I have a 408 in a 67 nova with twin turbo's. Car runs great when it is not super hot. Go for a drive 250 miles above 90 degrees outside) and the car feel like it is out of gas. Replaced the pump with a magna fuel tuner pump(good for 1500 hp) and the car still does the same thing. If the tank is full no problems gets around 1/2 a tank when it is super hot out and it will act up. I have ordered a sumped tank to run lines out the back of the car?? The pump is mounted pretty close to the passenger tail pipe top bend. I have wrapped the tail pipe bend with header wrap and it is the same???

 

Take your gas cap off and see if the problem goes away. If the return line is clogged air will not get back into the tank as the gas is removed by the pump and create a vacuum in the tank to stop gas from flowing to the engine. By removing the gas cap it will let air replace the space created by the gas being pumped to the engine and prove the problem of not adequet gas tank venting.

Other checks:

• crimped vent line
• fuel pump pressure low
• if external fuel pump it must be lower than the tank
• Fuel tank must have baffles to keep gas on the pump during driving

 

Ok, I finally got the car back together. I rented a bottle of nitrogen to fill the empty gas tank so I can weld on the new vent line for filling. I used a 3/8" steel brake line and bought a second short line to remove the threaded ends that I drilled holes in my tank and filler neck then welded on those threaded ends. I then used the second line and some brass couplings to connect to the welded threaded ends and the new line between. I thought it would be cleaner and allow me to remove the line should it be in my way during installation. I was so nervous to weld on the gas tank that I initally had my welder too hot and burned a hole in my gas tank. I had to stitch that hole up and continue to weld on the threaded fittings. I suck as a welder due to my lack of practice so my welds look like gorrilla welds. I have a pin hole leak on the fitting welded to the tank just above the filler neck joint. I will go get some JB Weld and coat that area to seal up that leak. I think this vent line will now solve the gas splashing out the neck while filling up the tank causing me to fill it slowly. Now I should be able to fill it up fast.

Looking inside of the this new FI tank the filler neck extends to the back part of the tank through a large baffle. It contains a smaller diameter vent line about 1" in diameter at the top exit inside the tank which I assume was suppose to allow the air to vent. This apparently doesn't work or I would not have to add this vent line as so many others with aftermarket tanks had to do. The filler neck looks to be slightly angled up inside the tank which would allow the fuel to pool up at that low part in the neck which is probably why the fuel backs up while fueling.

My old fuel pump was the new style Walbro. It was still working but with low pressure so I used it to pump most of the fuel out of the tank into gas jugs so I could drop the tank. It has always been very noisy with a high pitched wine that I could hear over the radio even. This new Walbro pump is a lower pitch and a lot quieter. I never verifyed the fuel pressure of the old pump so I don't know if it was correct to begin with and went bad or it was originally weak and just got weaker.

I blew through my original vent line from the tank to the charcole cannister at the front of the car that I retained and connected to the LS1 and I could get air through it but with a great amount of back pressure. So I purchased over 20 feet of standard fuel line and tie strapped it along the same vent line from the tank to the charcole cannister. I reused the shorter vent line at the tank that originally had a rubber hose between it and the main vent line that ran along the frame rail. It made connecting the tank lines back up easy. I will replace the frame vent line when I pull the frame to get it powder coated one of these days hopefully by next year.

So I think either the pump was bad to begin with but it did last since 2005 when I originally did the swap. I think the high back pressure on the vent line might have put a higher than normal vacuum on the tank that contributed to the failure of the fuel pump. The pump must have overcome the partial vacuum for awhile before it cause the pump's premature demise.

Now I have plenty of power. I didn't notice how much power I was missing. The car now runs smoother and a lot less vibration. The injectors are less noisy probably because they don't have to work as hard to overcome the low fuel pressure.

I can now get a little more gas into the tank because of the vent line on the filler neck. Now to seal up that pin hole leak in my weld job and I can be completely done with this repair.

Look at one of my previous post for the fuel pump part numbers. The new 340 Walbro inlet is larger and centered on the pump compared to the new style. One can research both of the part numbers to find out what is the differences are and the newer style compared with the 340 and the obsolete 340W (I think or is it M.)

I hope my experience with this problem and my solution helps others. Also I hope others would take the time to not only post their problems but post their solution for all to learn and help solve others issues.

Thank you for everyone for their comments and help, I really appreciate their advice and their experience.

James