Adjusting A/F ratio with MAF sensor?

[s10xtremist]

I read in this month's issue of Muscle Mustangs and Fast Fords magazine about a turbo kit they installed on a bone-stock '91 LX. The 5.0 HO put down 192 hp at the wheels. They installed the turbo kit and, at 9 psi, it made about 390 hp at the wheels. Anyway, they mentioned that they could adjust the idle mixture by rotating the MAF sensor in it's housing. Rotating it one way made the idle richer, rotating it the other way leaned it out. They said something like that with flow-through MAF sensors, changing the way the air hits the sensor will alter the mixture. Makes sense. Can we apply this idea to our trucks? Does changing the idle mixture affect the air/fuel ratio at other engine speeds, namely normal cruising RPM's?

[Old Man]

What a bunch of horsesh*t!!!

Yes rotating the MAF may allow some difference in how it reads the air entering, but what does that do? Nothing!!!Why?? Because the 02 sensors override everything to keep tune within the limits of what was programmed for air fuel mixture numbers. 02's have the final say and any changes in front of those readings are accounted for and adjusted to. Its how the computer adapts/learns for wear and whatever. If you could change the 02 reading numbers per air fuel mix, then it would stay there!

[Dimemaster]

Yes, it could work, but only until the computer relearned as Old Man stated above.

[Rob]

I believe at WOT the O2 sensors are not read and rely on the PCM programing, but I may be mistaken.

[Dimemaster]

The MAF adjustment was for idle mixture, not WOT. MAF doesn't do didly at WOP, it's all on the O2 sensors.

[Injected]

What's up S10xtremist? Good to see you here.

[Old Man]

I believe at WOT the O2 sensors are not read and rely on the PCM programing, but I may be mistaken.

MAF is soley used for tuning WOT.

BUT!!!!!!!!


What it basis itself off, is the short term fuel trims.
See as you drive and things begin and continue to wear, in closed loop with all the sensors online the ECM learns and continues to learn and adjust. Then this learning becomes locked in long term fuel trims. WOT runs are then based off the adjustments of this. No matter what trick mod is done the ECM via the 02 sensors will adjust them to keep it within spec. Whatever is programmed to allow is all you can ever see unless your geeky enough, which I've never ever seen, you could remap new values with a good write program. The 02's are not deadly accurate and will allow a 14.2-15.2 range for the perfect mix. If you teach the ECM with like CAI kits, MAF mods and so fourth, you'll always be on the lean end of 14.7+. When the ECM goes into WOT it adjusts 2 points lower. So 14.7:1 ends up trying to tune 12.7:1 at WOT, but if you taught it lean ideals, then 15.2:1 ends up 13.2:1 WOT.

What you really want and no mod I've ever done skews readings to the rich side of what the ECM allows. Now that would be the ticket!!!


What gets my goat is now everyone always falls unto this, LETS SEE SOME NUMBERS. NUMBERS now mean more than they ever did, but really dont mean anything. Manufacturers list this dyno CRAP because we ask for it. We then buy after seeing this DYNO CRAP figuring we will get this gain. Well anytime you do something to the air flow you will indeed change the dyno readings. Leaner is meaner short term and always was. Leaner will show gains on the dyno, but once the ECM has commanded and entered the changes needed into the long term trims, does the gain stay???? Never!!!!! As and example, 3 of us did GMS model C MAF's and logged all the data we could. At first I saw lower readings (Lean) off data loggin sessions. Kossuth and one other saw 9 RWHP. COOL GREAT!! Leaner readings I got translated into 2 degrees of extra timing, COOL!! 6 months later I saw the computer learn most of it out, MAF to TPS had adapted, no longer getting performance MAF codes and also saw timing get pulled and put into long term trim values. It would light ping under loaded up hill WOT and bursts and the ECM learned timing retard which is never forgot! Kossuth redynoed his and found it lost 7 RWHP from were is sat before the GMS was installed.

I've learned that anything that SUGGESTS some kind of change/trick to ECM values cost you more in the long run!!! Only real tuning works!!

[Rob]

With my TunerCat software, I can tune the PCM to for a richer AFR. Stock it is set for 14.7, but I can increase or decrease that. I need some more time, and track time to mess around with it some more though.

[s10xtremist]

Howzitgoin, Injected?! I'm still here, kindasorta. I don't have a computer where I live now, so I just use my friend's when I'm here on the weekends. Good to see you're at the Planet, too. See you in the "Forced Induction" threads!

[s10xtremist]

Rob, I've been lookin into that Tunercat stuff. I was wondering if it is compatible with the F.A.S.T. reprogram I currently have with my S/C. In other words, would I have to draw up my own fuel/fire maps from stock or can I simply modify the program from the F.A.S.T. re-tune, since it already has the basic curves in it for boost? I need to richen it up a little under boost, but lean it out for normal cruising. Can it also modify rev/shift points? Mine won't upshift from 2nd or 3rd unless I back out of WOT ever so slightly. It's a little annoying for me.

[s10xtremist]

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