Vapor lock?

[mobileortho]

I've been trying to figure out why the truck has been running so irradically and someone suggested that it may be vapor lock. It runs fine when I initially start it but as soon as it heats up I notice that there's no fuel coming through the filter and it barely runs. The fuel pump is brand new so I ruled that out. I'm looking into an electric unit with a low pressure switch to see if that will help. Any other suggestions?

[T Hilde]

Was the tank cleaned? Just wondering if something is trying to block the pick up point.

[mobileortho]

Yep.

[GeorgeVale]

where do your fuel lines run? I have seen lots of fuel vaporisation problems where they run next to or close to exhausts and across exhaust header.

[OrrieG]

Stock or V8? You need to get it heated up then check the line into the fuel pump. Just because its new do not assume its good when it gets hot. Doesn't happen often but a slight defect in the diaphram can show up when it gets hot or at higher rpm. Did you replace the lines when you had the tank cleaned? I had a rig once that got some cruddy gas; I dropped the tank and cleaned it, flushed the lines as best I could and still ended up replacing the line. Also, if you have a glass or plastic see thru fuel filter I'd think about replacing it with a metal cannister or screw on type. If everything checks out look at rerouting the fuel lines and using header wrap to insulate them.

[Atomsplitter]

Your running a TPI right?
Is you fuel pressure regulator working corrrectly?
Maybe the return line is blocked?
Is the tank venting properly?

[OrrieG]

If its TPI ignore my post, pump is in the tank on those right? If its a closed system and not set up right will the tank build up vacuum and not pump, like turning a water bottle up side down?

[mobileortho]

I switched to a carb earlier this year.

[mobileortho]

My brother-in-law told me to check the lines as it might be sucking air from some place. I forgot to mention that I'm getting some strange readings from the fuel pressure guage. Sometimes the needle bounces around wildly and then at times it holds steady at about 5-6 psi. Any thoughts?

[mr48chev]

You might carry a cooler of ice water along and if it does act up pour some on the fuel pump and line and see if that gives it a temporary fix.

Way back when I had a 283 in the 48 I had to do that one time on a very hot day while pulling a hill in Utah.

Other things to check are the the sucking air that your brother mentioned and how is the tank vented?
Have you made any changes to the fuel system lately like changing the gas cap or rerouting a line?

[63 & 64 Bowties]

An "old-timer" remedy for vapor lock that DOES work:
Take some wooden clothes pins and put them on your fuel line between the pump and carb. Five or six if you have the room. They will dissipate the heat and solve your problem. At least this way you'll know if vapor lock is the problem.

[mobileortho]

I replaced the mechanical pump with an electrical one and most of the rubber lines with steel ones. Started and ran fine, Pressure guage held rock steady @ 5 psi. headed out for a test drive and it did the same thing...ran like @($%@&! & on top of that the brakes started locking up agsin!. The only other alternative is to check the carb. I'll see if one of my buds will let me borrow one just to test this theory. I'm getting pretty tired of this!!!!!!!

[av8tr33337]

One question. You say your breaks started locking up. Some chevy break boosters use vacuum assist if yours does and you are having probelms with the way the engine runs, could it be a simple vacuum leak?? Possibly something that only leaks after the motor heats up??? just a thought. I could be way off.

[Atomsplitter]

Just a shot in the dark but...

Is the block from an LT1 with reverse flow cooling?
They had issues with heat build up at the rear of the cylinders that cause the premature failure of the intake manifold gasket at the back corners. There was a small port that had to be vented through the throttle body, which heated the throttle body for winter driving, and the flow path continued to the radiator. Many people remove this steel vent line to keep the throttle body cooler for more Horse Power.
Check that the intake manifold at the rear of the motor is sealed properly.

[mobileortho]

I'm outta ideas. I swapped the carb and it's still running lousy.

[CAL 58 GMC]

I had the same problem. My truck would run fine until is got heated up and the would run extremely lean and would die. I did all of the checks, fuel line, fuel pump and filters. I ended up installing a high-pressure electric fuel pump with a fuel regulator. I'm now running around 8lbs to 9lbs. pressure. The problem went away.

[gdiwicker]

Originally Posted by CAL 58 GMC

I had the same problem. My truck would run fine until is got heated up and the would run extremely lean and would die. I did all of the checks, fuel line, fuel pump and filters. I ended up installing a high-pressure electric fuel pump with a fuel regulator. I'm now running around 8lbs to 9lbs. pressure. The problem went away.

I'm having this problem too. The 350 in my 67 c10 is from an 87 suburban. I'm going to try the clothespins for a temp solution but I think the electric would be the way to go. Can you give the details about your setup?

[_Ogre]

have you tried running with out the gas cap? tank vented?

[dwcsr]

I'm thinking its a tank issue. Either something blocking the pickup of not vented enough or a hole in the tube above the gas level.

[gdiwicker]

I haven't run it with the cap off. I'll do that.

I think after trying to drive today (eighties, cool, and wet), and the engine wasn't nearly as hot as when it failed the other day, that the first thing to do is the change the filter. I can see some junk in the filter and its easy to do. I'm thinking the clog attributed to diminished fuel pressure thus making a better environment for vapor lock to occur.

[dwcsr]

Originally Posted by gdiwicker

I haven't run it with the cap off. I'll do that.

I think after trying to drive today (eighties, cool, and wet), and the engine wasn't nearly as hot as when it failed the other day, that the first thing to do is the change the filter. I can see some junk in the filter and its easy to do. I'm thinking the clog attributed to diminished fuel pressure thus making a better environment for vapor lock to occur.

On your truck if you have a 3 line pump plug the return line back to the tank. My 72 did the same thing until i plugged that line.

You probably should start your own thread so we don't get confused as to whose truck we are diagnosing seeing as you have different fuel systems.

[mr48chev]

I don't see vapor lock as the issue if you have an electric pump at the tank. From experience it happens with a mechanical pump and fuel lines to the mechanical pump running too close to the exhaust.

That happened to me in Utah as I said earlier and my son and I got pretty good at pulling to the side of the road and throwing a cup of ice water on the fuel pump and another on on the intake and going again until it acted up again on that five mile or so grade that took us over an hour to make it to the top. That was with a 283 and small four barrel in the 48 though.

I'd look at the whole fuel system from gas cap to carb and try to figure out where the problem was.

Some issues might be:

Cap that isn't venting properly.

pickup tube clogged with some foreign object at times.

pickup tube in tank sucking air for some reason.

fuel line too small for the engine you have. If it's 5/16 coming out of the tank and turns to 3/8 it still works like a 5/16 line.

Kink or smashed spot in fuel line or hose.

Fuel line too close to the headers or exhaust pipe.

Vacuum leak created by carb install. That could be wrong gaskets, adapter plate or carb doesn't match intake.

Clogged fuel filters: the first thing I would do is change the fuel filters. If you have one of those cute take apart see through ones get rid of it and get a real filter before you burn the truck up. At some time those will leak. It isn't if but when.

If the Lt engine is getting hot did you swap belts and not swap water pumps? Serpentine belts use a reverse direction pump that won't work with V belts. They tend to cool the engine at an idle but it gets hot as soon as you get up to road speed. I ran into that years ago when someone stuck an earlier engine in a Camaro that came with serpentine belts that had V belts on the engine and then bought a water pump for the year model of the car rather than the year model of the engine. I don't believe the flow of the coolant is changed in the engine just the direction the blades in the pump work at. In other words the pump works counter clockwise rather than clockwise.