Does this sound like vapor lock?

[redhorseshoe]

Awhile back I posted about my 73 not getting any fuel to the carb. I got lots of helpful advice on here but, as it turns out, it was just the fuel pump. Long story short here's what's happening now. . . I changed the fuel pump yesterday, turned the key and she fired right up, idled great, no issues whatsoever. Drove around the neighborhood for about 40 minutes at low (20-35mph) speeds. Then thought I'd take it out on the highway. Pulled up to the stop sign and it dies. Kind of sputters a bit but then just dies. Fires right back up and I make it about 1/4 mile down the road and it does same thing again. Let it sit about 10-15 minutes and it starts right back up. Make it about 1 mile down the road and again, it dies. Finally, I have my wife come meet me with the pickup and we tow it home. In the driveway I start it and let it idle for around 20-30 minutes. Idle is smooth and everything sounds great. No leaks but did find the hard plastic fuel line a little close to the exhaust manifold so I moved it well out of the way.
Does this sound like vapor lock or is there something else it could be? No problems like this before fuel pump replacement and all I messed with when I swapped the pump was the fuel line.

Thank You for any Help!

 

[Broncomt]

Plastic or rubber fuel lines absorb and hold heat more than steel lines. I had same problem on my 68 stang 302. Changed rubber line from fuel pump to carb with factory steel line and solved problem for me.

 

[savage]

Do you have points or electronic ignition? Mine was acting like it had a vapor lock, and it ended up being the electronic box going bad.

 

[smokinjoe]

Does sound like vapor lock to me, except for it firing right back up that one time. But needing to sit for a few while the gas returns to liquid in the lines sure does sound like the Lock's MO.

Outta curiosity, what kind of ignition do you run? Coil & dizzy? How old is your gas tank outta curiosity as well? Do you use plastic see-through fuel filters, nice and clean?

 

[redhorseshoe]

Everything is bone stock. As in most likely all original from the factory, not just oem replacement. It is well taken care of though. New fuel filters, freshly rebuilt carb, etc. I just assumed vapor lock because everything was in good shape until after the new pump and all I messed with were the fuel lines.

 

[savage]

Pictures would help to see what you have under the hood. What did you do with the fuel lines? You posted you messed with them.

 

[half cab]

Coil could be goin bad? Trash in fuel line?

 

[redhorseshoe]

Sorry, "messed with" was a bad word choice. I removed and inspected the line from the tank selector valve to the pump then reinstalled it. I was just checking to make sure it wasn't damaged.

 

[FordBronc]

What about your carb housing fuel filter condition? Any inline fuel filters? Filter sock on the end of your pick up tube on the sending unit? Fuel tank condition?

 

[patterdale]

Bad pump out of the box? Pump drive eccentric spinning on shaft?

 

[Rustytruck]

Idle speed at 700 RPM?
When it dies pop the air cleaner and look down the carb with the engine off. Manually work the throttle linkage while looking down the carb and see if the accelerator works and the carb squirts fuel down in the carb. No fuel no squirt.

Might check the fuel cap vent. Remove cap and on the underside of the cap you will see a nipple with a hole in it. suck on the nipple. You should have air flow. Blow in it it should not blow out but no big deal if it does as a 73 has a vented cap. Air must come in the vent so fuel can flow out by the pump. No vent the pump pumps fuel until the vacuum in the tank wont let the pump suck fuel.

Don't want to do this test temporary drive the truck with the cap off. This is risky as you can slosh the fuel out the fill in a turn and spill gas where it isn't supposed to be. Can damage paint and or start a fire so if you do this your on your own. You have been warned the risk is yours.

Check the fuel lines from the tank to the carb any loose hose clamps or cracked lines can suck air. Easier to suck air than fuel especially at idle when the pump is running slow. If you have fuel squirt when stalled I would look to the ignition.

I would also check the ignition points gap and make sure they are not too close together. I would also consider changing the capacitor they fail like this when they get hot.

I would also chase all vacuum lines attached to the engine or carb and make sure they are not loose or cracked.

If you still have EGR on this engine, if it gets stuck the truck wont want to idle due to an exhaust leak to the intake manifold.

 

[RODRIG3911]

I had the same issue recently. For me it ended up being my fuel filter had something rattling in it that would eventually get sucked up to the outlet starving my bronco of fuel. It always started right up just like your and would die after it happened again. I switch the fuel filter and it runs like a champ now...... Just something else to check

 

[rwill]

Tank has a screen in it, they rust and or become clogged over time.Have you checked this?

 

[tortoiseracer]

Could you have cracked the main fuel line when messing around with them. Had this problem in mine. Has a hairline crack in the fuel line. Would idle fine but would not get enough fuel at higher speeds as it could not replenish the carb. This is assuming you are sucking fuel and not pushing it of course.
Chris

 

[RedLeg0811]

I had something like this happen and it turned out I needed to replace the vented cap. I have not had the problem since.

 

[blubuckaroo]

redhorseshoe, could you give a description of your car's power train, exhaust, and fuel system?
These things can affect vapor lock a lot.

 

[Show Links]

Coil could be goin bad? Trash in fuel line?

X2. Maybe the tank pick up screen gets clogged periodically as stuff floats around. Then again, maybe it's something else.

 

[redhorseshoe]

UPDATE: First off, thanks for all the helpful ideas. Lots of good info there. Here's what I've found out so far. . . I rechecked all my fuel lines and they are all in good shape. Brand new inline fuel filter. That being said, the problem is not fuel delivery. I started it in the driveway today and it would only idle for 2 - 3 minutes then die. After the second or third time I pulled the air cleaner off and manually worked the throttle and it is getting gas. So now I'm assuming it has to be an electrical issue? As I said earlier, everything is bone stock and most likely even original to the vehicle from the factory. Any ideas on what to check next?

 

[67RT]

UPDATE: First off, thanks for all the helpful ideas. Lots of good info there. Here's what I've found out so far. . . I rechecked all my fuel lines and they are all in good shape. Brand new inline fuel filter. That being said, the problem is not fuel delivery. I started it in the driveway today and it would only idle for 2 - 3 minutes then die. After the second or third time I pulled the air cleaner off and manually worked the throttle and it is getting gas. So now I'm assuming it has to be an electrical issue? As I said earlier, everything is bone stock and most likely even original to the vehicle from the factory. Any ideas on what to check next?

Hi. That gas u are getting wgen pumping throttle is not your idle circuit. I had a recent thread and had same finding with bad idle. My fix was pulling top of carb and idle screws and blowing carb cleaner down idle vent holes until ran free out idle screw holes. Also sucked all gas out of bowl to ensure cleanliness. Carb was only six months old and carb filter was three months. Xhad previosly cleaned main tank but not aux tank.

I added an inline stock metal old style mopar filter right after pump and so far so good.
After your carb rebuild what waz status of your tanks? Original? Trash gets past the little motorcraft filter easily apparently.