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motor still runs after ingnition is killed...help please

Discussion in 'The Garage' started by 01maroonz71, Jan 24, 2007.

  1. 01maroonz71

    01maroonz71 1/2 ton status

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    well i just got the truck last night and about one in four or five times this will happen...when i shut the truck off....it fires right back up w/ the key out of the ignition and runs for like 1 or 2 seconds. maybe it's running rich and has fuel in the cylinders after i kill it...could that be it???? anybody have a clue???? thanks!!!!
     
  2. barneybasher1010

    barneybasher1010 1/2 ton status

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    timing is off
     
  3. 01maroonz71

    01maroonz71 1/2 ton status

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    would this kill my gas mileage???? also...the truck never backfires, and mostly fires right up no problem.....aren't those signs of timing off??? thanks!!!!
     
  4. 1977k5

    1977k5 3/4 ton status Vendor

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    Its one of 3 things. The timing could be off, the idle could be set too high, and the combustion chambers could be fouled with carbon.
     
  5. rcamacho

    rcamacho 1/2 ton status

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    You may need a diode on the alternator activiation circuit to prevent run on depending on your ignition system (MSD, etc)
     
  6. 01maroonz71

    01maroonz71 1/2 ton status

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    ok...i know i have a mallory ignition/dist. and i know this motor was built really well. I thought about runnin some seafoam through it to see what would happen...anybody had experience with this on carb'd motors...i used to use it on all my EFI trucks.


    i just drove it to the bank/gas station...and it didn't do it either time i started the truck, so it only does it sometimes.
     
  7. dremu

    dremu Officious Thread Derailer Premium Member

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    It's called "dieseling" as it runs without the spark plugs. As others have said, check idle speed and timing. Seafoam won't fix either :)

    -- A
     
  8. 1977k5

    1977k5 3/4 ton status Vendor

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    Seafoam will, however, fix carbon buildup. The carbon buildup causes hot spots in the combustion chamber which can cause dieseling.

    I have seen carbon be the culprit more than the other two.
     
  9. dremu

    dremu Officious Thread Derailer Premium Member

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    Shh. I was trying to get the newbie to check his motor :rolleyes:

    -- A
     
  10. 01maroonz71

    01maroonz71 1/2 ton status

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    alright...im mediocre at doing motor work, i've done head gaskets, and so on...butnothing internal in the block but i am definately learning. somebody above stated carbon build-up and that is why i thought of sea foam...i just haven't used it on a carb'd motor...just EFI...also, i have never adjusted timing, so that will be new to me also...but i am more than willing to learn. thanks alot guys!!!!
    ~Dave
     
  11. dremu

    dremu Officious Thread Derailer Premium Member

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    My experience with dieseling is that it's a combo of timing and idle speed ... so you'll need to tweak both. Too high an idle speed with the timing too advanced, I think...

    OTOH, if *I* can figger it out -- magic 9/16" dizzy wrench and a flathead screwdriver -- anybody can do it =))

    -- A
     
  12. beater_k20

    beater_k20 Banned

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    seafoam will fix carbon deposits in the cylinders, which create hot spots, and often cause dieseling. so it very well could "fix" the problem, but it'll be back, because something is wrong causing the carbon deposits to form in the first place.
     
  13. beater_k20

    beater_k20 Banned

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    :doah: he beat me to it.
     
  14. 01maroonz71

    01maroonz71 1/2 ton status

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    awesome guys...i will seafoam her...then work on adjusting the timing one way or the other...can i do this without a timing light, or do i need one???? somebody told me i can just loosen the dizzy and turn it a tad one way or the other...tighten it up, then start the truck to see if it runs better....but that sounds like a bit of ghetto engineeering....i think ill just buy one and figure out what i need to do to time it correctly. thanks again for all your help!!!
     
  15. dremu

    dremu Officious Thread Derailer Premium Member

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    Timing light will tell you where it is, but you'll end up tweaking it by hand (along with your idle speed!) ... so a bit of both.

    -- A
     
  16. 01maroonz71

    01maroonz71 1/2 ton status

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    well, i seafoamed her and it helped some...and i turned down the idle about 3/4 of a turn, but couldn't tell at all. one thing i did notice was that the vacc advance on the dist was hooked up to nothing...
    another note is that when the truck has been driven, then i go to back it into my parking spot, it kicks real hard in reverse like it's reved up to high....and when idleing it's at like 900rpm, then i hit the gas a few times, and the idle goes down to 400 or so....


    oh yeah, on a side note, it's got mallory dist/igniton and a holley carb(doulbe pumper) 650 i assume since it's a 350. it also has a very very mild cam if that would matter about the vac advance. thanks for your help guys....i will mess with the timing tomm. since i got off so late tonight.
     
  17. diesel4me

    diesel4me 1 ton status Premium Member

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    timing ....

    I'd bet if your running without the vacuum advance hooked up,that the ignition timing has been advanced a lot to make up for the lack of vacuum advance..re-set the timing after hooking the vacuum advance back up--you can use manifold or ported vacuum (that refers to where the hose gets its vacuum from,above the carb's butterfly's or below--.

    Over advanced timing encourages dieseling,so does a higher than needed idle speed..also carbon deposits or a valve getting hot enough to ignite the fuel instead of the spark plug too..

    Some motors run better with ported VS manifold vacuum,trying both and test driving it is the best way to tell)..be sure the vacuum advance works,and that its diaphram isn't ruptured--that might be why it wasn't connected!..quick way to tell if its working is to hook the hose to manifold vacuum while its idling--if the motor speeds up some,its working..:crazy:
     
  18. 01maroonz71

    01maroonz71 1/2 ton status

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    awesome diesel...so if i plug it up to the manifold, then it will idle higher than it is now, or are you saying with hit hooked up, when i un-hook it it wil idle higher....
    thanks again for all ya'lls help...im off to the auto store to get some vaccuum hose.
     
  19. diesel4me

    diesel4me 1 ton status Premium Member

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    vacuum sources..

    "Ported" vacuum is when you hook the hose to a nipple on the carb above the butterfly's--there will be no vacuum at idle,and when you rev it up you'll feel suction..."Manifold" vacuum is below the carb's butterfly's,and there will be vacuum pesent at idle,and it'll die off as its revved up...you can use a finger over the nipple to see which one has vacuum at idle..

    If the vacuum advance is working,then the motor should idle faster when you hook the hose to manifold vacuum..you'll have to set the timing with the vacuum advance unplugged to specs,(I gave the wrong advice in my last post--time it while its dissconnected!)--then attach the hose and try driving it..

    I have found since I live near sea level,I can run a bit more advanced than stock specs without pinging,and most of my trucks ran better and got better gas mileage with manifold vacuum,even though most Chevy's used ported vacuum from the factory (depending on year,emissons,etc)..you need to try both ways, to see which one works best for your engine and altitude...you'll notice a big difference in power with it timed right, and with the vacuum advance working,and gas mileage too.:crazy:
     
  20. 01maroonz71

    01maroonz71 1/2 ton status

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    thanks alot man...your my hero. haha...im gonna go try it out now. and work on timing it tomm. wish me luck. haha
    ~Dave
     

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