No gas coming out of the tank!

[charliekwin]

Hey guys, I'm officially stumped and could use some suggestions.

 

I repainted the tank a couple weekends ago, put everything back together, and can't get any fuel to flow from the outlet.  I put a minimum of 5 gallons in there, so it's not low.  There's nothing physically blocking the outlet; I even blew some compressed air into the outlet, which went into the tank and back out.  Blowing air into the tank does force some fuel out of the outlet, but it doesn't continue to flow.

 

I restored the tank earlier this year and had no such problems the first time.  Nothing was done to the interior when it was repainted, either.  I don't want to drain and drop it again, but I'm rapidly running out of ideas.  Help?

[Patcon]

So you can blow air into the outlet and hear it coming into the tank?

 

You can blow air into the filler neck and fuel comes out or you are blowing air into the return line and fuel comes out?

 

Once fuel flows out it wont continue to come out even with a section of fuel line acting as a siphon?

 

Is the filler cap on or off when fuel won't flow out?

[Zed Head]

 I even blew some compressed air into the outlet, which went into the tank and back out.  

 

Blowing air into the tank does force some fuel out of the outlet, but it doesn't continue to flow.

These two things are hard to figure, especially the first one.  It implies that everything was sealed up except for the outlet port, and that you pressurized the tank and the pressure was released when you stopped.

 

One the second - how did you blow air in to the tank?  Through the return port, or the filler cap, or a vent line?  Not clear.

 

I'd try taking off the filler cap and blowing air in to the outlet port.  If fuel is covering the other end you'll hear bubbles inside and air will come out of the filler hole.  Don't blow too much or you'll the area with fuel fumes.

[charliekwin]

So you can blow air into the outlet and hear it coming into the tank?

 

You can blow air into the filler neck and fuel comes out or you are blowing air into the return line and fuel comes out?

 

Once fuel flows out it wont continue to come out even with a section of fuel line acting as a siphon?

 

Is the filler cap on or off when fuel won't flow out?

 

In order: yes / blowing into the outlet and fuel comes back out / haven't tried leaving the fuel line connected / and does the same -- no continued fuel flow -- with the cap on or off.

 

These two things are hard to figure, especially the first one.  It implies that everything was sealed up except for the outlet port, and that you pressurized the tank and the pressure was released when you stopped.

 

One the second - how did you blow air in to the tank?  Through the return port, or the filler cap, or a vent line?  Not clear.

 

I'd try taking off the filler cap and blowing air in to the outlet port.  If fuel is covering the other end you'll hear bubbles inside and air will come out of the filler hole.  Don't blow too much or you'll the area with fuel fumes.

 

Re-reading my post, I didn't make it especially clear.  I did exactly what you suggested: blew air into the outlet port, heard it go in to the tank and come out of the filler hose; then had a small rush fuel come back out of outlet when removing the air nozzle before it stopped entirely.

 

I couldn't find any tubing that I could use to pressurize the tank through the filler neck, but that's something I could try.

 

One thing I did differently this time than the first: when I dropped the tank this time I clamped off both the outlet and return lines (I didn't the first time, and had a nice gasoline shower).  The first time I also replaced the fuel filter in the engine compartment and put in an inline fuel pressure gauge, which wasn't necessary to repeat.

 

Since there's no pump in the tank, I assume the tank -> fuel pump part is gravity/siphon fed.  Do I need to get that feed going manually?  It all just worked last time; maybe it was just beginner's luck?

[Zed Head]

It sounds like you're just losing siphon.  You might add a length of hose to the outlet port with end of the hose below the fuel level inside the tank and try again.  5 gallons will spread to a low depth in the bottom of the tank.

 

Or you could just connect the pump, put the end of the exit hose in  a gas can and run the pump using the Start trick (disconnect the solenoid).  Maybe you just need to suck some snot through the lines.

[Patcon]

Are you sure there is not a lot of debris in the tank?

[SteveJ]

If you can push fuel out with air pressure but can't pull fuel out with a fuel pump, there could be some pinhole leaks, say in the pickup tube. If you have enough fuel that it covers the leak, you're fine, but once the leak is in the air space, you'll suck more air than fuel.

[Zed Head]

Adding a picture to think about.  If the outlet port tube is tweaked upward, or the car is tilted, the siphon problem, and just keeping the inside hole covered, gets worse.  These cars are known to suck the line dry on left hand turns when the tank gets down around 1/4.

 

 

[charliekwin]

There shouldn't be any debris in the tank (I cleaned and coated it a few months ago); leaks in the pickup are possible but unlikely since they would have had to develop in the last month.

 

I read through the FSM again and it says the pump should be pulling from the tank, so I wonder if that's actually happening.  I'll try DCing the starter and to see if I can figure out what the pump is -- or maybe isn't -- doing.

[Zed Head]

Just disconnect the small solenoid wire at the starter and turn the key to Start.  The pump should get power.  It's actually the method described somewhere in one of the FSM's or the EFI Guidebook.

[Chickenman]

Reading the OP Signature line it looks like he has a 1978 280Z. OP: Is that correct?

 

1977 and 1978 280Z's have a fuel tank that is different than the earlier style that ZedHead shows in post #8. From the parts manual, it looks like the fuel line connections are on top of the tank. OP: Can you confirm this?

 

With fuel lines on top of tank, fuel has to be drawn out by vacuum from the fuel pump. 5 gallons in the tank may not be enough to have fuel flow " up and out " by tilting the tank or even pressurizing it. You would need a very large volume of air to maintain flow, and all vent lines and fuel filler tube would have to be closed off.

 

Picture of 77 - 78 Fuel Tank. Note that the fuel lines appear to come out of top of tank:

 

Edited November 26, 2015 by Chickenman

[Chickenman]

OP: If you do confirm that pump is operating, you may have to add more fuel than 5 gallons to get the fuel pump to prime. You may have an " air-lock " in the fuel line. Since the later models fuel lines are at the top, the F/Pump may not be able to create enough suction in the line to prime itself and start a siphoning action. 

 

It's not a problem with " In Tank " pumps as they will prime with low fuel. But with external pumps, if you lose the prime in the fuel tank to fuel pump line, it can be an issue.

 

If pump works, then fill fuel tank to top. Or have a helper pressurize fuel tank with compressed air while you crank the engine. You will need a fairly large volume of air and you will have to close off the hose to the " Vent Reservoir tank "

Edited November 26, 2015 by Chickenman