Need help with a fuel issue!

[911scfanatic]

I was left stranded in my '68 a few weeks ago. A few hours after I had driven the car, I started it up, let it warm up for about 30 seconds and then drove off. Less than a minute after I drove off, the car was chugging and stalled like it was starved for fuel. The pump was a very old aftermarket pump in the factory (engine bay) location. When I got out I noted that there was no fuel pressure, pump very hot to touch and clicking and vibrating like a jack hammer. Pump had been getting progressively noisier over the last 3 months. Fuel pressure was regulated to 3 psi. I concluded (and later confirmed) the pump was bad and replaced it. Half way home from replacing the pump, same thing. I put 2 gallons of fuel in the tank thinking it was low. Started it back up, and that seemed to solve the problem.

I filled up my tank on the way into work today. After my car sat several hours, I started it up and let idle for ~1 minutes. A few minutes into my drive, my car chugged and stalled again feeling like it was starved for fuel. I keyed it up and it showed no fuel pressure. Waited a few minutes and keyed it up again and it showed 3 psi. Drove it back to the office.

What gives? Vapor lock? Debris in system? Please help me diagnose this!

[TargaFlorio]

Had the same issue on my car. Turned out to be debris in the fuel tank. With the fuel level low I took off the sending unit and peaked into the fuel tank with a flash light, I couldn't believe how much rust debris there was floating around. Flushed out the tank with the POR-15 system and never had an issue since (also replace the entire rusty fuel lines).

This might be conjecture on my part, but sometimes a noisy fuel pump can also mean an empty fuel pump. If you have debris in your fuel line that is blocking fuel from getting to the pump, the fuel pump is 'starving' and making quite a racket. Also, the pumps don't like to run 'empty', they overheat and break.

Cheers,
n.

[911scfanatic]

Assuming debris, what is the failure mode? Debris clogging the line blocking fuel flow? Physically jamming the pump, preventing it from rotating?

[TargaFlorio]

Depends on where the debris is coming from. It could be that the fuel strainer is clogged inside the fuel tank. This would lead to low fuel pressure/interrupted fuel flow.

Or somewhere along the fuel line, the metal fuel lines have rusted and debris is causing low fuel pressure/interrupted fuel flow.

After 40 years it could be a culmination of both.

There's a fuel filter before the fuel pump that should pick up most of the debris. Install one after the pump as well. I don't think that one foreign object could get past the fuel filter and prevent the pump from rotating. But over time enough sludge could cause the fuel pump to fail or get stuck.

In my case it was debris that was causing low fuel pressure.

n.

[B D]

I would just pull the line after the pump and let it run a few gallons in to gas can watch for any interruptions in flow or pump noises. My guess is a clog at the tank. There is metal line running through the car so it's either at the tank or in the engine compartment.

There is a small screen around the fuel pick up in the tank that may be clogged. On a 68 there is just one outlet for fuel with no return, there is a drain plug next to it. That outlet connects to the metal line with a small length of hose and exits in the engine bay.

[RSTarga]

your filter at the tank is clogged, remove it clean it and replace

[911scfanatic]

Alright, I have the sender out so I can see inside the tank. There is some debris (rust flakes mostly) at the bottom of the tank. The screen itself looks fine.

I have been draining the tank about 2 gallons at a time (using the fuel pump with my 7 yr old working the ignition key). So far after about 5 gallons the pump has run smoothly and the screen does not appear to be clogging.

This leads me to believe that if it is the screen, the screen is only getting clogged during driving as the debris gets kicked up and sucked into the screen. This is consistent with the car starting after I let it sit for about 5 minutes. The debris probably fell off the screen and settled back at the bottom.

If that is true, then cleaning the screen will not improve the problem since it is the debris that is clogging the system. Then, the only solution is to drain the tank and get it flushed. I will install a new screen at that time and blow out the gas line.

Agree?

[TargaFlorio]

I used this stuff from Por15

http://www.por15.com/FUEL-TANK-REPAI...ductinfo/FTRK/

Very easy to use and never had an issue since.

Cheers,
n.

[Neil '67 911S]

Before you treat the tank, drain and rinse it well with hot water. I poured in a handful of 5/8" nuts and shook the heck out of the tank, flipping it all around while shaking as hard as I could. Pour out whatever nuts and loose rust you can from the fuel sender port and the neck of the tank. Go after the rest through the fuel sender port with a vacuum cleaner.

If you do decide to go the POR-15 gas tank sealer route, a critical step for success is to dry the tank completely after being rinsed with water following the draining of the second requisite solution (Metal Ready). After draining as much of the rinse water as possible, place the tank upside down so that the fuel sender port lies flat on a board and fuel, gas heater and drain ports are up, nearly parallel to the plane of the board.

Borrow your girlfriend's/wife's/daughter's Conair Model 247 1875 watt hair dryer and attach it to the fuel filler neck of the tank with a hose clamp. The two are the same diameter! Put the hair dryer on the lower setting and walk away for a day. The tank will be bone dry and ready for the POR 15 fuel tank sealer.

Seal up all holes with masking tape, except for the filler neck of the tank. Pour in the POR 15 tank sealer solution and masking tape this hole shut. Since the tank will still be warm, the POR solution will spread easier than if the tank is cool.

Turn the tank over and over until you no longer hear any sloshing. Now let it languish with each of the six sides down, this includes the top, bottom, front, back and sides, for a good 15 minutes per side. Remove the tape from the fuel sender hole and with a good flash light, check on the progress of the spreading. It will be apparent what has and what has not been coated. You can watch how the rather viscous POR liquid advances quite slowly. Re-tape the tank and flip it some more to let the solution spread well.

Drain the excess and discard. Clean up the threads of the fuel outlet ports with a rag. Re-attach the hair dryer and blow dry the POR 15 tank sealer dry. I plan to paint the two tanks I've treated with POR 15 paint followed by grey Wurth Stone Guard once I'm done giving final exams.

[berettafan]

the idea is the suction pulls the crud against the screen thus blocking flow. blockage releases when suction stops.

had the exact same issue with my car but really don't believe it was screen related. replaced the tank, lines and pump and all is well.