Ok, I can't figure this one out. I have a 2000 Accord EX I4 F23A4, by the way. Lately, when I fill up my gas tank and drive, the RPM's don't seem to climb as much or have less power vs. when there's little fuel in the gas tank. I have a habit of filling the gas tank when it's nearly empty and someone once told me that that will burden the fuel pump and wear it out quicker. Not sure if my habit of empty filling damaged the fuel pump but I digress.

I naturally thought that it might have to do with the weight difference of a full gas tank vs. a nearly empty gas tank, but I know that's not it because even when having another person in the car, the RPM's won't climb as quickly with a full tank vs. a nearly empty tank.

 

Your original thought was correct. Our cars are very weight sensative. Think about it this way. When the tank is full there is about 170lb's of extra weight in the rear of the car, give or take (17 gallon tank). Now when your empty say you have 4-5 gallons of fuel left you have just effectivly taken out over 120lb's of weight. That is a hugh difference in how the car will perform. Not only on acceloration but on braking too.

 

Well, the thing is that sometimes the engine is very responsive even with 3 passengers in the car but with low fuel in the tank vs. no other passengers and a full tunk of gas. When I fill it up with full tank of gas (regardless of having passengers in the car or not), the engine seems to rev slower, about 1/3 slower than with less fuel in the car. So there were situations where I had more weight in the car (2 passengers equalling 400 pounds) with low fuel and a fast-revving engine vs. a slow-revving engine with a full tank of gas and no other passengers. It's weird...

 

If you let the gas tank get near empty, it can start sucking up dirt and what not thats been sittting in the tank, and cause the fuel pump to fail

 

True, but isn't that what a fuel filter is for? Wouldn't it get filtered before it gets to the pump? Or is the filter after the pump?

And how would I go about testing the fuel pump? Could I get an OBD-II scanner and look at its values to see if it's out of range? Or do I have to just replace it and hope that it was bad? Thanks!

 

do you get your gas at the same station each time? Some stations suck! it could be humidity in the air.

 

If you run the car with a low fuel tank you better start looking for a new (Fuel pump, filter, maybe cleaning the injectors) When you run low in gas and every time you make a turn the fuel pump starts sucking air and the pump will start to fail, that is the best way to damage it.

 

I understand the logic but if the fuel pump is bad, why would I get more power and better throttle response with low fuel in the tank? I should have low power and not-so-good throttle response regardless of the amount of fuel in the tank, right?

 

The pickup is sitting in the same spot regardless of how full the tank is. Any sediment that is in the tank still sits on the bottom regardless of how full the tank is. You are always drawing fuel from the bottom of the tank. I have always run my cars down to the last gallon or two. I've never experienced any of these imagined problems.