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Vaopr Lock and SUmmer Heat

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by spencerjw, Jun 27, 2002.

  1. spencerjw

    spencerjw Registered Member

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    Well, I am about 99.99% certain that Vapor Lock is the problem here.

    I live in Arvada (for those of you form CO) and I commute to the tech center everyday. Mornings are great, nice and cool, evenings around 4-5pm suck because of the heat and traffic. I can usually get to about Highway 36 before I have any problems, sometime farther. However, after a while my truck starts to shudder like I'm running out of gas, eventually it just stalls all together. This usually is noticible when I have to give it gas for a hill or something. It's happened twice now and only a rest of 3-4 hours will cure it.

    My question is, what are the solutions for vapor lock? I heard about the cloths pin deal but that did *not* work, unless I have them in the wrong spot.

    I have an 1986 K5 Silverado, 305 V8. If anyone could tell me where I'm supposed to put them that'd be great. Right now I have them on the metal (silver) line that looks to be about 6-8 inches long and runs from below a pump and the air filter intake. This didn;t seam to help at all last ngiht on my way home. I have about 5 or 6 pins on there.

    What else can be done? Relocating the line I hear about also, but is that easily done? It doesn't seam to be since I can barely tell where the ends of the line are, muchless be able to access them easily to move them.

    Any assistance you can provide would be greatly appreciated!!!
     
  2. BlazerGuy

    BlazerGuy 3/4 ton status

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    When was the last time you did a complete tune-up on it?? It may be a screwed up choke, clogged up fuel filter etc. Is the 305 running at a normal temp??? Are you running custom dual exhaust? When I installed my dual exhaust the passenger side pipe was too close to the fuel lines and caused vapor lock so I had to rig up some heat shields for it and it runs fine now.....
     
  3. spencerjw

    spencerjw Registered Member

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    I've only owned the truck for 6 months and I'm now selling it ($ issues and drive times). So no, I have not done a tune-up myself, not sure if the prior owner had or not. It's only got 108,000 on it and it's basically completely stock. The engine runs at a great temp, no problems there.
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    Unless something has been changed from stock, its not vapor lock. This is a problem that in actuality rarely occurs unless the exhaust has been routed too close to the fuel lines, and that would not be the case with a stock setup. The trucks didn't vapor lock when new, they won't magically vapor lock later. They were built to go to any of the 50 states (minus CA lol) and since the fuel system is the same for all of them (pump, line routing, etc) vapor lock is not an issue.

    How about things like a faulty fuel pressure regulator if added, a bad "sock" filter in the tank, crud in the tank, bad fuel filter, bad float, etc.?

    My car (when its running) gets up to 220*, and although not right, it does not vapor lock. Only 108 cubic inches larger than the setup was designed for.
     
  5. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    Actually, Dorian, I have to disagree(sorry /forums/images/icons/wink.gif ). 305s are notorious for premature wear on the cam lobe that powers the mechanical pump. This causes the pump to run less fuel through the lines to the carb which in turn allows more heat soak than the system can take.

    I spent 16 months trying to resolve my fuel issues(which sound very similar to those above) and the only way I resolved it was to eliminate the mech. fuel pump and go to an electric, which has worked trouble free for over 8 years.

    I have heard this story over and over again from 305 owners, BTW.....
     
  6. 19Jimmy87

    19Jimmy87 Registered Member

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    This is exactly what is wrong with my truck. I have an 87 TBI. What exactly do I need to get checked? This is very frustrating driving in Detroit in rush hour. Every time I decelerated, stalled. This issue alone, if can;t be fixed, prompts me to want to sell. You know what else that might help you figure this out for me...I found a little clear fluid under the air intake cylinder. It is too hot to touch.
     
  7. Pure Insanity

    Pure Insanity 1/2 ton status

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    Look for any places that the metal line gets close to the block. My exGF dad bent up a new line for me once and it got too close to the block and I had vapor lock bad.

    Clothes pins dont work BTW.

    An electric pump will most likely eliminate VL also. A mech pump works from a diaphragm that "flutters" and compresses the air, (the fuel pulsates as it comes out), then it just expands back. An electric pump doesnt pulsate, so it doesnt compress air and expand. It compresses it and shoves it through. /forums/images/icons/grin.gif
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    Hey just because you've seen something I haven't, doesn't mean it can't happen! : )

    To tell you the truth, this is the ONLY place I've heard people complain about 305 cam lobes failing on. I'm not implying anything, but I know more than a few people running 100K plus mile 305's that haven't had this problem, myself included. (when I had a 130k 305).

    Of course, I did have the fuel pump fail, but thats a different story!

    If the fuel pump is faulty, in my thinking, the harder you try and run it, the worse it will get...you'll run out of fuel. It's not that hard to do with a Q-jet if you try or are having problems. You're problem could easily have been that the engine wasn't getting enough fuel due to the amount being pumped to the carb, not that it was moving too slow.

    But obviously, if the cam lobe is shot or the pump is weak, you can have a myriad of different results. I'm not quite sure how you could check this, except perhaps crank it with the fuel line off the carb, and see what kind of volume its pushing, or get a fuel pressure gauge...
     
  9. trailblazer87

    trailblazer87 1/2 ton status

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    Mine did this due to a couple of different reasons. Check your fuel pressure regulator, it might be old and not working right, its right behind the injectors, and is an easy fix. When I replaced mine I got all of my power back that I never even knew I had lost. The other cause could be a clogged fuel filter or a dying fuel pump, the tbi runs at about 60 psi, if you are not getting that then your injector spray pattern will not be very good.
     
  10. littledonnieb

    littledonnieb Registered Member

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    Been there...doing that. try locating your electronic (I assume) as close to your gas tank as possible.
     
  11. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    The problem was definitely not a bad pump. I went through 4 fuel pumps in 16 months- after about 3 or 4 months of use the vapor lock would happen again(I even tried a pump straight from GM just in case). It was almost as if the new pump diaphragm was stiff enough to send enough fuel through and overcome the heat soak, but after a few months in service the diaphragm would weaken and wasn't able to produce the volume needed. The only wasy to get the truck started after a vapor lock was to let the engine cool off and prime the carb with raw gas.
     

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