What is Fuel Cut

Posted by crankbender, Mar 18, 2005

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  1. crankbender

    crankbender Proven Member

    1,167
    6
    Joined Apr 15, 2002
    houston, Texas
    Ok here is the skinny I will tell you all about fuel cut hopefully for everyones benefit (My grammar is off tonight work with me here).

    Take out a pencil cause this is my kung fu and it is strong!!! :thumb: (anybody name that crappy movie?)

    I will try and step through this slow so everybody can understand what is going on.

    WHAT IS FUEL CUT?
    Fuel cut is actually a removal of the the injector firing signal from the ECU. This is to say that your engine computer doesn't put fuel in the engine, hence the name.

    WHAT CAUSES FUEL CUT?
    Despite the rumors of fuel cut being caused by too low of fuel pressure, too small of injectors, high flowing exhaust, high flowing intake, or large turbos fuel cut is not directly caused by any of these. Fuel cut is actually caused by the ECU seeing more air entering the engine than it was originally programmed to use. This likely cooresponds with an injector duty cycle which is unsafe or unattainable. So basically fuel cut is caused by the MAF seeing too much air. Don't ask what too much air is....

    WHY DO WE GET FUEL CUT?
    Since fuel cut is caused by the ECU seeing too much air we get fuel cut by increasing the air flow through the MAF.

    WHAT CAUSES TOO MUCH AIR TO BE SEEN BY THE MAF?
    Many things can cause this. basically anything you do to the engine to make more power increases the airflow...way to many to list here.

    SHOULD I GET RID OF FUEL CUT?
    NO NO NO NO NO...Do not use any device to eliminate fuel cut. Fuel cut is there for a reason. If you are hitting fuel cut the ECU believes that you are moving more air than the fuel system can safely deliver. If you are having to eliminate fuel cut with some sort of defender either you have an inadequate fuel system, inadequate tuning tools, or a leak somewhere.

    WHY DO LEAKS CAUSE FUEL CUT?
    Since fuel cut is caused by air flow and not actual AFR lost air can cause fuel cut.

    SO HOW DO I PREVENT FUEL CUT?
    This really isn't that hard. You have to SAFELY reduce the air the ECU sees. This means to deliver more fuel to the engine (assuming you are shooting for the right AFR) per air count. To do this you must increase the injector size (fuel flow per air count) and then use an new ECU program or AFC to decrease the air count accordingly. Not going to get into tuning now.

    WHAT SHOULD I NOT DO TO PREVENT FUEL CUT?
    Do not decrease air counts without adding more fuel per air count. This will cause you to just run lean all the time and cause exactly what fuel cut tries to prevent. So....
    DO NOT PUT IN A FUEL CUT DEFENDER.
    DO NOT RUN A 2G MAF ON A 1G WITHOUT A WAY TO BALANCE IT OUT.
    DO NOT JUST LEAN OUT YOUR AFC TO UNSAFE AFRs.
    DO NOT TURN DOWN YOUR GM MAFT TO UNSAFE AFRs.
    DO NOT TRY AND PUT IN LARGER INJECTORS WITHOUT FUEL MANAGEMENT.
    DO NOT TRY TO UP THE FUEL PRESSURE WITHOUT FUEL MANAGEMENT.


    Does this help yall a bit?
     

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    DavidJamesDSM and doubleclutch like this.
  2. wret

    wret Proven Member

    2,695
    56
    Joined Jul 3, 2003
    Bel Air, Maryland
    For more information and lots of discussion on fuel cut, go here. This is a combined thread with most of the discussion on the topic since 2002. A lot of misinformation has been circulated on the topic and much of it has been deleted from the thread. If you have more questions or information, feel free to add to the existing thread.
     
    bryce_gst98 likes this.

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