Maf Conversion Confusion, Please Help

Discussion in 'Fox 5.0 Mustang Tech' started by viper_dude_06, Oct 28, 2013.


  1. viper_dude_06

    viper_dude_06 Member

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    Hey everyone whats up? This isn't just another how to or why to convert to MAF thread...This ones a little different. Let me explain...

    I bought a 1987 Mustang GT a few years ago that is Speed Density. Well after doing some mods to it, Cam, Intake, Throttle Body, Head Work etc., everyone knows that the parts don't play nice with the EEC. The car runs with some power, but still not up to par.

    Ive been thinking about doing a MAF conversion to the car. While thinking of the conversion, and doing some research on what type of Harness I should get, as well as looking over the instructions on how to properly add a MAF Sensor and needed changes, I noticed that my car already has a stock Ford MAF Sensor installed along with the complete engine harness. Now my EEC is still a Speed Density DA1. Ive double checked and my car is a 1987 which wasn't equipped with anything for mass air. Ive also noticed that it has the notorious 8 pin female connector for the o2 harness instead of the 5 pin for '87. The actual o2 harness itself is still a 5 pin without the jumper wire that came in MAF '89 vehicles. Im supposing that one of the previous owners of the car had started to do a MAF Conversion and didn't finish it.

    Ok now that ive tried to give as much detail as I could with out writing a book, on to the question.

    In the Instructions for doing the conversion and installing the MAF meter, it says you need to add or change some of the 60 pin connectors around. Examples would be pins #9 and #50 need to be added. The thing is, that they are already running from the MAF Sensor to the those pins. All the pins in this link im posting up with this thread are already in their respective colors and places. Does that mean that I don't need to change any thing else around?

    Also the link doesn't say I need anything for the purple and yellow jumper wire on the o2 harness that came in the '89 MAF vehicles. But from what I understand, you don't need that jumper wire if your using your stock '87 harness, and if your just spicing in the MAF sensor. Im assuming that I either have a late '88 or '89 MAF harness though.

    Now for sure I know ive written a book...I guess the real question would be, can I just buy a A9L EEC and plug it in with out any worries and expect everything to start working? I know I have to do a few extra things like disconnect the MAP sensor vacuum hose. What im really concerned about is needing that Purple/Yellow jumper wire for the o2 harness, sense what im reading suggest that if its not wired up it wont read the o2 sensors, and if its wired up wrong, itll fry the EEC.

    I feel like its common sense and ive answered my own questions, but I guess im just looking for some reassurance from some of you good people that's been down this road already. Im just confused because I wasn't expecting any of the work to be done like having a harness already. Also I just don't know where to begin since im not the one who started this conversion. Thanks in advance for whatever advice you guys can give me.

    If there's anything else you guys need to know just ask. Im just lost on what I need to do to complete this process. Thanks again.

    Heres the link that im basing the 60 pin connector off of which happens to be on this site.
    http://www.stangnet.com/tech/maf/massairconversion.html

    Heres another link from eBay of a guy describing the differences between the Harness's for different years.
    http://www.ebay.com/gds/FOX-MUSTANG-SPEED-DENSITY-MASS-AIR-HARNESS-GUIDE-/10000000175794707/g.html
    #1
  2. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    O2 Sensor harness interchange and modification

    Originally Posted by 302EFI


    Revised 16-Oct-2011 to add O2 sensor harness warnings
    The wires for the 02's and low oil did not change throughout the years, they are all in the same place.
    The main ones you need to worry about are (on the harness end (ECU) that plugs into the 02 plug) is:
    \- 1. Lightblue / yellow
    - 2. White / Purple
    - 3. Purple / Yellow
    The White/Purple & Purple/Yellow gets looped for a automatic ECU
    The Purple/Yellow & Lightblue/Yellow for a manual ECU

    See http://forums.corral.net/forums/gen...manual-auto-differences-year-differences.html for more O2 sensor wiring harness info

    Basic premise to use with transmission swaps:
    Only run a 5 speed trans O2 harness with an A9L. Do not run an Auto O2 sensor harness with an A9L. Doing so will damage the computer’s internal signal ground.
    Only run an Auto trans O2 sensor harness with an A9P in a car that has an Auto trans. Using a 5 speed trans O2 sensor harness with an Auto trans will cause no crank problems.
    See http://www.stangnet.com/mustang-forums/749974-computer-issue.html#post7490537 for Joel5.0’s fix to the computer internal signal ground.

    90 model year harness only works with 90 model cars without inspection/rework.
    The 4 cylinder O2 harness uses 4 wire O2 sensors. It probably won’t work correctly without modifying it.
    #2
  3. liljoe07

    liljoe07 Active Member

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    To be correct this should read:
    Only run a 5 speed trans O2 harness with an A9L. Do not run an Auto O2 sensor harness with an A9L while using a Manual Transmission Setup. Doing so will damage the computer’s internal signal ground.

    This is incorrect. Start voltage is only sent to the 02 harness. It does not pass through it and then go to the Starter Relay or any other circuit that lets the vehicle crank. And the voltage is only sent because of the way the Auto Trans setups source its Neutral Sensing ground from the Starter Relay coil.
    #3
  4. viper_dude_06

    viper_dude_06 Member

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    That's some good info guys....thanks. My transmission is manual and that's why I was gonna go with the A9L EEC. My o2 sensor harness is from a 1987 so it only has the 5 wires...I guess that doesn't matter as long as I put the jumper on the harness to match the A9L Manual EEC. Which would be colors Purple/Yellow & Lightblue/Yellow. So if I do that can I just drop the EEC in the car and fire it up for the most part?
    #4
  5. Blown88GT

    Blown88GT Founding Member

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    There is nothing to change in the O2 harness. See attached instructions.

    Attached Files:

    #5
  6. viper_dude_06

    viper_dude_06 Member

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    I understand what your saying but my engine harness isn't from an '87 its from a late model '88 that came with the MAF connector already, plus an 8 pin o2 sensor form the factor. Maybe im just reading this wrong, but if I had an '87 harness, I wouldn't have to do anything to the o2 plug connector. All I would need to do is just follow the steps to install a MAF sensor connector and add/change a few pin on the EEC and id pretty much be good to go. But if I replace my harness with one from a '88 or '89, without replacing the o2 harness as well, then id have to create a jumper wire between (Purple/Yellow & Lightblue/Yellow) in the original o2 harness that came in my '87 GT to accommodate the new A9L EEC that ive installed right?

    Sorry about all this, Im just trying to get it all right the first time so I don't fry anything or burn any wires up.

    Heres a Quote from the a link.
    "IF YOUR GOING TO CONVERT TO MASS AIR MAKE SURE YOU CHANGE THE 02 HARNESS WITH THE ENGINE HARNESS AS WELL IF YOUR HARNESS UTILIZES 8 PINOUT 02 FEMALE PLUG. IF RUNNING THE 87 CONVERSION TO MASS AIR JUST LEAVE THE 02 HARNESS ALONE BECAUSE IT DOESNT MATTER."
    #6
  7. liljoe07

    liljoe07 Active Member

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    Correct, if you run a mass air engine harness, you must add the jumper wire to the SD 02 harness.
    #7
  8. viper_dude_06

    viper_dude_06 Member

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    Ok thanks. Like I said in my first post, I felt like I was answering my own questions. I really appreciate everyone's help. I know its not labeled an A9L, but could I go to Autozone and order an EEC for an '89 5 spd. They're only about a hundred bucks and come with a 1 year warranty. The site also says no further tuning required. I know I'll still need some, but I'll be able to drop it in and fire her up. Or is it best to go with an actual A9L? Sorry for all the questions.
    #8
  9. Blown88GT

    Blown88GT Founding Member

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    1. Only '88's with MAF connector were California cars because Calif. CARB required MAF
    [​IMG]
    2. AFAIK, '87 is identical to '88. The colors you state do not match the '88 drawing shown.
    3. All drawings are here: 1988 EVTM
    #9
  10. viper_dude_06

    viper_dude_06 Member

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    Ok now I'm really confused. I know for sure I dont have an '87 harness. I'm 100 percent sure of that. Maybe I have an '89 harness then. But like I said I know its not '87 because '87 doesn't have the MAF sensor connector. Its also a 4 pin MAF connector not 5 pin if that helps.
    #10
  11. liljoe07

    liljoe07 Active Member

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    If its a 4 pin, its from an 89. 88 mass air cars were 5 pin.
    #11
  12. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    If that is correct, I am wrong: it won't be the first time. If you notice that some of my posts have blue text stating Revised date DD-MMM-YYYY...information describing the revision. You'll see that I have made changes to reflect corrected information or new additions. BUT before I rewrite anything I would like to see a diagram of the wiring involved. Get out your scanner, colored pencils, Microsoft Paint, Microsoft Visio, Paint.Net or whatever you use to make diagrams and post it up. I'll give you credit for any drawings you create that are used in future posts.
    #12
  13. liljoe07

    liljoe07 Active Member

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    [​IMG]
    Dont have time for all that JR. But here is the simple version. The W/P on connector 31 goes to the Auto pin on connector 40. Then, the loop on the 02 harness connects Auto and NDS. Its only a circuit that provides a ground path for Pin 30 so the ECM can identify In Gear or In Neutral. Only reason it sees 12v is because the ground is sourced through the starter relay magnetic coil windings.

    So while 12v is sent to the 02 harness, it has no where to go but to the ECM for and Auto, or it dead ends if its a Manual Transmission setup. It in no way prevents a no crank situation.
    #13
  14. viper_dude_06

    viper_dude_06 Member

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    So its an '89 harness then....that's good to know. Also in my research I read somewhere on the net that it doesn't matter what transmission you use. Whether its Auto or Manual. What does matter is that you use the appropriate o2 harness to match the EEC that your using. If its an A9L then you need a manual harness, if its an A9P then you need an auto o2 harness. Its all about the EEC and o2 harness matching up dealing with the jumper wire in the o2 harness connector. Again the actual transmission itself doesn't really matter. So in my...I would just create that jumper to match that A9L computer I plan on using.
    #14
  15. liljoe07

    liljoe07 Active Member

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    And as far as the Auto 02 harness vs the A9l.

    Just plugging in the A9L into a Automatic Transmission setup will not damage the Signal Return. It cant because the way an Auto setup is configured, nothing connects PIN 30 to Signal Return in a Auto setup. If it was, and Auto ECM would burn up just the same.

    The Auto 02 harness is configured where it will send 12v to PIN 30 on crank. The issue is only and issue when you start hooking up the NSS Clutch Switch for Pin 30 and the NGS switch on the side of the T5. Thats what ties the start voltage and Signal Return together that gets you a damaged ECM. If you dont have either of those two hooked up, there is no way to fry an A9L with an Auto 02 harness.
    #15
  16. liljoe07

    liljoe07 Active Member

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    No, you need the correct 02 harness for the Trans you are using. An auto 02 harness with a fully functional t5 setup will fry the ECM. A Manual 02 harness with a Auto Trans setup will cause a code 67 to be logged, and the ECM will think the car is always in gear.

    Typically the two go hand in hand because most just use an A9L in 5 speeds, and A9P in Autos anyways. But using an A9P in a 5 speed setup with an Auto 02 harness can burn the ECM up just the same. Because you will still send 12v into the Signal Return, being that the Signal Return is a ground, you can guess what happens. Direct 12v to ground= burnt up ****.
    #16
  17. viper_dude_06

    viper_dude_06 Member

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    Ok I got you. So just to be safe about everything im just gonna use a manual trans, manual o2 harness, and A9L comp. Id prefer as less of a head ache as I can. Also in one of my earlier posts, can I just go to Autozone and buy a EEC from there for an '89?
    #17
  18. liljoe07

    liljoe07 Active Member

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    If they have them up in stock you can. Last I had seen, lots of places were out of stock. Amazon did have some though.
    #18
  19. viper_dude_06

    viper_dude_06 Member

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    Ok cool. Ill check it out whenever I get a chance
    #19
  20. Blown88GT

    Blown88GT Founding Member

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    Sorry, you're wrong. Look at my drawing for '88, there's only 4-pins on the MAF. Fox body used 4-pin MAFS '88-'93.
    #20

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