I have a 2004 with 65k miles, 6MT, and I installed a Series II fuel pump assembly about 10 months ago. The Series II pump assembly was purchased off of Ebay and was used. Within two months of installing the pump assembly, I needed to replace the fuel filter sock after experiencing fuel starvation at high RPM. This was my fault as I installed the used pump assembly without first checking the fuel filter.

Car ran great until three weeks ago. It was then that I started having high RPM starvation / power loss again. I pulled the pump assembly and cleaned the sock filter, then reassembled. Still had high RPM starvation. I then found that the hard plastic fuel supply line that connects to the top of the fuel pump assembly had a kink in it (Series II assembly port is at a slightly different angle, and over time this caused a hard kink). I cut out the kink and replaced that section of line using high pressure fuel hose and worm clamps (I kept the factory snap connector).

Here is where the weirdness starts.......

After reassembling with with the new section of fuel line everything seemed great. No more starvation at high RPM.....car pulled great. That is until I reached a 1/4 fuel tank level. It was there that I experienced starvation again, and eventually stalling. I pulled the pump assembly again thinking that maybe I have the in-tank supply line caught under the fuel float...keeping the float stuck at 1/4 level and just running out of gas. That was not the case as there was still 1/4 fuel in my tank when I pulled the assembly. I then rerouted the in-tank line counter-clockwise out of the pump assembly, to make sure it wasn't interfering with the float sensor. Reassembled and still experiencing the sensation of running out of fuel at 1/4 tank. After adding fuel past 1/4 tank, the car runs without issue.

I am guessing it has something to do with the syphon assembly on the passenger side, but I am not sure what would cause this.

Whevenver I get near a 1/4 tank and I experience the starvation, I can just do a quick right hand jerk to the car to slosh more fuel on the pump assembly, and I can get a few more miles until the starvation comes back.

This Saturday I plan on pulling the pump assembly again, and also the passenger side syphon assembly. Is there a way to test the syphon assembly?

My apologies for the long post, but I thought the history behind the issue could possibly show a different problem than the syphon assembly.

 

Usually the fuel would mostly be drawn into the drivers side tank. ...so I'd you are having issues with it on the street...the siphon would be a good place to stare. one of the most common problem with the siphon is low pump output. So if you pump is weak that will be an issue

 

Which side of the fuel tank is lower? Is it the driver's side or the passenger's side? If the passenger's side is lower, and the syphon is required to get the last 1/4 tank, then I guess that would point to the syphon system.

It also possible that I reassembled the pump assembly incorrectly, and caused the syphon system to stop working. Maybe a gasket or seal is not allowing a vacuum to pull the fuel from the syphon assembly?

Hopefully I will figure this out when I tear into it tomorrow morning.

 

Both sides are the same level.....the siphon or sloshing is the only way fuel comes back to the drivers side.

 

What is really confusing me is that my float sensor reads 1/4 tank, and the last time I pulled my pump out I still have about 2-3 inches of fuel in the bottom of the driver's side. Wouldn't the pump assembly still be submerged at that depth?

 

Check that the small inlet hole for the pump "cup" is opening. It should let fuel into the cup at that level. If you have 2-3 inches of fuel you should have fuel in the cup

 

Is the small inlet some type of check valve? Remember I have the Series II pump assembly.

 

There has to be a way for the fuel to fill the cup...so look for it and make sure it works 😊

 

On the S2 pump assembly there is a small flapper device on the inside where the inlet comes into the cup. It swings open to let fuel in and closed to slow/prevent it from going back out. I took a few pics a while back when I disassembled a new one, but they're on my PC.

All my hoses and fittings arrived today for my fuel setup. My intention is to put the S2 pump on the passenger side for feeding the engine, use the S1 pump on the driver side to pump fuel over directly into the S2 fuel pump cup, and eliminate the siphon function. Think I may have a strategy where the S1 pump will only run based on the level sensor on that side detecting a certain fuel level.

 

Thanks for that explanation Team. When I pull the assembly I will be sure to make sure that flapper valve is functioning.

 

Since you have to modify the S1 siphon transfer hose to fit the S2 pump assembly housing due to the different fitting size that might be a good place to check too.

Here's a pic of the flapper valve inside the cup:





S2 Fuel Pump Assembly - fuel inlet flapper valve

 

Thanks for the info Team.

Found the problem, and part of it is my failed investigation. The level sensor is faulty, and I didn't catch it before somehow.

Thanks for the help everyone, and sorry for the dumb wild goose chase. I ordered a new sensor and will update the thread after confirming that the problem is fixed.

 

At least you figured it out.