting 22.4 mpg (or 26.6 if it's the other way around). So not that big of a difference with smaller/bigger tires on the miles.

Just for kicks, for you to experience a 10 mpg difference (normal 23 mpg to your 13), you would need to jump from 12 inch rims to around 25 inchers (although the added weight would effect the mpg too). And when your speedo said you are going 60 you would acually be going about 30 mph.:rofl: http://www.miata.net/garage/tirecalc.html So I don't think the rims are doing it, unless they're made of lead. :)

Get a real number for gas mileage, not the number of miles you get on a "tank". The gas gauges in these cars rarely work correctly, so chances are on your 200 miles you are only using like 10 gallons or something instead of the full 16 of the tank. Fill up, set the trip odometer, drive it low (or until the guage says your low), fill it up again at the same spot as before, and see how many gallons you actually put in and divide the mileage by the amount of fuel. This will give you a real number to compare to see if you actually do have a problem.

I did that ;) a few times. Still around 220 a tank. I also have run my car right out of gas before :rofl: . But would never do it again

Thanks for the feedback guys, it’s greatly appreciate it. To answer a few questions,

Killer7: I changed the front 02 sensor two weeks ago although I have the suspicion that the mechanic did not reset the ecu which I will be doing this weekend. I don’t speed. I have previously replaced my spark plugs and wires although I will re-gap them just to make sure they’re gapped correctly. The air filter was also changed along with the fuel filter and pcv valve. You mentioned changing a fuse filter but I never heard of that, can you elaborate?

GSX racerGuy: I don’t think 200 miles to a tank is normal. According to specs we should be getting much more than that., 21 city miles per gallon times 15.9 gallons estimates at around 330 miles per tank.

Eclipse & Nayr747: On my original post I wrote down what you mentioned, “Currently I’m consuming about 200 miles per tank which is roughly about 13 miles per gallon”. 200 divided by a 15.9 gallon tank is roughly 13 mpg. I have been setting the odometer every time I fill up the tank for the past several months. Btw, believe me guys I don’t floor it. I drive like a b@tch, with car insurance and tickets being as expensive as they are.


Gthompson: The tire size is 215/40/18, I dont think the fuel consumption would be that significant for this tire size.

Fuel filter. ( my bad )

BTW, whats the correct way to reset the ECU? I've read several ways,

1. unplug the negative battery cable for 5-10 minutes?

2. unplug the negative battery cable for 5-10 with the car idling and hit the brakes a couple of times. Then reconnect and let the car idle for a while?

3. unplug 10A fuse by fuse box located near the brake/gas pedals for 5-10 seconds?

Being that the car does not automatically give a signal or sign that it was done correctly, can someone please set the record straight on the correct way to do this without a datalogger?

toicy: When ever I unplug my battery for about 20 minutes it losses it's settings on my gst. I can tell after because the car runs like crap. As in it's idle is around 200 rpm, but it won't stall. After about 40 miles of driving it goes back to idling around 600rpm.

So I can assure you it does work on mine that way.

BTW, whats the correct way to reset the ECU? I've read several ways,

1. unplug the negative battery cable for 5-10 minutes?

2. unplug the negative battery cable for 5-10 with the car idling and hit the brakes a couple of times. Then reconnect and let the car idle for a while?

3. unplug 10A fuse by fuse box located near the brake/gas pedals for 5-10 seconds?

Being that the car does not automatically give a signal or sign that it was done correctly, can someone please set the record straight on the correct way to do this without a datalogger?

Do not do #2. Ever.

Do #1.

Eclipse & Nayr747: On my original post I wrote down what you mentioned, “Currently I’m consuming about 200 miles per tank which is roughly about 13 miles per gallon”. 200 divided by a 15.9 gallon tank is roughly 13 mpg. I have been setting the odometer every time I fill up the tank for the past several months. Btw, believe me guys I don’t floor it. I drive like a b@tch, with car insurance and tickets being as expensive as they are.


But do you use the entire tank, down to the last drop? Maybe I'm wrong but it just seems more accurate to do it by the exact gallons the pump puts in (has to be exact because you're paying for a specific amount and they can't just jack you). When I do it this way it's very consistent.

My car runs like crap too when I disconnect the negative battery cable, even for just a couple mins. It stalls at every light for at least 30 miles.

But do you use the entire tank, down to the last drop? Maybe I'm wrong but it just seems more accurate to do it by the exact gallons the pump puts in (has to be exact because you're paying for a specific amount and they can't just jack you). When I do it this way it's very consistent.

My car runs like crap too when I disconnect the negative battery cable, even for just a couple mins. It stalls at every light for at least 30 miles.

I think it would be impossible to use the entire tank, down to the last drop without risking getting stuck somewhere without gas. However recently since I've been keeping track of my fuel consumpstion, I do run it for about 20-25 miles after the the gas light turns on.

I think it would be impossible to use the entire tank, down to the last drop without risking getting stuck somewhere without gas. However recently since I've been keeping track of my fuel consumpstion, I do run it for about 20-25 miles after the the gas light turns on.

I usually have atleast 4 gallons left when my light comes on...when my guage says E, I know I still have like 4-5 gallons left. That's just the way the guage is.

do one G's have the same holding capactiy for gas as 2 g's

I usually have atleast 4 gallons left when my light comes on...when my guage says E, I know I still have like 4-5 gallons left. That's just the way the guage is.


Your right eclipse I just tested that several minutes ago. Yesterday my gas light went on, I proceeded to drive for another 30 miles with the light on. I go to fuel up my car today (sunoco regular unleaded) and it filled up with 13 gallons of gas, I guess it still had a little over 2 gallons of gas left. My odometer read 230miles since I last filled the tank. I guess that means I drove 230 miles on 13 gallons of gas which I think would equal to roughly 18mpg city.

I guess my next question would be, Is there anyway I can fix the gas light so that it lights when there's only 2 gallons left in the tank as oppose to 4-5 gallons?

That procedure makes no sense to me (the one to check your mileage).

If you simply divide the gallons bythe miles, how does that tell you anything because for that to work, you would need to fill up the second time starting at the exact same level that you filled up from the first time.

That procedure makes no sense to me (the one to check your mileage).

If you simply divide the gallons bythe miles, how does that tell you anything because for that to work, you would need to fill up the second time starting at the exact same level that you filled up from the first time.

I will try to explain it better...

1. Fill the car up full
2. Set the trip odometer
3. Drive the car until empty (or really close, the more gas use the more accurate this is)
4. Fill it back up full.
5. Take note at how many gallons you put in when you fill up. It should say right on the pump under how much it cost.
6. Take the number of miles on the trip odometer, and divide that number by how many gallons you just put in at the pump. This is you mpg for that tank.

Yes that does make more sense, thank ya. Only thing is I never have enough to fill up all they way...so I fill up with a quarter tank left (I never go below that)..and then I fill up to half tank..then I get 21 miels exactly each time.

BUT..wouldn't it be easier just to go off the capacity of your tank? If your tanks is 10 gallons..and you fill up all the way....you have about 10 gallons (maybe a little less). If you drive 150 miles like me...you will be almost empty...and then just divide those miles by your capacity?

BUT..wouldn't it be easier just to go off the capacity of your tank? If your tanks is 10 gallons..and you fill up all the way....you have about 10 gallons (maybe a little less). If you drive 150 miles like me...you will be almost empty...and then just divide those miles by your capacity?

The problem with that is you will never use the full capcity of your tank, unless you run out (which is not a good thing...ever). That is the only real accurate way of telling your gas mileage, because it incorporates the amount of gas you ACTUALLY used and how many miles you were able to get on that amount of gas, and has nothing to do with the shitty gas guage and the lies it tells you.