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Butchman's avatar
Butchman
Explorer
Mar 26, 2018

8.1 vortec

Have a 2005 dolphin 8.1 vortec will idle and run fine in park but when in drive misses and doesn't have any power. No check engine lights any ideas

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  • Isaac-1's avatar
    Isaac-1
    Explorer
    Mar 27, 2018
    A couple of points to check are the fuel pressure regulator, I think they may have changed it up some in 05 or 06, but on my 02 model it is at the back of the engine on the drivers side by the fuel rail. There is no fuel pressure sensor in the 8.1 so the computer assumes the fuel pressure regulator is doing its job, and assumes the fuel pressure is always right. So a vacuum leak or a bad fuel pressure regulator could cause the fuel trim to go bad. Also check the spark plug wires, the 8.1L vortec is notorious for burning through spark plug wires if the coach manufacturer did not provide enough ventilation to the engine compartment.
  • RCMAN46's avatar
    RCMAN46
    Explorer
    Mar 27, 2018
    Get a code reader.

    I just finished a Trailblazer that would not set the check engine light but did have a pending code for a misfire. Finally got a check engine light after a couple weeks and it was a bad coil pack.
  • Hank_MI's avatar
    Hank_MI
    Explorer
    Mar 28, 2018
    I'd go with a bad coil pack or spark plug wires. I haven't had the problem but a number of people have had issues with burnt plug wires.
  • rgatijnet1's avatar
    rgatijnet1
    Explorer III
    Mar 28, 2018
    A known problem is burned spark plug wires, especially on the rear most cylinders. Many people have replaced their ignition wires with Taylor Extreme silicone wires which can handle the heat better. Also you want to make sure that you have the heat shields on the plugs and the wires.
  • wa8yxm's avatar
    wa8yxm
    Explorer III
    Mar 28, 2018
    I have an 8.1 Vortec and my wife heard NOTHING wrong, but I heard a slight missfire and noticed the same loss of power and MPG you cite.

    Went to professional who found rodents had knawed some of the ignition PRIMARY (12 volt) wires and a bit of tape and solder and I was 100$%
  • Smitty77's avatar
    Smitty77
    Explorer
    Mar 28, 2018
    Rodents! Why does it always have to be rodents?!

    (Sorry, the DW had Indiana Jones on last night, and the snake scene was fresh in my mind:)! Seem the same disgust he had for the snakes, would fit my mood if I had found chewed wires!!)

    OP - Do the easy things first. Borrow a reader and plug it in for any codes. Chase down the spark plug wires for damage. (I know at least 10 people who had 8.1 spark plug wire problems...)

    And please close the loop back when you find root cause - as it might help others in the future:)!

    Best to you and all,
    Smitty

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