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Thread: speed density mode questions

  1. #1
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    Default speed density mode questions

    Hey guys if I install larger injectors and I'm running in spees density mode with a 14.7 air/fuel set will it auto adjust for me with the bigger injectors upon installation or will I have to adjust the main scale? Anything else to adjust? Got 870cc injectors. Can't find this in my manual

  2. #2
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    Default Re: speed density mode questions

    It will not be able to auto-adjust enough. If you want to run 14.7, I suggest you turn off all Part Throttle Tracking and let the 7M ECU do it's job. It is very good, and very stubborn and persistent about maintaining that ratio, lol. :-) You must have a narrowband O2 sensor still installed for this to work.

    Main scale works by adjusting the overall amount of air that the maftpro tells the ECU it's getting across the entire range. If you double this number, the ECU will think that twice the amount of air is coming in than before. When you add bigger injectors to this mix and leave everything as-is, the ECU is going to make the injectors fire for the same duration as before, but you're going to get far more fuel dumped in. Going from 440's to 870's, you'd get pretty much double (870/440=1.97) the fuel going in.

    Therefore, you need to tell the engine that it's getting about half the amount of air that it really is, so it fires the injectors for only half the time it otherwise would and you get back to a normal fuel mixture.

    Try searching for threads that include 'maftpro', 'injectors', and 'mainscale', and you'll get a lot more info on this exact topic. Lots and lots of people go from 440's to 550's or 680's, and have to back off their mainscale to accommodate.
    1989 Navy Blue Turbo BPU+

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    Default Re: speed density mode questions

    Quote Originally Posted by JimR View Post
    It will not be able to auto-adjust enough. If you want to run 14.7, I suggest you turn off all Part Throttle Tracking and let the 7M ECU do it's job. It is very good, and very stubborn and persistent about maintaining that ratio, lol. :-) You must have a narrowband O2 sensor still installed for this to work.

    Main scale works by adjusting the overall amount of air that the maftpro tells the ECU it's getting across the entire range. If you double this number, the ECU will think that twice the amount of air is coming in than before. When you add bigger injectors to this mix and leave everything as-is, the ECU is going to make the injectors fire for the same duration as before, but you're going to get far more fuel dumped in. Going from 440's to 870's, you'd get pretty much double (870/440=1.97) the fuel going in.

    Therefore, you need to tell the engine that it's getting about half the amount of air that it really is, so it fires the injectors for only half the time it otherwise would and you get back to a normal fuel mixture.

    Try searching for threads that include 'maftpro', 'injectors', and 'mainscale', and you'll get a lot more info on this exact topic. Lots and lots of people go from 440's to 550's or 680's, and have to back off their mainscale to accommodate.
    I was told around -40 on the main scale. Mine is sitting at 0 is that normal? and I have a 2j swap with a piggyback so thats why I was asking. The 7m ecu fights with the maft pro from time to time. I know 870's are a pretty big jump.

  4. #4
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    Default Re: speed density mode questions

    A mainscale of 0 simply means no adjustment. It always starts out like that.

    The nice thing about this change is that you don't have to guess or depend on other people's numbers. You simply do the math yourself and get the exact number you require. 0-(440/870)=-0.50 and -0.50*100=-50%

    After you make the change, take it easy cruising around the place and watch your vf number coming in to make sure the stock ecu is happy. There's a sticky about vf along with several threads in this subforum.
    1989 Navy Blue Turbo BPU+

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    Default Re: speed density mode questions

    Quote Originally Posted by JimR View Post
    A mainscale of 0 simply means no adjustment. It always starts out like that.

    The nice thing about this change is that you don't have to guess or depend on other people's numbers. You simply do the math yourself and get the exact number you require. 0-(440/870)=-0.50 and -0.50*100=-50%

    After you make the change, take it easy cruising around the place and watch your vf number coming in to make sure the stock ecu is happy. There's a sticky about vf along with several threads in this subforum.
    is the maft pro able to safely adjust for those injectors (870cc) or am I just wasting my time with them?

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    Default Re: speed density mode questions

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