whudini3000

iTrader: (1)

I really need some thoughts on this. I just recently replaced the stock 2004 TL battery that croaked over the holidays with an Interstate 85mo. and I'm noticing better mpg. My driving is mostly city and for the first time I've gotten 180 miles on a half tank with the new battery. Same route, normal traffic.... what gives? I used to get 150mi on a half tank on average... As stupid as this sounds, Trip A is touting 180mi.

rully1012

iTrader: (1)

believe it or not i noticed a jump in mpg also but never related it to the battery... but now that i think of it i started getting better gas around the same time i replaced my battery...hm mm interesting

Kid Fresh

How much did you pay for the interstate battery?

jwr0ng626

iTrader: (1)

wth im gna change my battery if this works hahah

TheChamp531

iTrader: (3)

Impossible unless its a lightweight battery. What you're noticing is the ECU being reset.

whudini3000

iTrader: (1)

$108 @ Firestone w/ $10 coupon from their website

qurious9ss

Yup the ECU was reset and this in turn resets the MPGs on the car. Try this right before getting on the highway for say a 100 mile trip where you'll average a steady speed on cruise control. Once your at the speed your going to travel for the trip, do a reset on the MPGs and you'll probably see an average of ~35+ MPG. This speed for me eventually averages out to 31MPG after the trip and this is the interesting part. The cars MPG average will stay around ~28MPG for weeks after wards, and that's with city driving. Now if I do an MPG reset without being on the highway then my MPGs will average ~25MPGs after a few weeks of city driving. So its not the car getting better MPG, but the car getting a reset and now getting a different calculation that makes it appear to be getting better MPGs. In the end it will all average out.

jwr0ng626

iTrader: (1)

yea..too good to be true

whudini3000

iTrader: (1)

Makes a lot of sense and thank you for putting this in perspective....

jwr0ng626

iTrader: (1)

hmm but didnt u say u got 180 on half a tank compared to 150? maybe ur driving habits changed a lil? weird..

Steven Bell

iTrader: (2)

Very interesting stuff.

rully1012

iTrader: (1)

well im actually a fan of the ecu reset and do it often .....but for some reason out of no where i started getting 30 miles a tank more(till this day i still average the 30 mpt more) i always use the same gas and same oil all the time . after reding this thread i remebered it was around the same time i replaced my battery

maybe im smoking? i dunno but ill take it 30 miles per tank is ligit!! how ever the hell it happened

Souljah

Doesn't make sense, but a lot of things in life doesn't.

Ruby

Duralast can improve your MPG's by 2 in the city sometimes

Turbonut

iTrader: (1)

That certainly is a stretch, but if the battery is weak and the alternator is constantly working to keep it charged, that can affect MPG, but I would certainly believe it would be negligible. Ever listen to some engines, especially the 4 bangers at idle in drive, put on all the electrical loads possible and the engine will slow down as power is required to turn the alternator under load.

01tl4tl

not a stretch at all- you pegged it
Weak battery makes the alt work at max all the time- that takes HP to run, lets call it 5hp to have a number--some race cars might even disconnect alt before short races to make more power!

all the sensors for fuel injection and engine control have very specific voltages they operate at,,drop the supply voltage and get messed up signals = false codes etc

when the neg cable was removed from batt it forced an ecu reset- so any bad driving habits get erased and the car checks all the systems and recalibrates itself
Takes a few tanks for that learning curve to happen

now ck tire pressures--good for 1mpg in many cars

seafom in the gas at a, 16 oz can to 8 gallons gas--just under half tank will clean injectors,piston tops etc and does wonders for fuel mileage,,as well as overall running

need to clean the TB air plate too,,pcv shoots oily crud at it-- all the time engine is running

I hate cars

I agree with this. Sensors, injectors, everything can get "lazy" with low voltage. Plus the alternator has to work harder all the time which draws hp.

You can imagine if the alternator has to draw .5hp more than normal over the course of 250 miles, it can easily cost a few mpg. According to the numbers listed eariler it's about a 3mpg difference which is more than .5hp but this estimate is also to 1/2 tank which can vary wildly. It's hard to see 1 gallon difference on the fuel guage which can account for 30 miles.

Turbonut

iTrader: (1)

They aren't going to get lazy if the system sees 12 volts, whether by battery power or alternator. Years ago you could run a car without a battery and it would run just fine with alternator voltage.

I hate cars

A newer car will not run at it's best at 12v and usually weird things will happen like random trouble codes. I've seen them lean out quite a bit on just battery power. Just about any EFI car needs the alternator to function right.

Turbonut

iTrader: (1)

Not to start a debate, but when the engine is cold and first started there is only maybe 12.4 volts available and the car will start fine, as the alt. is needed to keep the battery charged. Now if the battery is shorted, or can't hold a charge, or the alt. can't keep the battery charged because it's ineffective, bad alt or reg, than the electrical system will have trouble functioning normally.

I hate cars

I think we're saying the same thing lol.

I've wondered before why some cars run weird on full battery voltage but without the alternator. There's the obvious fuel pump and pressure if the car is borderline already. But I've had cars develop a hesitation and I guess lazy is the best way to describe it without the alternator. Many sensors run on a 5v reference which should stay constant regardless of whether it's running on 12v or 14v.

I've even run a "volt booster" that kicked in at 10psi boost. It bumped the volts up to 16v. At night time it looked like you were flashing your brights at someone and hitting the brakes in the rear. It enabled me to stretch out the stock injectors and FP a little further. The car just felt peppier with it.

LaCostaRacer

I'm wondering if the MPG improvement is caused by relearning when running with the winter formula fuel? Certain parts of the country begin using Oxygenated fuels which will cause the mileage to drop a little from Nov-April in some parts of the country. Perhaps doing the ECU relearn procedure tunes the motor with the new fuel characteristics so it runs better with the fuel?

Might be a stretch on this, but I'm sure a stronger battery helps keep the load off the alternator especially for short-trips where there was a big load starting the motor in the first place. If it's a fuel formula thing, you might need to do an ECU relearn each time the clocks change +/- hour to keep the engine at its happiest state of mind.

TheChamp531

iTrader: (3)

I still don't see how it increase gas mileage. I thought the Alternator controls the engine and all electrical components once started.

I'm sure that the reason why the gas mileage is "higher" is because the ECU is reset. I've asked around and this is virtually impossible.

818steez06

damn 30 mpg i wish i get like 22-23mpg maybe its my driving behavior. im gonna change my battery now lol

TheChamp531

iTrader: (3)

^He didn't say 30MPG he said 30 miles more a TANK. And he said that was from a ECU reset. Learn to read? :/

818steez06

my bad no need to get nasty read it wrong

TheChamp531

iTrader: (3)

I'm kidding. I love you. Free lap dances whenever you want

Turbonut

iTrader: (1)

We agree. Just an FYI-The RX7 Turbo we have runs just the fuel pump at 9 volts, but under full throttle the relay will then supply 12 volts. By the way, that's factory standard on the car.

I hate cars

That's pretty neat. That would probably cure some of the issues I have with overwhelming the fuel pressure regulator which I ASSume is the reason Mazda did that??