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engine sputters and pops at highway speed

Discussion in 'GM Powertrain' started by gmc4life, Aug 6, 2007.

  1. gmc4life

    gmc4life New Member

    I have a 95 Chevy 1500 suburban with 94k miles.
    350 motor.
    Second owner.


    Problem:
    Truck runs well and shifts well under normal conditions.
    Just bought a 18ft pop-up camper. Camper weighs 2500 pounds unloaded. While towing up a grade on the highway using the cruise control, transmission downshifts to maintain speed and causes engine to stutter, sputter, pop, lag, and lose horsepower. Once past the hill, the engine runs fine and trans shifts back into overdrive.

    Solutions: (I've tried)
    I checked timing since a friend suggested spark-knock. The timing was advaced on this truck. Upon setting it correctly, same problem results, but with less frequency and only after the 3 hours of driving at operating temperature.
    Next I flushed the cooling system.
    I had the transmission flushed and new filter installed.

    Help:
    I need advice on what to check or replace next. I am thinking that a tune-up might solve this issue, but wanted to check with others before doing so.

    Thanks for reading.
    Matt
  2. Dj Friction

    Dj Friction New Member

    gmc4life.....

    A couple of things that I do when towing........I have a little heavier load. but take it out of OD when towing.....unless you are on flat ground.

    The next thing was when was the last time the plug wires were replaced, my wife's blazer 95 4.3 with 160K had a similar thing when you can on the flat in OD found that the wires (not really that old) was losing conductivity. A fresh set changed the whole running picture.

    Worth a try???
  3. CaJuN625

    CaJuN625 New Member

    Maybe the fuel delivery system?

    I'd consider TOP ENGINE CLEANER for the intake, a WHOLE BUNCH of fuel injector cleaner for a few tanks, a new fuel filter ... possibly a new pump. I'm thinking that you COULD be having issues delivering the amount of fuel the engine requires: more fuel for towing plus higher RPMS plus climbing a hill. Under normal conditions, you may be within the capabilities of your old fuel system. Under heavier loads, you might be JUST outside of it.

    This is ALL a big MAYBE. Just a thought.
  4. unplugged

    unplugged New Member 1000 Posts

    Yes, plugs, wires and carbon deposits are suspects. Easy enough to remedy. Seafoam from your NAPA dealer for the carbon deposits. Then examine the plug wires for burns or evidence of a short. Cheaper plug wire sets are a compromise since the lengths aren't exact and any contact with the exhaust manifold will shorten their life. If you haven't changed the plugs in awhile, now might be a good time to put in a set of platinum plugs.
  5. racer14

    racer14 New Member

    I like the fuel volume check idea, too. Even within the specified pressure range, a tired pump may not supply enough volume. If a fuel filter replacement helps, pump may be fixin' to say "Seeya".
  6. gmc4life

    gmc4life New Member

    Thanks for the advice, I will start with a tune up and go clean intake manifold next. I am not comfortable changing the fuel pump out, but will have it done as a last resort. I am so glad I found this forum. Thanks for all the advice!
    Matt
  7. ProzacKid

    ProzacKid New Member

    If you're running a '95 with that many miles I would definately suggest that you do a tune up.
  8. ProzacKid

    ProzacKid New Member

    Oh, by the way.

    :sign0016:

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