I read that with aftermarket CAI and ported/descreened MAF one should be able to add 20% to the MAF tables. So I decided to play with this (carefully) and see what happened. Well my air flow at idle went from 7 to 10 and 11 but my BLMs dropped from the low 120s to between 108 and 114. Is the car trying to adjust for additional air by dumping in more fuel? Thats scary rich. After a week of driving to/from work with the 120% MAF settings, I changed it back to stock and everything went back to normal.

Anyone else have experience with modifying the MAF tables?

 

BLM's less than 128 means the pcm is subtracting fuel because it thinks your a/f ratio is too rich. If your air flow numbers went up it seems like the pcm would try to add fuel to obtain the correct a/f ratio, but in your case the pcm was subtracting fuel. Anyone else have any insight on this?? So......it looks like you were running really lean for a while there (that's a bad thing) good that you set your tables back because your blm's looked a lot better before you changed the maf tables. Aftermarket maf's are supposed to be calibrated correctly so that you do not have to change your maf tables. On the other hand, if you have a modified stock maf (descreened, ported ends, etc) then you are most likely going to need to play with the maf tables because your blm's are probably going to be all out of whack. I'm dealing with this issue right now by the way. The previous owner of my car used ported maf ends and descreened the maf. My blm's are up around 155 at idle in closed loop in cell 16. I just bought a totally stock maf but havent placed it on my car yet, but hopefully this resolves the issue. I have a feeling that a lot of people who modify their stock maf's and claim that their car runs better this way have never actually hooked their car up to a scanner and looked at the blm's. A lot of them are probably running rich.

 

I'm going to change my sig by the way, it says granatelli maf but im not so sure it is. On my maf harness it doesnt say AC, like the stock maf i just purchased, so maybe it is a granatelli. Granatelli makes a generic aftermarket maf that's cheaper than their other units, but this unit is NOT calibrated for cai like their more expensive units. Even with their more expensive units you have to specify if you want them calibrated for cai. So maybe I have the cheaper one...who knows. All I know is it's coming off and I'll post my results w/ the stock maf once i get it on.

 

The fact is, your air flow at idle did NOT go from 7gps to 10gps. It didn't change one iota. All you did was miscalibrate the MAF sensor so it indicates that there is more air flowing. The PCM is seeing 50% more air flow (a "false" reading due to the miscalibration caused by descreening/porting and your generic alteration of the MAF calibration table). It adds 50% more fuel, to match the erroneous 50% more air. The O2 sensors see it is wayyyyyyyyy tooooooo rich, and the PCM cuts the BLM's back as far as it can to get the A/F ratio back where it belongs. It can't go any lower than 108, so since you have bottomed the BLM's out, at least on one side, (only a 15% fuel reduction, when you may need as much as 50%), it is probably still running pig rich at idle, fouling the plugs, washing the oil off the cylinder walls, etc.

You do not change air flow at idle by descreening or "porting" the MAF. If there is even a tiny reduction in pressure loss in the MAF.... resulting in a miniscule increase in air flow..... the IAC motor just twitches to reduce the total air flow back where it was - it only needs a certain amount of air to idle...... Altering your calibration table does not actually increase air flow at idle... it just screws up the meter reading, unless you have taken the time to properly develop a frequency vs. gps table for the "altered" MAF sensor.

 

Fred,

I understand my air flow did not actually increase, I was just reporting my FreeScan findings. I was under the impression that the stock MAF is calibrated for only so much air and by raising its values it would compensate for the different range. I was mistaken.

Thanks for the tech tips though. Can you offer any recommendations for optimizing the little things to help give my bolt-on LT1 a healthy stroke? I've added 1.5 degrees of timing across the board to where I'm only seeing a couple degrees of knock retard during shifts (headers, y-pipe, loudmouth...) and dropped the fan temps 4 degrees Celcius (lower caused probs). Kinda hard to test and tune in the middle of Miami...going to the track tonight for Midnight Madness and bringing the laptop along, will at least get some logs for later review.

 

Well, here is my experience:

I had stage II porting done as well as Hooker shorties and descreening of my MAF. I could tell I was running rich because of the gas smell.

So, finally I got DataMaster and TunerCat. Datamaster was telling me I was waaay rich..as you would assume my BLM's were in the low 110's across the board.

I reduced my MAF tables by 15% up to 20 and from there did a linear increase hitting stock at around 100 or so. Boom, so now I am on!

How I know I am on at all MAF readings? well, I disabled PE mode for a week and analyzed the data (as a side note, I found PE mode gives me about 15% more HP across the RPM range when used). Nice, I found, because I am now 126-130 across the board on my BLM's.

 

I also need a hand in this area.. At idle my ecm is set at 2.88gps, when checked with pc.comm.. I actually have 14 gps going through the sensor.. I too am running rich enough to kill all the skeeters in the neighborhood..my blms are around 128 and the car idles erratically once warm, Oh yeah, I am also running a d-1 charger.. Anyone know what tables to set the maf chart? Is this reading accurate? Or is my maf bad, no it has never been toyed with it's stock..

 

I used a 10% increase (110% of stock) on my gutted MAF, and when I found a set of cheap stock MAF ends I jumped on it, too many problems and no gains for this mod. I got lucky and found the ends only with no MAF to go with it.