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Thread: Misfire after LS 327/327 engine swap. Do I need a HP Tune ?

  1. #1
    Potential Tuner
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    Jul 2015
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    Misfire after LS 327/327 engine swap. Do I need a HP Tune ?

    Hi all I am new to all this performance stuff and need some help. After reading your posts I sounds like you guys know how to tune modified engines so I would like to ask you for assistance.

    I have a 2000 GMC Yukon SLT 5.3 4WD.

    I recently replaced my stock 5.3 engine with a LS 327/327 engine. http://www.chevrolet.com/performance...nes/ls327.html

    I added a hughes 22-20L torque converter, and blocked of the EGR valve.

    The Truck runs better, more power and shifts OK. But is rough and misfires at idle and looses power on the highway.

    I replaced all spark plugs and leads, no improvement, no codes found when scanned.

    It runs rich, fuel consumption is high.

    It has only been driven from 1600 miles.

    I think it has major tuning issues, but I am a complete newbie to this whole car tuning thing.

    If there is someone on the forum who understands what may be wrong and how I could go about fixing it, I'll greatly appreciate their help.

    Does it need a HP tune or not, might there be something else wrong?

    Chevy327

  2. #2
    Tuner smokestack's Avatar
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    Jul 2011
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    West terre haute Indiana
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    It needs the right calibration for that engine. Yes.

  3. #3
    Potential Tuner
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    Quote Originally Posted by smokestack View Post
    It needs the right calibration for that engine. Yes.
    Thanks for the reply smokestack.

    Where do I get that calibration from Smokestack, do I have to get it from GM or find someone with a tech2 tool, or do I have to send out the ECU to be reprogrammed.
    I need a simple solution and have no direction on this.

    Sorry for my ignorance I have no clue about this who stunning thing. I wish I could learn it , but from looking at all those tables and graphs I looks like a nightmare to even thing of learning it, I bet it would take months to learn, and perhaps a couple of destroyed engines through trial and error.

    Look forward to your reply.

  4. #4
    Senior Tuner mowton's Avatar
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    Mar 2007
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    Florida
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    Quote Originally Posted by chevy327 View Post
    Thanks for the reply smokestack.

    Where do I get that calibration from Smokestack, do I have to get it from GM or find someone with a tech2 tool, or do I have to send out the ECU to be reprogrammed.
    I need a simple solution and have no direction on this.

    Sorry for my ignorance I have no clue about this who stunning thing. I wish I could learn it , but from looking at all those tables and graphs I looks like a nightmare to even thing of learning it, I bet it would take months to learn, and perhaps a couple of destroyed engines through trial and error.

    Look forward to your reply.
    Look to someone else doing the tuning either local or remote (see links below) if you can find someone who will lend you the cable...either HP Tuners or EFI Live in my case.

    Other assumption is the the swap/install is compatible (all sensors etc) with the previous setup.

    Ed M
    Last edited by mowton; 07-22-2015 at 06:22 AM.
    2004 Vette Coupe, LS2, MN6, Vararam, ARH/CATs, Ti's, 4:10, Trickflow 215, 30# SVO, Vette Doctors Cam, Fast 90/90, DD McLeod, DTE Brace, Hurst shifter, Bilsteins etc. 480/430

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  5. #5
    You will be best off to do a custom tune for the vehicle, there is no warranty to worry about so find a good tuner in your area. If you are near me in northeaster ohio PM me and I will be more than happy to help.

    You can go to your local speed shop, or hangout or cruisein and talk to people. They should be able to point you in the right direction.

    Short answer is yes you will need a tune for the combo / vehicle you are running.