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Thread: Factory tune information

  1. #1
    Potential Tuner
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    Oct 2019
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    Factory tune information

    Afternoon guys and gals. I'm looking for information on how to work with an MVPI2 on a 2004 Chevrolet Trailblazer. I've got the 4200 Vortec with 300k miles; I know some folks wouldn't recommend messing with the tune on one with that many miles, but it's been reliable for the entire time I've owned it. The main issue I'm having with it right now is that it doesn't run right in certain weather conditions.

  2. #2
    What are your long and short term fuel trims? Typically a bit contrary as the ambient temp goes down? If so I?d be looking at intake gaskets, fairly common on those plastic plenums. If your fuel trims are both high in closed loop I?d start there. Also have you cleaned throttle body, and it needs done very well. When it?s dirty and doesn?t close far enough it causes vacuum signal issues with the map sensor due in part to the maps location. If you suspect intake is leaking best way to verify is with a smoke machine if ones available. Also perform a cam-crank relearn. Hopefully this is helpful

  3. #3
    Potential Tuner
    Join Date
    Oct 2019
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    Quote Originally Posted by badcoupe View Post
    What are your long and short term fuel trims? Typically a bit contrary as the ambient temp goes down? If so I?d be looking at intake gaskets, fairly common on those plastic plenums. If your fuel trims are both high in closed loop I?d start there. Also have you cleaned throttle body, and it needs done very well. When it?s dirty and doesn?t close far enough it causes vacuum signal issues with the map sensor due in part to the maps location. If you suspect intake is leaking best way to verify is with a smoke machine if ones available. Also perform a cam-crank relearn. Hopefully this is helpful
    Afternoon badcoupe. What it does is actually the opposite of what you said; it runs fine at ambient temperatures below about 65-70 degrees Fahrenheit, and idles high (around 1200 RPM) at startup above that. Once I get it out on the road, it seems to run fine. I'll try those things you mentioned, as well as changing a bad sensor that I know about, and see if that helps.

  4. #4
    Check your ltft and sftf that can lend you a lot of info. If they?re high ie; 9 or more it?s lean. If they?re the opposite, negative numbers it?s rich