Why do I have to push gas pedal to the floor or half way on 1989 ford Mustang LX 5.0 for it to start up? NEED HELP pissing me off lol?

I'm finishing a 1989 Mustang LX 5.0 for my cousin and right now it will only start up when you push the gas peddle to the floor or half way also when it does start it won't rev past around 3k to 4k RPM then sounds like it's flooding out.

Any help would be great full!


Stock 302 5.0 EFI block & bore

AFR Aluminum heads

Comp Rollor rockers


Elderbock upper & lower intake

Bigger MAS air

Bigger Throttle body

HV fuel pump

Big injectors

Fuel PSI regular

Everything is matched up right

A few other things I may have left out just ask & I'll get back to you soon as I can also I can send pics


3 Answers

  • paul h
    Lv 7
    5 years ago
    Favorite Answer

    Do you run a modded computer chip or programmer kit? So you're running bigger injectors which means the computer is putting more fuel into the engine than needed for the same injector pulse if you have not remapped the PCM/chip. The computer doesn't know the injectors are bigger so it opens them for the same duration as a smaller injector...ergo, more fuel is being added. More fuel means you have to open the throttle more or fully for enough air to get in to allow starting, idle, etc... and may cause flooding the engine. The stock IAC may not be able to handle enough airflow at closed throttle for normal starting with the bigger injectors....nor should it need to. Modding engines is OK but with FI and computers, you also have to mod or tune the way the computer calculates injector pulses, fuel maps/trims, IAC counts, etc..for proper starting or engine operation.

    Put the stock injectors back in and try it....and possibly the stock TB which may alter stock airflow patterns/flow rate for the computer to handle ...or reprogram the chip/computer for the various mods or get an adjustable programmer so you can tune injector pulses, etc..


    Edit: Just an odd thought but I've heard of some situations where the TPS was wrong style with voltage readings in reverse of what it should be or hooked up/connected backwards from normal which would cause the computer to think the throttle is wide open when actually closed....and vice versa....which can cause the issues you are having. Check the TPS to make sure it's the correct one and installed properly/aligned and wired up correctly.

  • 5 years ago

    Perhaps it's a leaking fuel injector and the motor is flooded. Holding the pedal to the floor while cranking the motor over shuts off the fuel injectors. Try pulling the spark plugs and see if they are wet before starting the motor.

    Source(s): Mitsubishi Master Tech
  • Anonymous
    5 years ago

    sounds like something either in the fuel system or the throttle linkage

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