Fuel pump failure modes
 

When a Fuel pump fails, or gets to a point where it should be replaced, what are some of the symptoms?

The engine in my car runs great from a full tank, till a little bit past a quarter. beyond that, the idle is lumpy, power is slow and anything but smooth.

I'll put it this way, I can haul ass up a hill in 3rd, with a FULL tank, but at 1/4 I'm downshifting just to maintain 50Km/h.

EVERY tank, and I run 91

Is it possible that my fuel pump is getting weak, and with the added pressure against the pump with a full tank, it works well, but it's ability to deliver the correct amount of fuel pressure diminishes as the weight of the fuel in the tank decreases?

Could be but I'd check the tank strainer and the other filters first

Throw a new pump or two at it. Not hard to do.

Steve

Try leaving tank cap loose to see if you're building a vacuum in the tank.

I just replaced both of my pumps after noticing a subtle rattle/racket sound coming from the rear of the car. After sticking the tip of my stethoscope on the plastic fuel pump cover, it was evident that at least one of the pumps was making the noise. After removing the pumps, I noticed one of them rattled like a gourd when I shook it. I presume this was the bad pump.

Regarding your low fuel tank resulting in a reduced pressure to the pumps, I'm not sure how the input pressure affects the output of the pump, but I will say that when I slid the supply hose off the back of my pump I was surprised at the pressure and amount of flow that came out before I could bend the hose and stop it (my hose crimp tool was not big enough to reach across the whole hose). It was like trying to stop the flow from a garden hose. Unfortunately, I did have a full tank of gas at the time.

Wow! No sooner had I read emrydc8's comment, then driving I smell gas.
I look and the 2" piece of hose between the fuel damper and the pump was POURING fuel, I lost probably a two litres. I was able to catch one... Good thing I had an available shop with lift! :D new hose fixed in an hour.
if this hose was seeping for a while, could the pump suck in air via the cracks in that hose?

If that hose had completely broken, as I was driving, it easily would have cost me THOUSANDS of dollars. Not to repair, but for all the other things that would happen.
First of all, there would be no stopping 90 litres of Vpower from going directly to the ground ($120), but the cost of the call to the FD to handle the spill ($975 call out fee), a municipal pollution fine of $3500 - $5000. and because it's a 2" piece of hose that would have failed, my insurance would not have covered it.....:eek:

.

If you were a corporation, you'd probably get a tax break from our government for the loss of valuable fuel and you would make CNN for your heroic effort to stop the spill because it could have been much worse. As a lowly worker ant, I wouldn't be calling anyone but a tow truck.

Glad you found the problem.