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Thread: Low boast

  1. #1
    Join Date
    Nov 2001
    Location
    oxford al usa
    Posts
    4

    Default Low boast

    98 6.5 3500 HD. Have replaced boast solinoid on valve cover. Vacuum pump and turbo. Max boast under load is 4 Lbs. I give up does anyone make a mechanical control that fits this truck? Thanks for help!

  2. #2
    Join Date
    Apr 2001
    Location
    Newberg Oregon
    Posts
    12,282

    Default

    HI
    Welcome to TDP

    There are several things that can cause low boost pressure.
    You have eliminated some key ones, but one big issue that comes to mind is the exhaust system.

    How many miles on the rig ???

    Has the CAT/soot trap ever been changed or removed entirely ???

    A plugged CAT will choke things up to the point that turbo can't spin fast enough to do much.

    YES
    There are things that can be done to get the boost up.

    A mechanical waste gate controller is available (Called a turbo master)

    In order for these to work properly you will need to get the ECM reflashed with the proper software.

    First off, make sure the exhaust system is free flowing.

    A good 3-1/2 to 4 inch system from the downpipe back is needed.
    The original CAT can be removed if you are not having to deal with emissions testing.

    Once the exhaust is free flowing the rest is a snap.

    Adding performance goodies to a plugged stock system will do no good at all.


    Let us know what the truck has had done to it.

    Robyn
    (1) 1995 Suburban 2500 4x4
    (1) 1997 Astro
    (1) 2005 Suburban (Papa Smurf)
    THIS IS BOW TIE COUNTRY

  3. #3
    Join Date
    Nov 2001
    Location
    oxford al usa
    Posts
    4

    Default

    Truck has 286k miles,186K on present motor. 3 1/2 straight thru exhaust. Runs great uses no oil. Truck is heavy with service body and tools. Pulls balers regular at 4 to 6 K Lbs.

  4. #4
    Join Date
    Apr 2001
    Location
    Newberg Oregon
    Posts
    12,282

    Default

    Great.

    With the 3-1/2 pipe there is little issue with restriction.


    Make sure you are getting about 22"of vacuum at the waste gate actuator.

    Make sure the waste gate move freely with the engine off.

    You should see 26" vacuum at the vacuum pump itself.

    If all you are seeing is 4-5 psi boost then you are actually not too far off of stock settings.

    Get the ECM FLASHED to use a mechanic waste gate control and push the fuel up a bit.

    Without the ECM flash the thing will scream and defuel when the boost hits about 8 or so.

    Set the mechanical gate control so under a hard pull the thing yields 10 psi no more.

    Be sure you have an exhaust gas temp meter in the beast as well..
    No more than 1000F at the outlet of the LH manifold under a hard pull.

    Do not install the EGT probe after the turbo as it is way too cool by then.

    1000F at the ports is max temp.

    Going up into the land beyond will melt things in these engines if allowed to run more than a few seconds at high temps.


    A good reprogrammed ECM and 10 psi boost will get about all the 6.5 can live with.


    Good luck

    Robyn
    (1) 1995 Suburban 2500 4x4
    (1) 1997 Astro
    (1) 2005 Suburban (Papa Smurf)
    THIS IS BOW TIE COUNTRY

  5. #5
    Join Date
    Jan 2001
    Location
    New Hampshire - Live Free or Die
    Posts
    6,057

    Default

    Make sure the hoses on the vacuum valve aren't reversed. It's been a while, but I think the vacuum pump connects to the port with the restrictor in it and the wastegate actuator connects to the unrestricted port.
    The Constitution needs to be re-read, not re-written!

    If you can't handle Dr. Seuss, how will you handle real life?

    Current oil burners: MB GLK250 BlueTEC, John Deere X758
    New ride: MB GLS450 - most stately
    Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6, '90 MB 350SDL, Kubota 7510

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