A/F rich after SC install.

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  1. #1
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    Default A/F rich after SC install.

    Hoping someone can help out. How is AF determined after warmup? Is it just from the Fueling Table? The problem I'm having is that after installing the SC (same MAF same injectors) my A/F is richer than it was N/A. Also, turning on the A/C on sends the A/F richer too. According to my Fueling Table A/F should always be 1 below .40 load. I'm thinking something else is modifying the A/F, but I don't know what.
    Last edited by Bullitt5566; 05-16-2018 at 09:31 AM.

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  3. #2

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    Scott,

    The Ford EEC-V ECU using AMZ1/2 strategies, which you should be using if you are building a Cobra clone or derivative, will run in open loop prior to engine warm up, delivering whatever the tuner has programmed for an AFR but not referencing the O2 sensors for a closed loop calibration. Once the engine and the O2 sensors come up to temperature, the ECU goes into closed loop operation and uses o2 sensor feed back to maintain commanded AFR everywhere including idle. A tuner can override this in his tune and command open loop operation at all times. Unless your tuner has done this, your ECU should operate as I have described.

    I made the assumption you are using a Ford EEC-V ECU and Ford's OEM Cobra strategies. If you are using something else, like an aftermarket ECU, you need to contact the tech team at the ECU manufacturer and ask them how it behaves — although I would expect it would behave similarly.


    Ed

  4. #3
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    Thank you for the reply. It is so hard to find tuning information. You are correct, it is a EEC-V and I use SCT PRP. I recently removed the SC and sent it to Vortech for an upgrade. While the SC was removed I installed FRPP 60lb injectors and the stock MAF. N/A the tune was spot on. Awesome throttle response, A/F exactly where it should be. Perfect. Then I installed the S/C, first with a 90MM LMAF, and then the OEM 80MM MAF. Same setup as N/A except with the S/C thrown in. The engine stalls and feels sluggish after the S/C install. No other changes from N/A. The wideband says it is rich .90 AFR at idle. (I open loop at TP below 400 and RPM below 1100 due to the cam overlap) When I turn the air conditioning on it goes even richer. I've looked for air leaks after the S/C and there are none. Going on the assumption that with the SCT PRP, if you import the correct data files for injectors and MAF it will get the tune close. Any ideas why the S/C and A/C would cause the rich condition? BTW. I'm an idiot will data log the load to be sure it isn't ridiculously high this afternoon, I see no reason it would be.

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  6. #4

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    I am not sure about the S/C but turning on the A/C will cause the ECU to provide for more power to maintain correct idle.


    Ed

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    Ed, Again I really appreciate your help. Yesterday I adjusted the MAF transfer function to get it inline with the fueling table and it idles pretty good. I also went back and looked at the MTF in a previous tune done by a reputable tuner, and my adjustment matched his. I ended up multiplying the entire MTF by .80. I don't why the SCT provided MTF for a 90MM LMAF would be off by 20% but it looks like it was. I tried to adjust the injector slopes by 1.2 before adjusting the MTF and it didn't seem to have any effect. I thought it would have the same effect as scaling the MAF by .80 but it didn't seem like it did. So that has me concerned about the next step which is putting the Diablo MAF.ia in and scaling the injectors. I'm thinking about selling the 90mm LMAF and MAF.ia and buying a MAF with more range. I'm thinking SCT Big Air, but I'm looking for suggestions. Again thank you for your help.

  8. #6

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    I was going to steer you to a Pro-M 92 MAF but I forgot you are using a Vortech. I would still give the guys at Pro-M a call, explain what is happening and ask for their best thoughts. They do offer a number of blow through MAFs and all their MAFs come with flow sheets so you don't have to stumble around guessing. Here is their website => prom racing.com their phone is at the top right of the page.


    Ed

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    Thank you for the recommendation. Sorry so many questions. I have a 90mm LMAF and MAF extender. When I use the MAF extender I have to scale the injector slopes and displacement. If I buy a MAF with more range like the SCT BA3000 or Pro M, do I still scale the injectors and displacement?

  10. #8

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    You do Scott. Sadly, Ford built several hard stops into the EEC-V CPU strategies for things like maximum Mass Air Flow, injector size and so on .

    03Steve built an excellent tool to assist you in managing these sorts of things. I put it up in the TToC under the Tuning Section some time ago. The name of the post is Tuning Workbook Pro. It does the heavy lifting so you don't have to.


    Ed

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