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  1. #1

    Default 86 maf conversion issues

    Converted my 86 gt to MAF. After i did this it will not idle,and there is no throttle response. If i pump the throttle after i stop there is like a 1/2 second delay or so and then the rpms jumps up then dies instantly. I put in a A9L with a chip from a well known tuner. Been over the wiring for the conversion 3 times now. I have a brand new walbro fuel pump brand new lines brand new fuel filter brand new tank brand new kirban fpr brand new kirban fpr gauge. When i cycle the key on i barely see any fuel pressure and it drops back to nothing almost instantly. When i get the car started i try to adjust the fuel pressure and seems like nothing change pressure wise on the gauge. Ive been told possibly a bad ECM? Car ran perfect as SD. If anyone can help with some trouble shooting that would be great. Is there a way to test all circuits are working on the ECM?

  2. #2

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    there are only four wires to pin as long as the two going to the computer are correct and you have a good connection that should be fine.
    I think the other two are iginition hot and ground.

    I think start by removing the chip and running the computer by itself.
    How big are the injectors? 24s it should run fine for testing
    are the MAF and Chip matched to the injectors? stupid question but I had to ask.



    then triple check the wiring to the computer. The pins can be hard to seat in sometimes, did you get new ones?


    after all that worry about the computer.

    The a9l doesn't control fuel pressure, it assumes you have 43 psi give or take.
    do you have good fuel pressure when you start and run the car?

    in the tank return line there is a rubber valve that slows the fuel from going back to the tank. but that shouldn't have an effect on running just how fast the fuel returns to the tank. sometimes those get ripped or wear out. It may prevent you from building pressure with just a key on also.
    Is your filter backwards? Not sure if some restrict flow when backwards or not.

    I think figure out fuel system first probably something simple, then worry about conversion

  3. #3

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    I would definitely remove the chip like suggested before doing any trouble shooting to rule the tune/chip out as a possible cause of your issue plus does your Mustang have the same exact parts on it as the car which the chip was tuned for?? Eliminate it as a possibility.

    It wouldn't have anything to do with a possible fuel pressure issue,but along with the ecm & wiring changes,did you also remember to disconnect the vacuum hose from the map sensor,plug/cap the vacuum hose/intake vacuum fitting and leave the vacuum port on the map sensor open to atmosphere?? This is a must.

    You can also run tests on the maf sensor and wiring to verify the parts are in perfect working condition.The following link will help.Make sure the sensor is clean too.Use maf cleaner only,not carb or brake cleaner.
    https://easyautodiagnostics.com/ford...sensor-tests-1

    Some aftermarket adjustable fpr's dont have a check valve and if so will not hold pressure after the key/engine is shut off.This could be one reason for the immediate pressure drop after shutdown. If,& only if,your fpr has a check valve & its bad,it will cause the immediate drop.If your fpr does Not have this check valve,the following test wont work,but if it Does have one,turn the key on/engine off,take a pressure reading,turn the key off and let pressure drop,pinch a soft section of the fuel return line closed (using vice grips & a rag for hose protection) then run the same exact test like above.Does pressure hold??If yes,the fpr is defective.If no,the fuel pump check valve is defective.

    The following will only affect the engine when you're slowing down to stop,but if you fail to run the wires related to the maf conversion which are used for the vehicle speed sensor,this can cause erratic idling and stalling when you're coming to a stop (in manual applications only),but if the problem is occurring at idle only,this wiring issue wouldn't be at fault.

    For future reference,if you ever replace the iac valve with a new or remanufactured unit that has a diode built into it & you develop a rough or erratic idle,make sure you cut the diode out of the iac valve portion of the fuel injector harness wiring if its an 86-88 Mustang oem harness because the harness diode and the iac valve diode will compete with one another and cause the symptoms listed.86-88 had a diode on the harness with no diode in the oem iac valve while 89-93 had no diode on the harness with a diode in the oem iac valve.Most/all reman units will have the diode built in.

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