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This sputtering problem is driving me CRAZY

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Lotsa_Faith, Aug 3, 2003.

  1. Lotsa_Faith

    Lotsa_Faith 1/2 ton status

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    Alright I THOUGHT my truck was running good and had somehow gotten rid of the sputtering/stalling/bogging problem. Not so as I found out last night at 1 in the morning. This is what happened. At about 6, I went and filled it up with gas. It was at about 1/8th of a tank, and was running GREAT, I could actually put it to the floor and it wouldn't sputter and hesitate. When I unscrew the gas cap, its always got a lot of pressure in the tank. After I filled it up, on the way to the ball field, it ran just as good. Then, at about 1 when I left the field, it was sputtering and bogging so bad that I could barely get it to 30 mph. What could be the problem?
     
  2. sapper

    sapper 1/2 ton status GMOTM Winner

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    mine was doing something similar, alot of backfiring, sputtering and then it just died, mine turned out to be the coil was bad, check your plugs, plug wires and cap&rotor and coil, its prolly one of them
     
  3. Lotsa_Faith

    Lotsa_Faith 1/2 ton status

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    but why would it only do it after i let the pressure out of the gas tank? its got new plugs and wires, and i know the wires arent switched or anything cause it runs fine 90% of the time, no missing...
     
  4. NightRider

    NightRider 1/2 ton status

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    hmm, well...i had that problem only when i gunned mine/petal to the metal, like when getting on the highway, it would just kinda cutt off for a hot second and then it'd be fine. come to find out, i had blown a spark plug gunning it and was only running with 7/8 cylinders. Be positive its not your spark plugs
     
  5. Lotsa_Faith

    Lotsa_Faith 1/2 ton status

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    i cant work on it right now, cause i recently had knee surgery so i'm on crutches. I still don't see why a plug would only go faulty after you let pressure out of the tank. I was thinking more of a weak fuel pump problem?
     
  6. RustBuket

    RustBuket 1/2 ton status

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    Yes, fuel pump could be it? Maybe its vapor locking?
     
  7. sapper

    sapper 1/2 ton status GMOTM Winner

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    for a few days i thought my problem was bad gas or water in the tank because it sat empty for the 6 months i was gone, somedays it would work somedays it sucked, after putting in dry gas a injector cleaner it ran great then [I love Jeeps] the bed agian, turned out to be the coil, after 14 years it died
     
  8. Mastiff

    Mastiff 1/2 ton status Premium Member

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    Sounds kinda like a plugged tank vent? Not sure though. I don't even know where the tank vent is, but if it's plugged you'd build up vacuum in the tank. Can you tell I'm making this up as I go? /forums/images/graemlins/tongue.gif Hoping maybe to trigger a thought in someone who actually knows something. /forums/images/graemlins/grin.gif

    Does it suck air in when you open the gas cap? Have you tried just pulling over and opening the gas cap when it's running bad to see if it gets better?
     
  9. Lotsa_Faith

    Lotsa_Faith 1/2 ton status

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    when I open up the cap, all i can smell is strong fumes. So its not making a vaccuum, its building pressure inside the tank, thats why i'm thinking its relying on that pressure to feed gas to the carb, and when i let the pressure out, it sputters and stalls.
     
  10. mike reeh

    mike reeh 1/2 ton status

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    It definately should not be building pressure. One of my tanks in my pickup used to do that.. it would build a LOT of pressure.. When I removed the gas cap it would almost knock me out with all the fumes.. Turns out the vent in the sending unit was somehow frozen shut or something. I ended up drilling it out. I have since replaced the sending units, but that fixed that problem. It should be vented at the sending unit then a line should run into the engine compartment to the charcoal canister.. That is probably not why your engine is running bad though. Did you check to make sure there is no clogged fuel filters or kinked lines or anything? if it revs no problem in neutral, but under a load it dies, it could be starving for fuel.. Could be a real weak ignition too, but the easiest to diagnose and fix is the fuel system. If you dont know the history on the fuel pump, just buy a delco one and replace it! good insurance. Even if it doesnt fix the problem, it fixed a future problem. Replace all the fuel filters while you're at it. A fuel pressure guage to install in-line befire the carburetor would be handy also. something with a long enough hose that you could read it while test-driving (set it on the cowl or whatever) Theres my 2 cents

    mike
     
  11. 83PJW

    83PJW 1/2 ton status

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    the whole getting gas thing might be a coincidence too. like someone else said you can change your sending unit, it wouldnt hurt, but you should also check your vacuum. turn your engine on and get a propane torch. dont lite it just let the propane out. run that propane along your intake carb and hoses. if the engine speeds up there you go vee leak.
     
  12. Lotsa_Faith

    Lotsa_Faith 1/2 ton status

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    i've changed the fuel filter not long ago at all. Where is the sending unit and all the vents that I need to check? I've replaced almost all of the vacuum hoses too. how much does a fuel pump run and whats involved in replacing it?
     
  13. dyeager535

    dyeager535 1 ton status Premium Member

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    Based on *my* fuel pump experience, I wouldn't replace it just because.

    My truck died on me on the way to work, then restarted ok. Got to work, parked it. Came back 8 hours later, drove a block, and it died. No fuel from the pump. Replaced, good as new.
     

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