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Thread: Gen1 3.5EB LTFT's out of whack after new shortblock.

  1. #1
    Potential Tuner beavis's Avatar
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    Gen1 3.5EB LTFT's out of whack after new shortblock.

    Hey guys,

    Being this is more of a finesse troubleshooting issue, I figured I'd seek out your guys' help in determining why my LTFT's are so negative. To be fair, I'm unsure as to what they were on the original motor as I never had a reason to log them.

    Since shattering a piston skirt on the original motor, I had a forged shortblock built, had the heads pocket ported and cats deleted and re-assembled the motor, and am currently working with an excellent tuner to get it all straightened out.

    The main issue I'm having that has us concerned is the LTFT's are ~0.88 and .92 for banks 1 and 2 respectively - not good. The truck got brand new OEM injectors when I did the motor and it runs great. Apart from some knock on the hit, it pulls very well for a stock turbo truck and I'm pleased with the way it drives under almost all conditions. These negative LTFT's have me concerned, though. It runs too good to have leaking injectors, and I'm just out of ideas as to why this thing is pulling so much fuel at idle and cruise.

    I have logs galore if anyone is interested in viewing. I just don't know enough about the modelling and tuning aspect to fully understand what changes I've made - or need to make to get the trims back in check. My tuner and I agree that porting the heads shouldn't have as drastic an effect on fuelling (if anything the truck should be adding fuel for the flow increase I would think).

    Vacuum and exhaust leaks, although they would typically result in a positive LTFT reading, are nonexistant.


    Any advice would be greatly appreciated, thank you in advance.

  2. #2
    Advanced Tuner LastPlace's Avatar
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    Post a tune and log if you would like help

  3. #3
    Potential Tuner beavis's Avatar
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    Quote Originally Posted by LastPlace View Post
    Post a tune and log if you would like help
    I can post a log via Dropbox when i get home, will that work?

  4. #4
    Advanced Tuner LastPlace's Avatar
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    You can just post it and the tune on the forum here.

    Also know that you can't tune around a physical problem like some being physically wrong with your engine.

  5. #5
    Potential Tuner beavis's Avatar
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    Quote Originally Posted by LastPlace View Post
    You can just post it and the tune on the forum here.

    Also know that you can't tune around a physical problem like some being physically wrong with your engine.
    I'm aware of that. I'm hoping some more experienced eyes might be able to point me in the direction of a mechanical fault, even though it drives fine.

  6. #6
    Advanced Tuner LastPlace's Avatar
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    Contact your engine builder or your mechanic to help diagnose what is physically wrong with it.

    hptuners forum won't be much help to you.

  7. #7
    Potential Tuner beavis's Avatar
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    Quote Originally Posted by LastPlace View Post
    Contact your engine builder or your mechanic to help diagnose what is physically wrong with it.

    hptuners forum won't be much help to you.
    Hey man, I get it. I am my mechanic, I put the motor together once the shortblock showed up at my house. The reason why I'm posting here is because the truck runs great, there are no perceivable mechanical issues whatsoever. I'm hoping through logs perhaps someone might be able to spot something out of the ordinary, is that not appropriate for this forum?

  8. #8
    Advanced Tuner LastPlace's Avatar
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    Quote Originally Posted by beavis View Post
    Hey man, I get it. I am my mechanic, I put the motor together once the shortblock showed up at my house. The reason why I'm posting here is because the truck runs great, there are no perceivable mechanical issues whatsoever. I'm hoping through logs perhaps someone might be able to spot something out of the ordinary, is that not appropriate for this forum?
    The short answer is, no.

    Out of courtesy (due to your low post count), I explained how the forum works.

    If you are tuning your vehicle, Post a tune and log(s)

    Or have your tuner post his/her tune file and log(s)

    Hope this helps

  9. #9
    You changed the volumetric efficiency of the engine when you ported the heads. A larger port will yield less port velocity at lower loads. Therefore, less air gets into the chamber due to less of a "ramming" effect with lower port velocity. In short, what you are witnessing is very common with speed density vehicles. Just my thoughts on the issue, anyway.