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Thread: Safety of Open Loop MAF Only Tune?

  1. #1
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    Safety of Open Loop MAF Only Tune?

    Hey guys, I'm finally wrapping up my build (LS swapped 1985 Porsche 944) and now it's time to get my car to the exhaust fabricator.

    IMG_20181124_115256.jpg

    I'm not hell bent on this idea and will most likely end up towing it there but it made me wonder...

    Fresh LS1 build that came out of a 99 WS6. Mods below:

    -New 85mm MAF
    -LS6 intake and TB
    -42lb injectors
    -D585 coils (truck coils)
    -243 heads
    -TSP 224R .600/.600 114lsa
    -Custom 1 5/8" headers

    Things I've done to the tune:

    -Deleted/disabled all the typical stuff (VATS, EGR, AIR, TQ MGMT, etc.)
    -Updated injector data
    -Updated MAF data
    -Updated spark data for new coils
    -Upped idle setpoints

    I've started it up to check for leaks and bleed various systems and it purrs. Starts right up and idles extremely well. Now on the the bad news, I'm without o2 sensors as well as my wideband due to a lack of exhaust at the moment.

    With all that being said, if I disabled my fuel trims and forced an Open Loop/MAF only tune, would the MAF data that I updated be reliable enough to limp it to the fabricator and not blow up? When you guys tune your MAF's, are they usually off by much?

    Mostly thinking out loud here but I'd be interested to hear what you guys think!
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  2. #2
    Senior Tuner Ben Charles's Avatar
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    If it?s tuned correctly you?ll be fine

  3. #3
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    Quote Originally Posted by Ben Charles View Post
    If it's tuned correctly you'll be fine
    When you say "tuned" do you mean making sure I have the correct Airflow vs. Frequency values or actual values I derived from trims?

  4. #4
    Senior Tuner Ben Charles's Avatar
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    That would be the same thing... in closed loop trims correct fuel to stoich (if everything is correct)

    So if you click open loop it would run the same..
    Then you know you have correct fueling

  5. #5
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    Quote Originally Posted by Ben Charles View Post
    That would be the same thing... in closed loop trims correct fuel to stoich (if everything is correct)

    So if you click open loop it would run the same..
    Then you know you have correct fueling
    I think we have a misunderstanding. I've never had this engine running with this MAF (brand new) let alone recorded values from it.

    What I'm asking is, do you think a brand new 85mm MAF could vary enough from the 85mm MAF data tables floating around the web to cause harm?

  6. #6
    Senior Tuner kingtal0n's Avatar
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    you need a wideband. every car you build gets a wideband so you can watch the a/f ratio instead of having to guess. If it runs rich or lean, you can use the scanner to adjust the a/f ratio so you can drive it anyways. just t o get from point A to B its simple.

    I always run my car open loop. Its never had a narrowband sensor. I also avoid the maf sensor because I use a turbo and maf sensors are very sensitive to airflow direction and any leaks.

    Engines like LS will run open well anywhere from 12:1 to 17:1, you won't even notice barely any difference at part and low throttle. The rich 12's 13's will foul plugs. the lean 15-17's are usually fine for cruise and light load. I tune my engines open loop target 15.2~ but some have said 16's and even 17's are used with success. You won't be able to tell without the WB O2 though.

  7. #7
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    You need to check your engine with a wideband before driving it.

  8. #8
    Do your custom headers have an O2 bung? You could put a wideband in there to start tuning. Only issue is you probably won't want to drive it around with open headers. Did that with my Mustang to drive to the exhaust shop. People didn't like it much.

    I would trailer the car to get exhaust and then tune it. Awesome project!

  9. #9
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    Quote Originally Posted by sixt9stang View Post
    Do your custom headers have an O2 bung? You could put a wideband in there to start tuning. Only issue is you probably won't want to drive it around with open headers. Did that with my Mustang to drive to the exhaust shop. People didn't like it much.

    I would trailer the car to get exhaust and then tune it. Awesome project!
    I really wish the headers had bungs. That would make this much easier but yeah, it's still incredibly loud. Sounds like Nascar in my garage!

    The trailer is schedule for tomorrow morning to take it to the exhaust shop. Then the real fun begins.

  10. #10
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    Then have the shop doing the exhaust add the bungs. It's done all the time

  11. #11
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    Quote Originally Posted by DrLoch View Post
    Then have the shop doing the exhaust add the bungs. It's done all the time
    I'm having them added just after the collector flanges. One on the driver side and two on the passenger to accommodate my AEM wideband.

  12. #12
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    Cause harm getting it started or cause harming running the piss out of it? Because those are very different things.

    It will be fine to start. It will need tuning work before running it hard.

    In my opinion anyways.
    Post a log and tune if you want help

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  13. #13
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    Quote Originally Posted by schpenxel View Post
    Cause harm getting it started or cause harming running the piss out of it? Because those are very different things.

    It will be fine to start. It will need tuning work before running it hard.

    In my opinion anyways.
    Definitely not running it hard. I was just talking about limping it to the shop.

  14. #14
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    Should be fine