Preventing vapor lock

[J-440]

I can drive the car for about 20 minutes with about 10 gallons in the car and then she sputters then dies. Let her sit for 10 minutes and she fires right up. Vapor lock. With 5 gallons it takes about 5 minutes and the car dies. Here's the setup: 440 iron block with EFI, jet hot coated headers, Aeromotive A1000 EXTERIOR mounted pump lower than the tank. -10 feed, -8 return, 2 filters, pressure regulator set at 59psi. All lines insulated starting at the header collectors. After 10 minutes of idling, my headers are close to 600 degrees, and the sending line, return line and fuel rails are 250 degrees. Fuel boils at 205 degrees. I'm ordering some header shielding and maybe some fuel rail shielding. Last resort is ordering an in tank pump. I know most of ya'll are running aluminum blocks but do ya'll still have a ton of heat shielding around your motor? And are fuel coolers worth the money? Thanks.

[Oleyellar]

How did you vent the tank? Do you have an adequately sized vent, You could be drawing a vacuum on the tank causing the pump to cavitate.

[BBC71Nova]

Tried a controller for the pump to slow it down? That's a lot of pump and circulating the fuel isn't helping the heat issue.

[dhutton]

Bad choice of pump imho. That pump isn’t built into an extruded aluminum heat sink for no good reason. It generates a lot of heat. Insulating the fuel lines might actually be making things worse if the pump is heating the fuel.

I would get rid of it and go Vaporworx PWM controlled in tank fuel module. You will never look back.

Don

[J-440]

I’ve got a 1/2” vent line from the top of the fill tube exiting through the trunk floor. I’ve also got a fuel pump controller so the pump isn’t going full blast during cruising. Anyone take a temp reading of their fuel rails? Just curious about the differences in iron and aluminum blocks.

[dhutton]

I’ve got a 1/2” vent line from the top of the fill tube exiting through the trunk floor. I’ve also got a fuel pump controller so the pump isn’t going full blast during cruising. Anyone take a temp reading of their fuel rails? Just curious about the differences in iron and aluminum blocks.

What cutback rpm did you set that Aeromotive controller for? What is the reduced pump voltage?

Don

[GregWeld]

One year on the HOF tour we had a Mustang with an externally mounted fuel pump -- fuel would get hot and the car would start acting up or leave her stranded...

Someone suggested filling the truck with bags of ice until a real repair could be done. BINGO --- problem solved.

What am I saying here?? It was all about the pump overheating.... Period. Nothing else wrong with the system.

[J-440]

The controller is set to go full blast at 3500rpm. Voltage is fine. Forgot to mention that the pump temp was at 175 degrees when everything else was at 250.

[dhutton]

The controller is set to go full blast at 3500rpm. Voltage is fine. Forgot to mention that the pump temp was at 175 degrees when everything else was at 250.

So you don’t know what your reduced voltage is? Haven’t you measured it?

If the heat sunk exterior of the pump is 175 you can bet the internal pump components are considerably hotter. If I had to guess I would say in excess of 300 degrees. This is based on 35 years of hardware design and countless thermal analyses and calculations....

Don

[J-440]

Voltage is right at 9. I used the instructions on the Aeromotive website.

[dhutton]

Pretty sure that pump is cooking your fuel if the external temperature is 175 degrees. What is the temperature of the fuel lines connections in and out of the pump? If the output side is much higher than the input side then that would show it is heating the fuel...

Don

[GregWeld]

Just copied off the internet -- not my personal knowledge -- but trying to find something helpful.



Gas doesn't typically "boil", but it does vaporize (evaporate) at anything over 93 degrees F or so. As I understand it, the "boiling point" of regular 87 unleaded is about 181 degrees...but this will differ depending on pressure and what additives are in the gas

[J-440]

I’ll check the line temps. But dam, is this normal for this pump? I’ve got it lower than the tank like Aeromotive said and all the lines are well insulated past the header collector.
Let’s say I use an in tank pump without changing anything. About how cooler would the fuel be? I’ve got some lava header wrap coming in the meantime. It’s more of a do it yourself shield like you see on LS motors. Trial and error I guess. Thanks for all the help.

[GregWeld]

I don't need an answer -- I'm just THINKING OUT LOUD --- so to speak.


Fuel "boils" when under vacuum (suction) --- so since the pump is external to the tank and pick up --- What size is the pick up tube?? And do you have any sharp 90's on the INLET side from tank to pump.... I try to use 90* "sweeps" instead of hard 90's or GO UP IN SIZE on the pick up and plumbing to the pump to avoid that. IDK.

[J-440]

-10 sending and -8 return. The fittings are both at a 45 degree coming from and to the tank. The sending line makes a nice radius above my rear axle, goes around to the side next to the frame rail where the pump is mounted. Just behind the rear tire and under the trunk floor. I have a pre filter, then the pump then the line does a 180 (2 90 degree fittings joined together) to another filter then it’s a straight shot to the fuel rails.

[dhutton]

I’ll check the line temps. But dam, is this normal for this pump? I’ve got it lower than the tank like Aeromotive said and all the lines are well insulated past the header collector.
Let’s say I use an in tank pump without changing anything. About how cooler would the fuel be? I’ve got some lava header wrap coming in the meantime. It’s more of a do it yourself shield like you see on LS motors. Trial and error I guess. Thanks for all the help.

Depends on the pump you use and how you control it. I’ve used several Vaporworx controllers without a hitch. The beauty is the pump never runs any harder than it needs to. Keeps heat to an absolute minimum. No return line to mess with.

Interested to see those input and output fitting temperatures.

Don

[GregWeld]

I might suspect the 180* -- maybe try rerouting that temporarily to see if the issue continues?? IDK -- we're just trying - at this point - to find ANYTHING....

[Che70velle]

I “assumed” that efi wouldn’t allow a vapor lock to happen. I’ve seen guys run fuel lines in some stupid places, like right beside headers and turbos, without a hitch.
What does your fuel pressure gauge say when this happens? Maybe try and pop the orifice at the fuel rail to see if there’s fuel pressure there when this is going on, regardless of what gauge says. Heat is your enemy when it comes to fuel systems, especially with an inline pump setup.

[J-440]

When the car starts to die, the fuel pump starts cutting in and out then it dies. My regulator is at 0 psi. I’ll wait 10 minutes, pressure is back up to 59psi then the car fires up. Gonna get those line temps here in soon.

[Zspoiler]

Have you tried a heat shield under the fuel injection?

[J-440]

I’ve seen fuel rail heat wrap but never a shield under the injection rail. How would that work?

[GregWeld]

Who programmed this EFI to begin with??? And are you sure you don't have a programming issue....OR a wiring issue to the pump (high resistance connection).... or perhaps the relay going south which then causes the pump to drop off.



The definition of insanity is to do the same thing over and over and expect a different result.

[J-440]

Hey Greg. I’m getting a 250 degree reading on about 2 feet of sending line that’s running right near my motor plate. The header is behind the plate. The plate and line are hot to the touch obviously. Gonna wrap this line with some better heat wrap and see what this does. Previous wrap didn’t cut it I guess. If this doesn’t work I’ve got some header heat shielding.