3800 what to do when you hit your MAFs ceiling

[Sinister Drag Designs]

realizing that anything over 22-23psi will outflow a LT1 or LQ4 what do you do to bring it under control. could you just use a AFC 2.2 to adjust from that point on

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[Mike K]

Bob, you then have to remap your fuel tables to scale it all down. It's going to be less accurate but it's really the only option that I'm aware of.

 

[03turbogt]

Originally posted by SINr247@Jul 25 2006, 06:59 PM
realizing that anything over 22-23psi will outflow a LT1 or LQ4 what do you do to bring it under control. could you just use a AFC 2.2 to adjust from that point on

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you give your old one to me so i can get my car running!

 

[Sinister Drag Designs]

i think ill hold on to it. ive been hearing using a AFC 2.2 beacuse the MAF it self is cant keep up with the flow. anyone heard of this method. also looking at scott cooks mod list,he uses a AFC 1.0 anyone know why or was that an old mod list?

 

[98 TGP TOY]

You are not outflowing the MAF, you are outflowing the MAF table in the PCM. The PCM table is only setup to read up to a 11,500 hertz signal. So once you flow enough air with your MAF that the signal goes above 11,500 then the PCM stops adding fuel and tops out.

Usually the AFC is used with modified MAF tables in the PCM. I think what is usually done, is you increase the mass air flow values at the top of the table. Then use the mini afc to scale the signal down. So if you look at the PCM tables the modification would look like this:

Stock
9000 - 300
10000 - 350
11000 - 400

Modified
9000 - 350
10000 - 400
11000 - 450

That way you computer thinks there is 450 grams of air going in when it reads 11,000 hertz. But your MAF is actually putting out a signal of 12,000 hertz, and you use the mini-afc to step the 12,000 down to 11,000. Since your PCM wont understand a signal of 12,000 hertz.

I have never done it, but I think thats how it works, roughly. Could someone confirm thats how you do it?

 

[xierxior]

theres a real simple fix to this problem just set pe to enable before you hit the maf celing then you can control your fueling with the pe tables and not worry about the maf.
this isn't the most accurate method but try working with a 255gram/sec maf on a 500hp motor and you'll feel my pain.

gtp toy has it as well you can use a mini-afc to scale the maf down but that's not accurate either.

 

[M@]

isn't this what the PowrTuner board is for?

It's been discussed many times at length over there from what I understand
There are several different ways to go about it.

MT

 

[Sinister Drag Designs]

vendors are still trying to mess with it. no one has nailed it yet. -

 

[Mike K]

Unless you're going to change the computer tables (I.E. how high the PCM can recognize a signal) then your only option really is to scale the MAF table down. Ron is a lot better versed on this than I am but I remember running into this same problem on the SHO.

 

[xierxior]

ODB-1 pcm's are fully cracked and theres several different versions with different tables added so I'm sure it can be done and the problem should actually be easier to fix on the gp pcms because it's a 16bit pcm right? ODB-1 is 8bit and theres some kind of mathmatical limit that prevents you from getting above 255gram/sec.
the pcm seems to rely on the MAF for trans line pressure and you'll really start to notice this is you fluff the MAF numbers like +20 percent the car will barely want to shift.
since other tables rely on the MAF table I don't think it's as simple as just added a few tables but it's definitly not impossible.

 

[BumpinGTP]

Originally posted by SINr247@Jul 27 2006, 05:45 PM
vendors are still trying to mess with it. no one has nailed it yet. -

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People have been running 20+ psi for years (myself included), I think we have it dialed in fairly well. A perfect example is Matt Meekhoff's drag car, 26+ psi on a stock L36 MAF. It is all about how you scale it.

 

[Sinister Drag Designs]

i was informed that it was an issue that was still trying to be resolved, but i guess you can say that about everything in our cars

 

[nitrous]

You are not outflowing the MAF, you are outflowing the MAF table in the PCM. The PCM table is only setup to read up to a 11,500 hertz signal. So once you flow enough air with your MAF that the signal goes above 11,500 then the PCM stops adding fuel and tops out.

Usually the AFC is used with modified MAF tables in the PCM. I think what is usually done, is you increase the mass air flow values at the top of the table. Then use the mini afc to scale the signal down. So if you look at the PCM tables the modification would look like this:

Stock
9000 - 300
10000 - 350
11000 - 400

Modified
9000 - 350
10000 - 400
11000 - 450

That way you computer thinks there is 450 grams of air going in when it reads 11,000 hertz. But your MAF is actually putting out a signal of 12,000 hertz, and you use the mini-afc to step the 12,000 down to 11,000. Since your PCM wont understand a signal of 12,000 hertz.

I have never done it, but I think thats how it works, roughly. Could someone confirm thats how you do it?

Yes, that is the generic concept of it, Mike. No one should ever need to change their MAF. I am running a 99MAF since it's a little better and doesn't need to be scaled as much as the earlier MAFs.

 

[xierxior]

I really don't see the big deal about maxing the MAF out anyways if you have a MAP sensor that can read the amount of boost you're running the computer will use your MAP/PE tables to control fuel. you'll have to tune your MAP table for the amount of boost you're running tho which is a little dangerous commanding 14:7.1 while in boost

 

[Mike K]

The problem is that the stock MAP sensor is only 2 bar so in Bob's case that's going to max out as well which means that he'll have to replace it with a 3 bar unit and then scale that as well. While doing that you may as well simply scale the MAF also.

Additionally, I wouldn't run a car on MAP alone. Too many variables aside from fueling are determined using the MAF. If you're going to run a setup you may as well not cut corners.

And that's my .02... :lol:

 

[Sinister Drag Designs]

actully the 2bar will hold up zoom used his up to 26-27psi. all about the tune i guess, he suggested sticking with the 2bar. i think he said that only cause he has not used one before