I have done some reading and i just don't understand this, yes i nop you max out the maf sensor under boost because the maf tables only go so high...so

-what happenes after tables are maxed
-is this a big deal
-should i port the maf sensor, this is a bad thing right???
-how do you tune after the maxed tables

I have not found a post that give a clear cut way to fix this.....or make it work with the tune..

 

The computer adds fuel based on the rising MAF reading as the engine consumes more air. Once it maxes out, it will add no more fuel to the engine, even though the engine continues to build more boost & flow more air. This causes the engine to go lean & potentially cause engine damage.

You need to see at which RPM the engine maxes the MAF table & then add fuel enrichment from there up to compensate for the added "unmeasured " airflow. Porting the MAF will decrease velocity through it & therefore give a lower air reading. This will lean the engine everywhere.

If you adjust the MAF table in the computer to richen it back up, you will be back at the same point maxing the MAF reading again.

You could fudge the injector size to get your enrichment back & then get a few more rpm (maybe 500 or so) before you max the MAF out or use the enrichment tables from idle up. If you max the MAF way before the peak engine RPM you will still need to use the fuel enrichment tables to add fuel up top. More than 1 way to do this & everyone has their preferences.

 

Hey Lonnie,

Frist thing thx for the info on the ATI bb balancer/hub (Great guy to pm or phone )thx...

ok i under stand that you will have to add fuel when you max out the maf sensor with what ever tables you wish, BUT i have seen what porting out maf sensor will do to the AFR on the dyno, it is all over the place 14.1-12.1 up and down how can you tune this?? unless this is just when you are N/A, We did i switch on the dyno with ported to none ported, the OE maf sensor gave us a perferct stright line on the AFR.....

If this is realy no big deal i can just tune when the maf sensor max's out...

What why have you done it on your car or other peoples cars....

 

It acts like a speed denstiy system when the MAF is maxed. Fuel will still be added based on RPM. You just need to add fuel in the PE tables above the rpm where the MAF maxes. Other tuning may also be needed depending on the combo. I have stock MAF and a stock computer and have no problem getting the desired AF ratio up to ~6,500rpm even though the MAF is maxed by ~4,000rpm.

Rich

 

So, the stock computer automatically goes into a speed density mode when it sees that the MAF has maxed out, and the RPMs continue to rise?

 

Well no. It's not speed density per se but it "acts like a speed density system" as I said. The PCM is still reading the MAF, but the MAF signal is no longer increasing as it is maxed out. The additional fueling is determined by the still increasing rpm.

Rich

 

It's too bad there isn't a FI specific MAF out there that wouldn't get maxed out (at least not in normal FI situation, if that's possible). It seem that would make tuning much easier. What is it about the stock MAF that limits it's capabilities?

 

Does the PCM even look at the MAF when it's in PE mode? I thought it just goes by the PE table.

 

I thought the maf was more for reference in closed loop not under wot when car go's into open loop.

Not sure why any of this matters I have seen more than one car making around 600 rwhp using stock computers with 57 high z injectors that drive like stock cars untill you put your foot into them.

John

 

Yes, it still reads the MAF in PE mode. It always reads the MAF, AFAIK.

Rich

 

Rich do you have your maf sensor ported.....and why

 

I have ported the housing and descreened it. I know this interferes with the units accuracy, but I don't care as I have tuned around this (inckuding some modifications to the MAF tables) to a quite satisfactory point. My goal was to decrease inlet restriction. When I get around to it, I will try the MAF on the outlet side of the SC to see if that has any beneficial effect. I suspect it will.

Rich

 

Rich - perhaps you can help me out here. I am working on my car, and currently planning to place the MAF between the turbo and the throttle body.

http://www.carcraft.com/techarticles/24549/

I believe that has a decent description of how the MAF system works.

The MAF sensor attempts to maintain a specific temperature in the hot wire setup. As a mass of air moves past that wire, it will change the temperature. On FI setups where it is on the pressure side, air inlet temps are either higher then stock, or near stock. As you are using a methanol setup (And I assume will be spraying after the MAF) that would mean your inlet temps are rather high compared to what the MAF was originally set for. This all can be corrected through a tune I believe...

The MAF will work on a pressurized side the same as it will before the inlet. The temps are different, the pressure is different, but the mass of air will still have the same effect, pressurized or not. It will need a tune, but the system still works the same way. (repeating for self-clarity)

When the maf is "maxed out" - is the maxing out a failure to maintain temperature (the sensor can no long calculate values that high)?

Or is it that the ECU simply can no longer accept how much it is saying. Like the sensor still works, but GM just cut the tables in the ECU at whatever point, figuring that it'd never need to go that high?

If it is a tables issue, then it can be done in the ECU and perhaps fixed. If it is in the MAF sensor AND the ECU, then both. I have seen too many threads that contradict each other on this, and figure you might know the truth behind it.

What precisely does the MAF send? I'm extremely curious, as you may remember I'd like to provide my my ECU with several fail-safe methods to protect the engine in the event of something going wrong and getting a boost spike. While I have some more down time till the car is done, I might as well try to figure something out...

 

I blew my motor, because I maxed out my MAF...

everytime it'd max out, my AFR would go to 15:1+

so, yes its a big issue...

 

Yes, but your car was not properly tuned. If it had been, it wouldn't have gone lean. Most blower cars max the MAF. You just need to add fuel in the rpm based PE tables to compensate.

More on the MAF later, got to get back to work

Rich