Vapor Lock?

[izzy_Britton]

So my truck is acting funny. at first i thought it was the fuel pump, or maybe the tank valve under the cab or maybe even the aftermarket hei distributor. but i am thinking it is likely a vapor lock condition? i have never dealt with a vapor lock condition before so i dunno what is it like.

This happened the first time about 3 weeks ago. I went camping, pulled my 16 foot travel trailer over the hills to the coast. on the way home cruising at 50(ish) mph the truck seemed to just run out of gas. Those of you with dual tanks know, when you run out on tank 1 and the truck starts to blubber, reach over hit the switch and a few seconds later your off an running again. this is exactly what it seemed like to me. I changed tanks even though i just left the gas station about 40 miles earlier... switched tanks, and it never would pick up and take off, finally it just died. sat on the side of the road for a while fired up the truck and off i went.

40 miles later it happened again. exact same way, but it wouldnt start at all, finally called for a tow truck and he hauled me the 65 miles home. once home the truck started just fine. disconnected the trailer and been driving fine ever since.

fast forward 3 weeks, to today. driving up the freeway, towing my boat, runs out of fuel in tank 1, switch to tank 2, off we go, 5 minutes later, tank 2 is out of fuel, stab it into a fuel stop and put 20$ in it and again off i go. I make it about 1/2 mile down the road to the freeway on ramp and it starts blubbering when i get on it to merge with traffic leaving me hanging and a prime target for a big rig. i need to drive 20 miles north and then 30 miles south to home again, and the truck blubbers the whole way exactly like it does when it is out of gas and you need to change tanks.

WTF!?

it seems to only do this under a load, when towing for example, and both today and 3 weeks ago it was over 100F. is it the opinion of ye readers that this could be a vapor lock issue? how do i fix it?

86 chev edelbrock 1406 carb, napa HEI (mallory clone) distributor, all emissions removed, 700R4 in low gear when towing never over 50 today or last week except when coasting down a hill. today was flat land with only slight rise and fall in elevation, noting horrible. temp reads between 200-210.

IDEAS PLEASE? i want to go to the lake next weekend but have nothing to tow my boat to the lake with.... GRR

[INSIDIOUS '86]

My ideas.

1. Coil can be going bad. Had this happen to me and I was up and down all over the truck trying to figure it out

2. Loose diverter valve connection/bad diverter valve

3. Gas cap is not venting correctly causing a lot if vacuum in the tanks. When it does this next pull off the gas cap and see if you hear any whooshing noises

4. Edelbrock carbs are known to percolate fuel when things get hot. A hot summer day can send it over the edge and cause fuel to bubble and boil raising the floats and starving it of gas and then vapor locking it. Phenolic spacer or heat shield or spacer/shield combo can fight this.

[75gmc454]

I have the same problem on one of my trucks. It will run fine for about 20 minutes and then it will run out of gas. Come back after it cools off and it will run fine again for about 20 minutes. So I put one of those clear filters in line temporarily. The filter will be empty when the truck stops. When you come back when it cools off, the filter will be full again on its own without the engine running.

The previous owner put dual exhausts on it. The pipe on the passenger side runs right by the gas lines and the selector switch, which in turn causes the problem.

Trucks with factory dual tanks AND dual exhaust (400 engines, 454 engines, and 350's with duals) have heat shields that protect the lines and selector switch, but many times they have been removed over the years.

[rich weyand]

x2 on the heat shields for the gas lines, particularly in the close area. Just look, you'll see what I mean.

also x2 on the spacer for the 1406. The Eddies are heat sensitive. You need a spacer between the carb and the intake manifold. I would get a wood one rather than a phenolic one for better heat isolation.
http://www.jegs.com/i/Edelbrock/350/8724/10002/-1

Finally, what are you running for air cleaner, open-element or stock? Are you running a cold-air induction setup through the radiator bulkhead between the radiator and the battery, or are you pulling air from under the hood? Best setup is the stock thermostatic air cleaner, and a cold-air induction tube from the snorkel to the radiator bulkhead.

[78trk]

I pull a 25 ft. trailer and have vapor lock problems when it gets around 100.
I insulated gas lines and it didn't make a difference this time. Changed the fuel pump and it pulls good for now.

[ETKTRYD]

Ethanol blend gas today boils at a lower temp than the old stuff.

[ETKTRYD]

Fuel return line ?

[motornut]

Originally Posted by ETKTRYD

Fuel return line ?

I wondered if you had two or three line pump?

[mrolds88]

One other thing that was not mentioned was to change your thermostat. I would al least use a 180* if not a 160. The lower it opens, the more room (temperature ) you have to work with. It drives me up the wall to see my stuff get to the temps you talk about on your truck.

[izzy_Britton]

Originally Posted by mrolds88

One other thing that was not mentioned was to change your thermostat. I would al least use a 180* if not a 160. The lower it opens, the more room (temperature ) you have to work with. It drives me up the wall to see my stuff get to the temps you talk about on your truck.

You posted this while i was typing up the previous post...

NO Thermostat is installed.

[izzy_Britton]

for discussion sake, and for completeness.

I am running a single exhaust that is routed same as the factory exhaust was routed. the exhaust changes to a 3 inch pipe at the point where the two pipes join. I have a flow master 60 series muffler that is mounted just rear of the stock location, about where the cat used to be located on the left side of the truck. the stock heat shields remain in place. I never even considered this a possible problem until it was mentioned. I will have to get the truck up on the lift this week to take a peek.

The tank switch valve might be too close to the exhaust, but i seem to remember there was plenty of room to access it without the exhaust being an issue, but once again i will take a peek when i get it on the lift. maybe i should bypass the valve for a while to see if this makes a bit of difference?

I have been running some sort of aftermarket air cleaner, a one piece, wire mesh thing that does not have a changeable element. when the truck started acting up i yanked it, and so for the time being no air cleaner is installed. yes i know how bad this can be, but in all honesty i drive 2 miles to work and home so including yesterdays trip i might have 100 miles on the clock since 3 weeks ago.

I have a chevy to square bore adapter? under the eddy now, is it safe to put the wooden/Phenolic spacer between the adapter and the eddy? only one spacer or should i put 2?

so last night after typing up the original post i went out and popped the hood, the see thru filter was indeed empty, took a few minutes to get it to normal fuel level and ran like crap the whole time, until filter filled.

The fuel pump in the original pump, perhaps i should change it just for the sake of preventative maintenance? typically a fuel pump wouldnt work KINDA some times, usually the work or they dont, for this reason i decided the pump was not the problem, but who knows. I just hate knowing that the fuel lines will be stuck to the pump and i will have more fuel line issues just for changing the pump. wachu think?

I think i will see if napa has a new coil in stock.

I dont really want to go about changing a whole bunch of stuff at once and never know which was the problem if the problem gets fixed, know what i mean? but i also dont want to be working on this thing constantly until i figure out what the problem is either, only to toss it all out and throw the LS1 in, which will undo everything we are discussing now. but that is not will late this year early next year.

did i forget anything?

i owe, i owe so off to work i go, i owe, i owe.

[ETKTRYD]

Check with your local Marina... Marina's do not have to sell Ethanal. Fill some jugs and try it in the truck.

[rich weyand]

You can put the spacer between the 1406 and the adapter. Rather than use two, you can get a 1" thick one instead of the 1/2" thick one. You will need to make sure you have carb studs long enough to span the carb base, the spacer, the adapter, and still get you deep enough engagement into the manifold.

Sucking hot underhood air into the carb when the engine is loaded hard does not help. Getting an air intake from in front of the radiator would help.

That being said, the filter being empty means the problem is likely upstream of that point; that is, toward the tank. Original fuel pump means it's 30+ years old, so I would replace that on general principles.

Also, check for clearances between the fuel line and the exhaust all the way back, beginning at the fuel pump. The issue with the exhaust is radiative heating: infrared radiation (i.e. light) from the hot exhaust heats everything around it, just like the element in a toaster. A heat shield only has to be substantial enough to 1) stay in place and 2) block the infrared light. A couple pieces of sheet metal may be all you need to fix the problem.

[donut]

I was thinking along the lines as Dead Parrot. Rotted feed line sucking air or a venting issue. Fuel line just have to get dirty and inspect. Vent issue, try cracking open the gas cap. Not real glamorous, but cheap to check and eliminate.

[86c20]

this is word for word what my c20 just did. start fine run fine till a good load at first..... then it was empty wot then it was at 60 then 45 then 30 then no start then just run then complete crap and would almost not move. change the fuel pump. better yet get a cheap elc one. the stock was 22 bucks at my napa. i have had my truck 8+ years use to pull alot of heavy trails all summer long and never had a vaper lock ever. and i would go all day 90+ heat and never shut her down. thats stock qjet. the wreaker i have has a edi and i had 2 problems after running the pto that is right next to the starteer and fuel lines. one stalled crank no start the other no crank at all. only thing i did was a spacer that my dad had that is like the air cooled motors and has fins. never another problem

[izzy_Britton]

well it is getting worse... wouldn't hardly run me the 2 miles to work this morning. noload, other than truckitself, 71F.

fuel pump in hand, replacing that tonight, and whatever rubber lines I can get my hands on to replace. mightp put a fuel filter on the frame somewhere while I am at it if easy enough to do.

gah! if it ain't one thing it's another.... always!

[rich weyand]

Getting worse is interesting.

Check your timing. My distributor was not clamped down tight, and it got more and more retarded, and had less and less power.

[izzy_Britton]

Just an update:

installed new fuel pump and replaced rubber fuel lines between frame and pump, and pump and carb.

since I had it apart, I also replaced let radiator hose.

the thermostat thatI previously said was not installed turned me into a liar. I removed the thermostat last night. I now have 2 miles on the clock, will drive it further tomorrow to see if it was indeed the fuel pump. seems better in that 2 miles, but it has been an intermittent problem so time will tell.

[shippman]

Watching this thread very closely... I have the same problem. I have an '82 with '91 throttle body injection, dual tanks. So far I have experienced all of the same symptoms as posted. I have replaced fuel pump (external electric), fuel filter, and the short rubber tubing at the selector switch. Symptoms still occurring. The last time it happened, I opened the gas caps a little and that got me home. The charcoal canister was removed some time ago and I use the tube going back to the tanks for my return fuel line from the TBI. Still looking for answers... any more suggestions?

Frustrated in Texas

[hatzie]

I've had a couple mechanical pumps intermittently fail.
I also had a tiny pinprick burn through in a rotor do the intermittent shutdown bit. Wouldn't have believed either one...

[izzy_Britton]

pulled the boat this past weekend, its too early to say, but i think the fuel pump replacement has solved the problem... for now, seems to early to tell for sure. I will be pulling the boat again this coming weekend, will report back if anything does or doesnt arise.