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fuel delivery probs, advice appreciated

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 82TOYLB, Jan 13, 2002.

  1. 82TOYLB

    82TOYLB Registered Member

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    This might be lengthy so be patient. I have a '79 K5 with a mildly built 350 (crane cam, edelbrock intake) that was just rebuilt to stock specs by a ruputable engine builder in Sacramento. It is running the stock q-jet that has also just been rebuilt. It runs just fine 99% of the time. Shortly after installing the motor I wheeled the Rubicon in june in 80 degree weather with no problems, and initial starts were easy with just a few cranks. My first problem was later last summer I was driving through Santa Rosa on a 104 degree day and when I stopped at a grocery store it started fine and then just idled down and died after running about 6-10 seconds. I could not restart the truck until I had someone spray starting fluid down the carb and spin the motor fast for a while to re- prime my fuel pump/lines. I had no further probs until in august I went to wheel the fordyce and had it seem to vapor lock on me 4-5 times in a couple of hours. If I turn it off it will start easily then die after 6-10 seconds and then not start unless I let it sit for 15-20 minutes, them it starts fine after a little cranking. In between the Santa Rosa incident and the fordyce it ran and started beautifully the rest of the summer in Sacramento. Another problem that I think might be related is that when I park it for the night now it seems to lose all its prime, the fuel runs all the way back into the tank and I have to crank it for like 15 seconds to refill the pump and bowels in the carb befor it will start. Another interesting thing is that I have had the most trouble out on the trail were I am just crawling, kind of like without enough airflow down the framerails the fuel lines are getting too hot and the fuel is vaporizing. This theory is ok until yesterday I went snow wheeling and it was probably 40 degrees outside and I was just wheeling up a snowy road, I was pushing some snow but did not appear to be working the motor that hard. The truck seemed to vapor lock again. This time I just put it in park and left it idling. Got out to take a leak and it idled down and died after about 20 seconds of idling and would not restart. After going for a quick hike and throwing some snowballs with friends for about 30 minutes it started fine after 10 seconds of cranking. The truck has a brand new modine radiator(new with engine rebuild about 10 mo\5,000 miles ago), water pump and hoses, thermostat, and never runs hot or even warm in the summer. (Temp gauge works well) The fuel system has no leaks in it, no damp spots on any of the lines, no smell of gas at all and I have a sensitive nose. It does run duel exhast and an exhaust pipe runs down the Right framerail where the fuel lines run, but it is still 6-12 inches away from the fuel lines and especially in cold weather would doubt the lines get all that hot, I have felt them and they don't burn my hans at all. Can a fuel pump (also new) malfunction in this way by losing prime when you let the truck sit longer then about 10 hours or by vapor locking even when cool. How about a canister or what? I have thought about sleeving all of the fuel lines with a heat sheild like jegs or summit sells for that but thought I would get some advice before shelling out the money. Prior to the engine rebuild the truck ran the duel exhaust for about five years in the same place with no vaporlocking events. I also ran new rubber fuel hose at all the tank attachments and at the fuel pump at the time of the engine/tranny rebuild. New fuel filters also. Any thoughts would be appreciated before I throw the carb away and get a tbi setup. Also would an inline electric fuel pump be of any benefit?
    Thanks.
    Michael.

    82 Toy LB with Marlin, locked, 36's,38's,35's depending on month/mood. 79 K5 with 3/4 ton running gear, 36's.
     
  2. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    It almost sounds like the diaphragm in your fuel pump has gone bad or developed a crack in it.

    FWIW, I run an aftermarket Carter electric fuel pump on my 84. I had some similar vapor lock issues with my 305, and I found out from a buddy that his 305 had done the same thing because the cam lobe that powers the mech. pump was worn. I installed the electric pump almost 8 years ago and haven't had a fuel delivery problem since.

    Also, you may have recieved a bum fuel pump when you did the rebuild. God knows how many times I've had to replace "new" parts within a week or two because they the manufacturer screwed up.

    One other hint: Chevy parts reall prefer to be installed on Chev vehicles. I bet if you ditched the Toy your problems would disappear!!!![​IMG] j/k



    <font color=red>DIGGING AND DIGGING AND DIGGING</font color=red>
     
  3. 82TOYLB

    82TOYLB Registered Member

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    Thanks canmorek5. 24 looks and no one has any more wisdom. Come on guys, someone has got to have seen something like this and have some advice.

    82 Toy LB with Marlin, locked, 36's,38's,35's depending on month/mood. 79 K5 with 3/4 ton running gear, 36's.
     
  4. AGM73k5

    AGM73k5 1/2 ton status

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    <blockquote><font class="small">In reply to:</font><hr>


    no one has any more wisdom


    <hr></blockquote>
    Sorry guy, there are always alot of lookers on posts. If you don't get any more good responses you might try the search feature. I wish I had something to add but Paul (Canmore) covered everything I could come up with.
    Good luck,

    -Aaron

    ___ __ _ _ ____ __
    AGM73k5 -- ajgm1@yahoo.com
     
  5. TJS

    TJS 1/2 ton status

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    when you had your motor rebuilt did the builder use the fuel pump pushrod that came out of it or did he replace it. I have seen these wear a little that may or may not cause the problem. A bad pump can also be this cause as well. Hope this helps some.
    T.J.
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    Could be push rod for the fuel pump, but I'd be more inclined to say not likely. if it was the fuel pump push rod, why only when its hot? Why not always? Engine doesn't demand any more fuel whether its been driven 5 miles or 50. (choke off of course)

    You say vapor lock, I say doubtful here as well, unless modifications have been made to the fuel or exhaust system, routing the fuel lines too close to the exhaust, vaporizing the fuel BEFORE it gets to the pump. Ever checked for fuel after the pump when its acting up?

    How about a pressure regulator? have one installed? Seen one act like vapor lock when it was failing. Only when hot, wouldn't restart until it cooled off. Also fuel tank filter. I don't know what a "safe" temp is for the carb, perhaps engine is running too hot, and the fuel in the carb is boiling when fuel demand, and overall cooling, is least. How about float level? Incorrect float level might allow the carb to heat up the fuel if too little is in there at all times.

    First thing I'd check is if you are getting fuel to the carb when its "acting up". Either check for accelerator pump shot or fuel being pushed by the fuel pump with line to carb disconnected, obviously will needc an assistant. Be careful, I figure you don't need an engine fire.

    Dorian
    My tech/links page: <a target="_blank" href=http://www.dorianyeager.com/index2.html>www.dorianyeager.com/index2.html</a>
    Why insist on counting when the ring gear has the tooth counts stamped in?
     
  7. 82TOYLB

    82TOYLB Registered Member

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    Thanks for your replies. I am thinking that it is probably that my carb is getting too hot, with the aluminum intake and that the float level may be too low. Some input from folks on the pirate board led me to believe this might be the case. Will try to fix a few probs. ie. New fuel pump, sheild fuel lines, raise carb 1/2 inch on heat dissapating spacer, and raise float level. With all this done I think I should fix the problem. Don't know when I'll get around to it, but will post back when I do to let ya'll know if it accomplished the end goal.
    Thanks for your input.
    Michael.

    82 Toy LB with Marlin, locked, 36's,38's,35's depending on month/mood. 79 K5 with 3/4 ton running gear, 36's.
     
  8. chevy/cj

    chevy/cj Registered Member

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    did you install any rubber line on the tank side of the pump? It might be collapsing. new motor new carb new pump= more fuel demand+cheap fuel line=flat line. I could be wrong but its a guess.

    It was a jeep thing but that stuff broke!!
     

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