My tank was on 20 miles to empty today, and my car in general has been feeling sluggish for the past couple of days, it might have been the weather I'm not really sure.

I go and fill up the tank tonight with 91 chevron( what I always get). And WOW, I really don't think I'm imagining it but it seems like my car is much more responsive and it just feels a lot better than before. DARE i say faster?? It doesn't make much sense to me, since a full tank is a lot of added weight, but it really felt better..

Any ideas on why this could be.. ? Or am I just nuts?

 

Theoretically, the car's faster when tank's empty.....
I guess the reason you feel the car's faster is... you can floor it whenever you like to when the tank is full; when the tank's almost empty, I'm always very careful and easy on the gas, cause I'm afraid the car will die on me... maybe that's the reason?
I'm not sure

 

I asked about this before but nobody replied. My concern is that if our ECU is like the one in some Porsches the car will actually adjust the ECU to restrict performance in order to save gas. Problem is that sometimes the ECU can reamain this way....at least thats what happened to my friends 99' 911. Porsche dealer had to reset it.

 

I have noticed this too. I think it may retard the TB opening speed when fuel is low.

 

Weight distribution changes when car is filled. 20 Gal of fuel is atleast more than 120 lbs, that would be more than 5% of weight shifting.

Thus when car accelerates, more weight and grip is applied to the rear

 

my Maxima feels really smoother and faster after a full fill up. I dont think you are imagining it in your head. I think the ECU restricts something when the fuel is low.

 

In NASCAR races, theoretically, the car stops when the tank's empty.

j/k sorry.

WayneTN

 

I felt this way driving my old integra. I didn't say anything to anyone because I figured they'd think I was crazy.

 

Correct regarding restricting performance to conserve gas. However, it doesn't put a "cap" on performance. It just retards the timeing and what not, because if you are damn near flying on fumes and want to gun it. The car will fly. It will just take a while for the computer to decipher not to save gas and let this bonehead run dry. It is quite a noticeable lag before it makes the adjustment. I did not know about the ECU getting stuck and remaining that way. Hmmm... my car has been feeling sluggish as of late.

 

*repost deleted*

 

I agree . It's all in the mind .

PEACE!!

 

Maybe you got a bad tank of gas. If you get gas right after the truck unloads it you get some water in your gas. Happened to me in my Saleen and the car simply would not run. Siphoned out all the gas, filled back up and the car ran perfect. If you see the truck at a gas station dont get gas there go somewhere else. I was lucky it didnt ruin my car....

 

I've noticed the same on my teg.

Has it anything to do w/ the fuel pressure?

 

interesting....

maybe it IS in the head, but i've noticed it too...

 

The increase in power might have to do with the change in weather tempertures. Gas companies have to have different additives in their gas according to the temperture in that local area to give the gas more ideal combustion properties. So basicly, if the weather turned much cooler over a few days and you still have "summer gas" in your car, then you go fill up on a new mix of gas for winter, then yes, you might actually feel a difference.

The gas in the tanks under the gas stations also collect water over time. The deleivery drivers that refill your gas stations have to monitor this everytime they make a delivery. Then they add more additives to the gas to make up for the extra water. So if you fill up at a station that doesnt have alot of buisness, chances are the fuel they have isnt as good as another stations that has much better buisness.

I use to be a night clerk at a Texaco. 8-)

 

The z tank is right behind the seats, in front of the rear tires. The weight shift wont make that big a difference, but the initial fill up will.

 

it makes sense to me that the ecu would restrict performance some how when it senses the car is low on fuel, but does anyone actually have any backing to that statement...or is it purely a guess..

better yet is there a way to stop the ecu from doing this?

it seems as if my car felt sluggish for a while, maybe the last 60-70 miles on the tank.

even this morning after warming it up it didnt feel the same as last night..

 

Here is my attempt to sound like I know what I am talking about.

FACT: The amount of fuel supplied to the engine is determined by the amount of time the fuel injector stays open. This is called the pulse width. The pulse width is controlled by the ECU. How does the ECU determine the pulse width?

The engine control unit uses a formula and a large number of lookup tables to determine the pulse width for given operating conditions. The equation will be a series of many factors multiplied by each other. These factors are given to the ECU from the thousands of sensors such as the airflow, engine temperature, engine speed, throttle position, etc. So the pulse width would directly be affected by the readings from these sensors.

That is all for the fact part. But I am willing to bet that there is a fuel level sensor that provides input to the ECU to determine the pulse width. What percentage of the formula is affected by the fuel sensor reading... that I do not know. I haven't made it through the entire ESM and most of it is greek to me, but it might list the sensors that affect the fuel injector system.

That being said... I always listen to what my butt dyno says! Ignorance is bliss!

 

I feel the same way, after a fill up, this car is like, ZOOM....haha, I was like to "feed her up some nice fuel before I go out on the weekends..."

 

Fresh gas usually have slightly higer octane than old gas. That might account for better performance.