Runs fine until it shifts into second...

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Timmer_71, Apr 10, 2003.

  1. Timmer_71

    Timmer_71 Registered Member

    Aug 2, 2002
    Likes Received:
    Zeeland Michigan
    I can't figure this one out, It starts up fine and runs great until it shifts into second then it starts to miss and the whole truck starts to shudder when it shifts into second then when I get into 3rd it's even worse. I've replaced plug's,wires,cap & rotor, checked timing etc...
    Today I hooked a vacuume guage up to it and ran it up to my windshield and held it down with my wiper so I could see what it was doing as I went down the road and once again it is just fine at idle (steady at about 18 in./Hg) and when I step on the gas it of course drops down and comes right back up to 18, but when I go down the road and it shifts into 2nd gear it starts to jump back and forth from about 15-20 in./Hg and it feels like I am running on about 6 cylinders, then when I hit 3rd gear it jumps back and forth from almost 0 to 20+ in./Hg and it is running so bad I can hardly hold my speed.
    What do you gut's think is causing this?
  2. Okiemuddog

    Okiemuddog 1/2 ton status

    Mar 3, 2003
    Likes Received:
    Guthrie, Oklahoma
    Just my 2 cents

    Try changing your fuel filter or fuel pump, it might be starving for gas under a load.
  3. Thunder

    Thunder 3/4 ton status

    Jul 20, 2000
    Likes Received:
    Northeast Nevada
    If you have HEI I would guess your Dist module may be going out or possibly the magnetic pickup coil.
    If you have points ignition, a bad condenser will cause those problems.

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