Fuel Cutting Out- Help

Discussion in 'Fox 5.0 Mustang Tech' started by Treachery, Feb 4, 2013.


  1. Treachery

    Treachery Founding Member

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    1993 Mustang GT (see signature for mods)

    My GT was dynotuned 2 days ago.

    The tuner could not complete the tune because the fuel kept cutting out at 4000+ rpm. Engine needs more volume. At the suggestion of the tuner & the advice of others, i've upgraded the fuel injectors to 60lbs, upgraded my fuel pump to an Aeromotive 340, upgraded the fuel rails to a BBRC kit and upgraded the fuel lines to 3/8' inch.

    The upgrades were ineffective... In fact, the engine was running a little leaner than before.

    All other parts appear to be working correctly. The installation of the upgrades were checked- OK. Lines and hoses- OK. Engine making excellent power but when past 4000rpm, fuel cuts out. Tuner said that he opened everything up and the fuel injectors are working at 100% when the fuel cuts out. Checked ignition module- OK. Voltage is OK- new Optima battery.

    Tuner offered that the 60lb fuel injectors may not be what they appear to be since the fuel keeps cutting out. I disagree because with the 42lb injectors i had before, the engine was behaving the same way.

    I am thinking that if all is working as should be, the computer (A9L) might be the cause of this behavior. The tuner does not think so... Whatever the case may be, something is causing the fuel to be cut thus robbing me of lots of power at above 4000rpm.

    Has anyone experience this kind of behavior?

    Thank you.
     
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  2. Rick 91GT

    Rick 91GT SN Certified Technician Site Sponsor

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    That's a weird one, I assume the rpm is being measured through his tuning software and not looking at the stock tach? With the set-up you have you should have any fuel issues, did he give you any fuel consumption numbers? Ive never seen a A9L act that way, but a easy test would be swap it out with another one...chip will bolt right up and work.

    Could be the meter....What the MAF say, does it show anything funky at that rpm?
     
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  3. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Did you still have the needed pressure at your 4000 RPM mark? If so, then you don't have a fuel delivery problem. You may have a tune or injector quality problem that could be more expensive/time consuming than a fuel delivery problem.

    In order to maintain the flow rating of an injector used in an engine with pressurized induction, you have to increase the fuel pressure 1 PSI for every 1 PSI of boost. That means If you run 10 PSI boost, you need to run 50 PSI fuel pressure: 40 PSI base + 10 PSI additional to compensate for the boost.

    See http://users.erols.com/srweiss/#jcalc for simple programs to help you calculate the needed injector size and pressure.
     
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  4. tobalx

    tobalx Member

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    im just a noob here so im totally guessing here! but could it possibly be a regulater screwing up when it sees to much volume?? that is about the only thing you have not mentioned.
     
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  5. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Not likely. The regulator returns fuel to the tank to control pressure: the more it returns, the lower the pressure. You need a pressure gauge on the fuel rail to determine what the pressure is at any given time.
     
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