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Thread: How to compensate for larger injectors?

  1. #1
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    Default How to compensate for larger injectors?

    I've installed 40% over injectors, but I'd like to tune the truck in such a manner that they behave as stock injectors would. I guess "dial them back". I just rebuilt the engine and would like a bit of a break in period before I pour the coals to it. Can anyone help me? Which tables do I change? Do I need to do anything with the pilot injection? Any help is appreciated!
    Last edited by Zorganov; May 16th, 2013 at 11:27 PM.

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    There's got to be somebody out there that can help me with this! Please Please!

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    I'm in the same boat you are. I Just rebuilt my motor, 60% over nozzles, bigger turbo, etc. What I did right off was just adjust B0201 MAF Flow Rate. This allows you to pull back fuel all over the board. When you adjust the numbers down a little the ecm reads less air moving across the sensor & in turn injects less fuel. Easy way to clean up smoke and fuel rattle while you figure it out

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    Lifetime Member THEFERMANATOR's Avatar
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    Quote Originally Posted by Meshanic View Post
    I'm in the same boat you are. I Just rebuilt my motor, 60% over nozzles, bigger turbo, etc. What I did right off was just adjust B0201 MAF Flow Rate. This allows you to pull back fuel all over the board. When you adjust the numbers down a little the ecm reads less air moving across the sensor & in turn injects less fuel. Easy way to clean up smoke and fuel rattle while you figure it out
    Adjusting the MAF rate is simply for smoke control. You need to compensate your injection pulse width tables for larger injectors FIRST! Figure out your injector latency and subtract that from your pulse width tables, then make your percentage changes for the oversized nozzles(a word of warning, a 60% larger nozzle will not require 60% less pulse width), then add the latency amount back to your tables. Next you need to compensate for timing, and then your limiters.
    1995 GMC 2500 SUBURBAN powered by 01 DURAMAX/ALLISON, little of this, a little of that,
    DIAMONDEYE 4" exhaust, CORSA muffler, AFE stage 1 dry filter, custom tuning by me, KENNEDY single pump and pump rub kit.

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    Quote Originally Posted by THEFERMANATOR View Post
    Adjusting the MAF rate is simply for smoke control. You need to compensate your injection pulse width tables for larger injectors FIRST! Figure out your injector latency and subtract that from your pulse width tables, then make your percentage changes for the oversized nozzles(a word of warning, a 60% larger nozzle will not require 60% less pulse width), then add the latency amount back to your tables. Next you need to compensate for timing, and then your limiters.
    Thanks Ferm. I'm still figuring this out myself. The MAF adjustment idea I got from Zach at Starlight Diesel. It allowed me to get mine to quit rattling at low boost and cruising.
    I did the math & found in order to get these 60 overs to flow more like stock I had to subtract 37.5%.
    Here's how I came up with that number. Say my fuel delivery per stroke is 50 mm3 and my commanded fuel rail pressure is 100 mpa, my stock main injection pulse is 776.
    60% of 776 is 465.6. Added that equals 1241.6. In order to bring 1241.6 back down to 776, I subtract 37.5%.
    Of course that is not accounting for the injector latency that Ferm mentioned.
    Ferm is there a formula or table I can use to figure latency? I found on another thread where you said it was about 100 usec. Was that on a stock injector?
    I think that is an important part of the equation I never considered.
    Last edited by Meshanic; May 21st, 2013 at 02:24 AM.

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    Quote Originally Posted by Meshanic View Post
    Thanks Ferm. I'm still figuring this out myself. The MAF adjustment idea I got from Zach at Starlight Diesel. It allowed me to get mine to quit rattling at low boost and cruising.
    I did the math & found in order to get these 60 overs to flow more like stock I had to subtract 37.5%.
    Here's how I came up with that number. Say my fuel delivery per stroke is 50 mm3 and my commanded fuel rail pressure is 100 mpa, my stock main injection pulse is 776.
    60% of 776 is 465.6. Added that equals 1241.6. In order to bring 1241.6 back down to 776, I subtract 37.5%.
    Of course that is not accounting for the injector latency that Ferm mentioned.
    Ferm is there a formula or table I can use to figure latency? I found on another thread where you said it was about 100 usec. Was that on a stock injector?
    I think that is an important part of the equation I never considered.
    For LB7 I found 100 usec to be pretty close. I found it by playing around with the minimum pilot quantity. I set the pilot to 0, and then started dropping the minumum pilot quantity until I found that it no longer worked(roughly 92-95 usec, so I use 100 to be safe). Not an exact science, but it got me pretty dang close. Makes for some wierd looking changes to the fuel table when you look at it with latency figured in, but when you subtract latency it all makes sense. Also you will find that at idle you will subtract a diffrent amount than you will up top as the changes are not perfectly linear.
    1995 GMC 2500 SUBURBAN powered by 01 DURAMAX/ALLISON, little of this, a little of that,
    DIAMONDEYE 4" exhaust, CORSA muffler, AFE stage 1 dry filter, custom tuning by me, KENNEDY single pump and pump rub kit.

  7. #7
    Senior Member Quinton's Avatar
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    Default How to compensate for larger injectors?

    Subd.
    [/SIGPIC]
    2005 duramax LLY, 12.75 on stock motor/fuel, 68mm vgt built trans.
    Built motor by me, built trans, EFIlive by me, dual fuelers, 80% injectors.

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    Thanks Ferm. That's some good info.

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    subd

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    Ok got mine right where I want it. Pulled 100 usec from the pulse width as my latency, pulled my desired percentage and then put 100 usec back in. 37.5% worked great for my 60 overs. Once I got that it all started coming together nicely. Using the Josh H timing calculator made timing a breeze. Just used the same strategy I've been using for years with the new pulse width numbers.

    I am loving tuning this thing! My street tune never exceeds 15' of timing & runs high 13's on a single CP3 with no lift pump. I have WAY less rattle than an LBZ with an edge. There is nothing like custom tuning

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