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Engine Miss - LX450 - From Below

Discussion in '80-Series Tech' started by tomlite, Feb 26, 2004.

  1. tomlite

    tomlite

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    1997 LX450 with 78,000 miles with Automatin Transmission.

    The temperature has been for 15° F. to 50° F. in the morning. The engine starts fine and goes smoothly to a steady fast idle of 1400 rpm. Within 15 seconds, I back out on a level drive about 60', and proceed foward underlight acceleration to a speed of about 20 mph for a distance of about 1/4 mile. During this time, the miss is very sporatic, lasting less than 1 second, almost as if the engine is running out of fuel, but disappearing almost instantly. When I stop, the engine idles smooth, but not as smooth as when the engine is warm. For the next 1 to 2 miles, the miss is still sporatic and only under mild acceleration. The miss doesn't start as soon as I start acceleration but happens after a 1 or 2 second lag. After 2 miles the engine runs smooth, accelerates smooth, Idles really smooth.

    One night I went out for about 5 hours, the outside temperature was about 5° F. The miss was as sporatic, but stronger.

    When warmer the miss is milder.

    I have replaced the Spark Plugs with Bosch Platinum about 4 months ago. I have recently replaced the Wires, Cap, Rotor, and Fuel Filter. The engine has 78,000 miles and burns less than 1 quart of oil in 2500 miles.

    Please feel free to stop by and drive this some morning.

    Thanks for your opinions,

    Tom
     
  2. ppc

    ppc M Go Blue

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    It would be a little easier on us if you didn't start a new thread or made a referenced to it.

    You didn't answer my question related to a miss or stumble. Sounds like a stumble where you loosing power based upon your description. My guess is the fuel system. Possible items are fuel filters but I doubt this as problem would be hot or cold. Others are fuel pressure regulator and the vacuum lines going to it. Also check other vacuum lines as well. Last it the fuel pump. You could try bypassing the fuel pump relay which will run the pump at full voltage. If the problem is gone, then the fuel pump needs replacement.
     
  3. Beowulf

    Beowulf

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    Tom,
    Did you go with the OEM heat range on the plugs or colder/hotter?
    Are the wires, cap, and rotor OEM?
    Did you notice the cold miss before or after the tune-up? If after, how long after?
    -B-
     
  4. cruiserdan

    cruiserdan SupportingVendor Emeritus Moderator

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    Air intake hose cracked?
     
  5. IdahoDoug

    IdahoDoug

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    When did this first start happening? It would be helpful to know. Something like "It started after I did the tuneup", or "It started after I got stuck in a mud pit and had to leave it out there overnight with water up to the doorhandles", etc. Not trying to be a wise guy, but this is key information. Good description of the problem, BTW.

    Can you get the miss to happen if you keep the truck stationary with the brakes and use light to moderate throttle settings just as if you're driving off as you describe above? If you can, we're onto something good.

    DougM
     
  6. Riley

    Riley

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    I bet a :beer: that Dan's got it nailed. Not that I'm trying to improve on my smart shopping skills but it's a sixth sense.

    Not sure why it would vary with temp of the motor or air but it's worth a very close inspection.
     
  7. PHAEDRUS

    PHAEDRUS

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    Dan is good but im guessing egr related vacum leak. hence the tem p making a difference and it being sporadic at start up.
    Dave
     
  8. cruiserdan

    cruiserdan SupportingVendor Emeritus Moderator

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    Good point Dave,

    And I was just speculating, no crystal ball. In either case it would be vacuum related which is what it sounds like (to me).


    :beer: D-