Tune after getting headers?
Melting Slicks
Joined: Feb 2007
Posts: 3,297
Likes: 398
From: Raleigh Suburbs
Okay, I misunderstood what you were trying to say.
Okay,what happens is when you have a perfect SD tune and then you also re-enable the MAF, what the computer does is it attempts to use the MAF as much as possible. When the engine is cold and until it gets up to the temperature where it will go into closed loop, it will use VE only. From there it uses the mass air flow except when there is a change in map, meaning there's been either a change in throttling or load. There is lag from when the computer realizes you are making a change until it swaps back to the ve table to figure out what it really wants to do. Unfortunately it already has the engine fueled incorrectly because it was attempting to use the MAF for that brief period until it saw that it needed ve to get a baseline number.
Map and RPM are absolute, so there is no lag and no guess work there. MAF takes time to give the computer an accurate reading and it really only works best when in a cruise situation where the throttle is constant.
Keep in mind the way the MAF actually works. They input a voltage/current to a wire and heat it up. They factor in the intake air temperature which may or may not be the truth at any given point anyway, and then they measure the resistance on that wire assuming that the air density can be calculated by how much temperature drop there is on that wire along with what was the temperature of the air causing that temperature drop/resistance. In other words, it's a hell of a mess anytime a change is taking place because it simply takes too long for that to heat up and cool down.
There are numerous tables that help to alleviate those problems but often times they are not tuned when people do a tune. It gets complicated for sure.
Okay,what happens is when you have a perfect SD tune and then you also re-enable the MAF, what the computer does is it attempts to use the MAF as much as possible. When the engine is cold and until it gets up to the temperature where it will go into closed loop, it will use VE only. From there it uses the mass air flow except when there is a change in map, meaning there's been either a change in throttling or load. There is lag from when the computer realizes you are making a change until it swaps back to the ve table to figure out what it really wants to do. Unfortunately it already has the engine fueled incorrectly because it was attempting to use the MAF for that brief period until it saw that it needed ve to get a baseline number.
Map and RPM are absolute, so there is no lag and no guess work there. MAF takes time to give the computer an accurate reading and it really only works best when in a cruise situation where the throttle is constant.
Keep in mind the way the MAF actually works. They input a voltage/current to a wire and heat it up. They factor in the intake air temperature which may or may not be the truth at any given point anyway, and then they measure the resistance on that wire assuming that the air density can be calculated by how much temperature drop there is on that wire along with what was the temperature of the air causing that temperature drop/resistance. In other words, it's a hell of a mess anytime a change is taking place because it simply takes too long for that to heat up and cool down.
There are numerous tables that help to alleviate those problems but often times they are not tuned when people do a tune. It gets complicated for sure.
Begs the question --> why even bother with the MAF sensor once VE is tuned, if it's really that inaccurate, makes little sense running it (which is where I concluded, on my setup - ran excellent).
The one problem I encountered was no MAF sensor triggers an error on the computer, thus will fail Computer Emissions. Unless something can be done running MAF'less.
I hear also it is recommended to run the MAF during inconsistent environmental conditions, however this could be just internet gossip, if really the MAF sensor is not even very accurate.
Team Owner
Joined: Jul 2012
Posts: 34,479
Likes: 532
From: Central PA. - - My AR15 identifies as a muzzleloader
I believe in the Beer Fairy
Thank you for elaborating on this. Looks like the VE table is NOT referenced 1st in this scenario, which is what I began theorizing.
Begs the question --> why even bother with the MAF sensor once VE is tuned, if it's really that inaccurate, makes little sense running it (which is where I concluded, on my setup - ran excellent).
The one problem I encountered was no MAF sensor triggers an error on the computer, thus will fail Computer Emissions. Unless something can be done running MAF'less.
I hear also it is recommended to run the MAF during inconsistent environmental conditions, however this could be just internet gossip, if really the MAF sensor is not even very accurate.
Begs the question --> why even bother with the MAF sensor once VE is tuned, if it's really that inaccurate, makes little sense running it (which is where I concluded, on my setup - ran excellent).
The one problem I encountered was no MAF sensor triggers an error on the computer, thus will fail Computer Emissions. Unless something can be done running MAF'less.
I hear also it is recommended to run the MAF during inconsistent environmental conditions, however this could be just internet gossip, if really the MAF sensor is not even very accurate.
Probably the most important mod you can do if you're going to run your MAF is to relocate the intake air temp sensor. GM put the IAT up where it heat soaks something terrible. My God it takes seven or eight minutes for that thing to return to the correct temperature after you've had it heat up when you shut the car off. I tuned a Suburban that way once and without exaggerating you had to drive almost 10 miles to get the IAT back down to ambient temperature. That was also a 2003 as I recall so still C5 era. Lq4 engine but still the same stupid IAT location. When that temperature is off by 40° you may as well wipe your *** with that MAF.
