Poor Gas Mileage....

[toicy4ya]

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

[Killa]

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 ( 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 ).

[Talon69]

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

[LouieAWDTSi]

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

[GSXracerGuy]

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

[Killa]

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.

[l_eclipse_l]

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.

[gthompson97]

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.

[Nayr747]

Do what | eclipse | said. But you don't have to fill up at the same spot. 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. http://www.miata.net/garage/tirecalc.html So I don't think the rims are doing it, unless they're made of lead.

[Talon69]

Originally Posted by l_eclipse_l

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 . But would never do it again

[toicy4ya]

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.

[Killa]

Fuel filter. ( my bad )

[toicy4ya]

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?

[nova1313]

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.