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Originally Posted by BR3W CITY
Your tune will not be randomly setup to run without MAF. Speed Density tuning usually uses the custom OS in HP Tuners and isn't usually something a tuner would do without discussing (and charging) for.
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What years and ECMs are you referring to?
Any halfway modern ECM I've ever seen was already set up to handle no MAF. My 2007 LS7 was. My 2015 LS3 is.
In fact I know authoritatively that as far back as 1994, when they put a MAF on the LT1 for the first time, it supported speed density: I had a centrifugal blower and blew the discharge pipe off and it wouldn't run because the MAF was seeing full flow. So I unplugged the MAF and drove it home to fix the pipe... indicating it had speed density fallback mode as well.
In fact, now that I mention it, every single GM computer I've ever seen has speed density fallback.
I'm running it right now, in fact. The LS3 runs very well in speed density. Until I added the air straightener hex foils I was planning to keep it that way, but with the airflow fixed the MAF setup works well enough for me.
That doesn't mean -every- ECM does, but evey one I've experimented with, does. I also spoke with the guy in charge of GM crate engine calibrations and he confirmed it, and he told me that if it were up to him, all the crate motors would run speed density because it's near impossible for end users to set up a MAF pipe the same as the factory flow rates.
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so I unhooked the wire to the maf sensor and dam if it didn't go to running rite like its supposed too.
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And there you go, proof of my point. Pretty good guess, huh? :-)
What's happening is one of two things: there's a big enough intake/vacuum/air leak that air is making it into the motor without the MAF seeing it. So it goes way lean because it's not seeing all of the air, so doesn't add enough fuel. But it's gotta be a fairly big leak for that to happen.
The more likely cause is in the intake pipe. The pipe just has no hope of matching the flow characteristics of the stock pipe. So you can either "fix" your airflow, go to a longer tube with less bends, or continue to run without the MAF.
You can try those sections of pipe that have a MAF boss and honeycomb air straightener, which mostly solved my problem. Or you can run in speed density.
Long story short, your intake pipe is different than the stock pipe that was on whatever car that motor came out of, so the MAF location is not calibrated. GM tries to do their best by calibrating it for being in the middle of a straight pipe with 6" on either side of it, that's about the best they can do.