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Old 10-24-2006, 05:36 PM
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Need help with vapor locking

Well, this is the second time now that I"ve been stuck good due to vapor locking on my truck. I've had the problem off and on for a few years but it always just chuggs a bit after sitting idling but recovers once moving.

Today, I stopped at Jack in the box and waited a few minutes. PUt it in neurtal, A/C turned off. Pulled through, stopped in the lot to fix my burger, pulled onto the main street and it started jerking and finally quit all together. Was able to cost to the next side street and pull off. Ate my food, got out and poured some cold water on the fuel pump and it started back up and ran fine on the freeway at 70 all the way home. This is now the second time its stranded me with a full shut down.

Engine always runs cool, a solid 180 right now, even idling for extended periods.
This is the second pump, same problem.
Feed line from the tanks to the pump is re-run totally away from the engine and on the outside of the frame rails. Been like this for years.
Fan is turning good with stock 7 blade killer fan and good clutch.
Shroud is in place. (always has been)
Fuel lines have been in the same place from the pump to carb for the past 20 years. (metal line from pump to just before the carb, then rubber to carb.)

I've thought about wrapping the fuel pump and metal line with tin foil but that can be a two edged sword too. It can help insulate it, but will also keep it hot once it gets too hot.

All I can think about is the gas! Has anyone had problems with vapor locking with a particular brand of gasoline? I've been using QT brand here for about 2 years and it seems ok. Kinda at a loss on what the heck is causing it. All I know is I have to fix it somehow. Last time I almost needed a jump from cranking so long. Got lucky this time and it re-started after cooling it down. One of these days, it's going to strand me bigtime! Guess maybe I could re-route my wiper squirter so it sprayed on the pump? LOL

Any suggestions?

Mark

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Old 10-24-2006, 06:00 PM
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How old is the pump?

They do wear out too. And vapor lock is a sign of the diaphram inside getting weak.

It's not impossible to buy a new fuel pump that vapor locks.

You've done some good things by getting the fuel lines away from any heat source but the age of the pump could be working against you?
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Old 10-24-2006, 06:58 PM
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this pump is about 4 months old and came from a reputable shop.

I thought that vapor lock was when the gas got too hot and turned into a vapor in either the pump or line?
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Old 10-24-2006, 07:08 PM
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have you tried a heat shield under the carb? Or better yet if its an older SBC they had exhaust holes under the carb for {pre heat}could check for stuck heat riser in exhaust manifold putting heat through intake. Just some ideas. Easy enough to check with thermo temp probe. or hand held temp sensor. Good Luck
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Old 10-24-2006, 07:14 PM
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I have not tried the heat shield, although I did spot 2 of them in my tool box from years back. These are the same size as the carb base gasket and about 15 thousands thick.

I don't have a heat riser, got some cheap junk Hooker headers! LOL

I have the Edelbrock 2101 Performer with the exhaust crossover restricted but functioning. I"ve run that manifold for over 20 years with no carb percolation that i'm aware of. I always use the stock 1/4" thick fiber mounting gasket...seems that it would be a pretty good insulator.

I suppose I could 86 the mechanical pump and go electric back by the switching valve for my dual tanks, but was hoping not to resort to that. Not really fond of aftermarket electric pumps.

Maybe switching brands of gas might help, atleast thats been suggested in some articles I've read. Just hate to to that too cause QT is right at the end of my street and there are no brand names close by.
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Old 10-24-2006, 07:14 PM
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Vapor lock

Have you checked for a vacuum lock? If the tank is not vented properly it would mimic a vapor lock.....russ
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Old 10-24-2006, 07:17 PM
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Both tanks have vented caps. (77 chevy truck) It will run fine all day long on the highway but hates sitting still for 4 or 5 minutes.

Maybe tomorrow i'll do a pressure ck on the pump and see how its doing. You never know, it could be weak.
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Old 10-24-2006, 07:26 PM
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I had a 78 that would only run on one tank-
Changed the valve and fuel pump.
I was beginning to think that perhaps something was amiss in the sending unit.
????does this only happen on one tank, or both.????

(girlfriend's daughter tossed a rod in it before I dropped the tanks to inspect)

Perhaps it is sucking some air from the valve or tank fittings

Bryan

(when my 79 did it---was a pump)
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Old 10-24-2006, 07:34 PM
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vapor lock

Can you check the line and fuel pump area with a infrared thermometer, to see where the heat may be coming from?....russ
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Old 10-24-2006, 07:56 PM
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I drive a 77 with duel tanks also, my switch over valve went bad and I thought it was vapor lock also but looked under and found fuel dampness around valve. Also that valve sits real close to the exhaust pipe, just runing on now so I'll stop. Good luck.
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Old 10-24-2006, 08:46 PM
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I appreciate all the replies.

The switch over valve is new, well, last year anyway. If I was sucking air, I would expect some leakage when its off, but will crawl under it and take a look.

It doesn't seem to matter which tank its on.

I have a large metal Fram inline filter about a foot from the pump on the inlet side, about where the frame is. I also have the little paper insert factory Qjet filter in the carb. inlet. Maybe I'll also change the big metal filter to a big plastic one so I can see if it's going dry when this happens.

My son has an infered temp. gun that I can use to ck it over. It just seems so odd that it's been going on for so long and now has all of a sudden gotten worse to the point of shutting me down completely. Guess it's pump and filter time and a good ck over and see what happens then. Glad the pump is an easy 10 minute change! (no air pump on top of it!)

Mark
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Old 10-25-2006, 08:38 AM
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I had the same problem years ago when I was stationed out in Arizona with my Olds. The first time I actually vapor loked and would not restart ater sitting for a short time was out around Indian Springs as I left out of Vegas for Tahoe one summer. Man, that was a bad place to break down. That was the first time I went to an electric fuel pump and I put it in on the side of the road. It worked good for the rest of the trip, but I sure hated the "brrrrp" every few seconds as it pumped up, but I hated sitting on the side of the road in the middle of nowhere worse! So, every summer, I went back to the electric pump while I was there. Now, here in Florida, I don't have the problem. I hear the newer solid state pumps are dampened and aren't as bad. I don't know. May be something to consider.
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Old 10-25-2006, 11:50 AM
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Well, made a few changes. I got to thinking on the heat issue. I"ve cooled down the engine and radiator and the fan is pulling HARD at idle, especially in park. It idles at a grand in park due to the cam. I changed out the inline filter to a clear one just to see what's going on. It's before the pump but I got to thinking about the only thing thats NOT cooling down now that the weather is nice...the exhaust! I crawled under and the switching valve and hoses are about 5" from the right pipe just ahead of my Magnaflows. So, thinking that that could be the source of heat that is killing the flow when it sets, I made a sheetmetal shield to completely cover the valve and hoses. Thing is about 14" long and goes from the frame to the floor pan. Time to go for a hard drive on the freeway then pull off and let it idle for a while and see what happens. Sure hope this cures it! Just need to make sure i'm close to my sons shop when I pull over! LOL

Mark
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