Fuel Pump Issue

[PATHFINDER99NI]

Hey all, I hope everyone is having a great day.

I replaced the FP IN MY ‘99 LE a few years ago w an aftermarket unit. It works great, except for the fact that the truck acts like it’s empty at a gauge indicated, 1/4 tank (recently it’s starting to do that around 1/8th tank). When I go fill up, it’s not empty, theres always the indicated level of fuel. What gives?

Thanks for any help.

[VStar650CL]

"Acts like it's empty" in what way? Are we talking about the gauge indication, or the engine? If it's the gauge acting up, you probably have a "dead spot" in the sender where the sliding potentiometer is losing electrical contact.

[PATHFINDER99NI]

"Acts like it's empty" in what way? Are we talking about the gauge indication, or the engine? If it's the gauge acting up, you probably have a "dead spot" in the sender where the sliding potentiometer is losing electrical contact.

My apologies, in my haste to get into Costco, I omitted some info. I fixed it. The gauge indication is correct, but the truck dies as if it was out of gas.

[VStar650CL]

That sounds like your aftermarket pump is overheating. The motor on any in-tank fuel pump is cooled by the surrounding fuel. Most of them use sealed sleeve bearings, and when those start to go south, thermal expansion will often cause them to bind when the tank is near empty. Here's an excellent vid explaining how the various types are constructed and how they work. The first type, or "turbine" pump, is what you'll find in most Nissans, Infinitis, and passenger cars in general:
https://www.youtube.com/watch?v=QbzEeWy1b3o

[mdmellott]

Here's an excellent vid explaining how the various types are constructed and how they work. The first type, or "turbine" pump, is what you'll find in most Nissans, Infinitis, and passenger cars in general:

Thanks for that. It explains to me why I have seen my fuel pump getting weak. I just happen to be right in the middle of replacing my fuel pump right now. My pressure has been at the low end of acceptable for quite some time but has gotten worse slowly over the past several months. Starving for fuel at idle I would see a very brief surge of a couple hundred rpm as, I assume, the ECM opened the injectors longer to make up for the lack of fuel and then the engine speed would drop back down to normal. It has been fine on the highway but recently slow to respond with acceleration. Several other performance symptoms as well all pointed me to a weak pump. I didn't bother borrowing a pressure gauge to check this 22 year old pump since I have never had one last this long in the first place and I got a great price on an OEM pump and gasket out of the UAE for $122.

One of the strangest things I have ever seen when I took the retaining ring off this morning, to remove the old pump, is that the plastic looked all busted up but there were no busted off pieces. After removing the assembly, I can see that the plastic looks like it has dissolved around the perimeter. The gasket sealing surface is just barely all intact. The top of the tank, just at the seating ring, was badly corroded. Not prepared for replacing the level sending unit assembly, I cleaned it all up, scrapped off a considerable amount of rust, and then painted the tank seat with Rust-Oleum. Now, waiting for the paint to dry, I'll put it all back together and hope this old man comes back to life. I hope my Pathfinder still works after this as well.

[VStar650CL]

One of the strangest things I have ever seen when I took the retaining ring off this morning, to remove the old pump, is that the plastic looked all busted up but there were no busted off pieces. After removing the assembly, I can see that the plastic looks like it has dissolved around the perimeter. The gasket sealing surface is just barely all intact. The top of the tank, just at the seating ring, was badly corroded. Not prepared for replacing the level sending unit assembly, I cleaned it all up, scrapped off a considerable amount of rust, and then painted the tank seat with Rust-Oleum. Now, waiting for the paint to dry, I'll put it all back together and hope this old man comes back to life. I hope my Pathfinder still works after this as well.

Wow, that's a new one. Not that cracked-off pieces couldn't bounce their way off the top of the tank and onto the road, but you'd expect to find at least some evidence still hanging around. Can't be chemical deterioration from anything inside tank, either. The portion inside the tank would be destroyed and not the outside flange.

Rodents, maybe?

[mdmellott]

Rodents, maybe?

It does look like something ate it. None of the missing portions are cracked off. Every bit of the edges are pock marked with tiny craters like microbes were eating away at it. The retaining ring covers the entire flange so nothing bigger than an ant could possibly take a bite out of the exposed edges under the ring. After 20 years, things are bound to pop up for maintenance I haven't already dealt with but this is one I couldn't even imagine. It's a weird one for sure.

Got it all back together now. No leaks and it runs like a champ. Maybe I should put some no pest strips up under the body.

[VStar650CL]

Got it all back together now. No leaks and it runs like a champ. Maybe I should put some no pest strips up under the body.

[mdmellott]

I was just reading a couple of science articles about plastic eating bacteria and petroleum eating bacteria. I think there might have been some crossbreeds munching on my fuel pump.

[VStar650CL]

I'll buy that.

Hmm, I don't think sticky traps will work on those....