I keep hearing people say that it does not matter if you get your engine perfect with the MAFT, cause the PCM is going to change it anyway.


Why in the hell would the PCM change something that is near perfect. For example..When the MAFT is used to program the engine for optimal A/F.

I thought it only made changes if there was a lean or rich condition? It always tries to acheive the perfect balance by reading the O2 sensors and the LTFT's.

If the MAFT had the PCM seeing everything perfect then please explain why the PCM would screw it up?

This idea seems to go against the grain of original reason the PCM learns in the 1st place. :confused:


[Modified by chuckster, 8:31 AM 8/13/2001]

 

I know that the PCM can't "learn away" changes to the MAF, at least entirely. I put a GMS MAF on my car and it lost 15-20 lb/ft of torque over the entire range under about 4500 RPM. If the PCM could just learn out the change, you would think that power would improve over time as the computer figured out what was going on. That didn't happen in my case. The power curve stayed lower with the GMS MAF in and returned to normal as soon as I put the stocker back in. I gave the car plenty of time to learn between tests too. So at least from my tests, you *can* make changes to the MAF and make them "stick".

Mike

 

I have been told that the PCM will relearn out any changes you make to your BASE settings with the MAFT.

The MAFT just basically tricks the PCM into seeing less or more air so that it compensates with less or more fuel. The logic is that the PCM can monitor the 02 sensor readings at part throttle. It knows what the 02 readings should look like for the amount of fuel it is dumping in. If the 02 readings are not in the range it is expecting, then it will make adjustments and use the Fuel Trims to adjust it to what they should be, thus eliminating the changes you made with the BASE settings on the MAFT.

Because of the way the PCM operates at WOT, the WOT settings on the MAFT are not learned out. The PCM pays no attention to 02 readings at WOT and therefore takes the reading of the MAF (along with a few other sensors) and looks up in a table how much fuel it should be injecting.

It was explained to me like this by a very reliable source that is extremely knowledgable about the PCM in our cars.

However, I have seen cases where people's non-WOT autotap numbers do stay where you want them after the addition of a MAFT, and I have seen cases where these numbers went back to what they were before the addition of the MAFT.

I guess some of it is truly a mystery. There is debate after debate about this topic on ls1.com

 

Let me explain:

The PCM adjusts closed loop operation to 14.7 stociometric ratio (the chemically correct ratio where all fuel and air are used up). No matter what.

The PCM constantly adjusts the timing pulse to the injectors to modify fuel delivery by monitoring the O2 sensors feedback in closed loop mode.

If an immediate change from normal operation is required, the Short Term Fuel Trim is changed to normalize the A/F ratio. This would be seen as a skew on a scanner as + or - percentages of rich or lean adjustment.

If this short term adjustment happens long enough. The long term values are recalibrated in the PCM memory, and the short term values are reset to 0. If the long term values hit a limit of about +/- 25%, and the short term values hit a limit of about +/- 25% a code is set indicating either rich or lean. How fast are long term values updated? It really varies a lot, and depends on too many factors to say for sure, but it could mean driving upwards of 250 miles to calibrate properly.

When you add a ported maf for instance, unmetered air gets by the elements in the MAF housing, and you create a lean condition. By doing this mod you trick the PCM into thinking there is a lesser load since you have decreased air velocity and increased air volume. So it increases timing, and reduces fuel delivery. BUT, the O2 sensors pick this lean condition up in closed loop mode, and tell the PCM to adjust the short term fuel trims to add more fuel. If this condition lasts long enough, (which it will if you dont remove the ported maf) it will update the long term fuel trims and reset the short term to 0 to normalize the system. The bennefit now, is added timing, and the ability to flow more air. The PCM has calibrated itself to the mod, but the mod is technically hacking the PCM for the bennefit to remain.

Now lets say the mod causes you to be too lean during WOT or KR occurs.

You add the MAF translator and fool the PCMs perceived load. You basically are telling the PCM there is a greater load, and it increases fuel delivery. The O2 sensors pick this up because they have allready told the PCM to adjust for the lean condition and the lterm values are set with the short term values at 0. Now the short term values have to adjust to 14.7. What your hoping to do, is not reduce the bennefit of timing advance by reducing KR or being too lean during WOT (open loop). You will still get the bennefit of extra air flow ability at high RPM.

What does all this mean?

The PCM normalizes, but you still get bennefits from the mods. ALso at WOT (open loop mode) the PCM heavily relys strictly on MAF, RPM, and TPS, to perform fuel delivery operations. It does not rely on O2 sensors, and freezes any fuel trim updates.

This is where the MAF Translator really shines as a tool to permanantly modify your PCM. It will techically permenatly skew your BASE (closed loop mode) aspect of the PCM. Of course the PCM will adjust to 14.7 no matter what in closed loop, but you have permently caused it to adjust fuel trims. The bennefits realized are timing manipulation, and slight WOT settings.

In WOT operation, the MAFT is permanent in every sense of the word. The PCM has frozen all possibilites of updating itself.

For more in depth reading. I did a write up on this very topic at
http://www.vetteguru.com




[Modified by kewlbrz, 1:23 PM 8/13/2001]

 

The readings that come from the MAF (with or without the MAFT) arrive before the fuel/air is burned while the O2 readings arrive after the combustion has taken place. The PCM uses the MAF readings (along with the fuel trims) to calculate the amount of fuel because this data is available immediately. The O2 readings are slower in coming and the PCM uses this data to adjust the fuel trims so that the MAF controlled readings will be more accurate the next time.

Imagine the moment after the throttle is opened; the airflow starts increasing and the engine needs more fuel. The reading from the MAF is available but the reading from the O2 sensors is from the combustion that took place before the throttle was opened. This is the reason that the fuel trims are used rather than just a direct reading from the O2 sensors.

The readings that come from the MAF are only correct if certain conditions exist in the airstream. If the pattern of airflow changes because of modifications to the intake stream then a correction to the MAF needs to be made so that it can correctly identify the amount of air passing through. This is the purpose of the MAFT. If the MAFT is set to report the correct amout of airflow to the PCM then the PCM and engine will be happy and healthy.

 

OK, your explination is good, and I think I understand it. (bear with me, I'm new to this) However, what's the story with people claiming a DECREASE in HP? How is that possible/beneficial?

A ported MAF will give you increased timing and air flow, correct? The disadvantage of this is that at WOT, you're not using the O2 sensors (open-loop mode) and the engine uses the baseline data- which will produce a lean mixture and there's no O2 sensors to correct this. So you add a MAFT which does the opposite- it modifies the baseline, giving you proper A/F at WOT. But wouldn't this counteract the ported MAF during closed-loop? Ie, the computer will no longer see a lean condition (since the MAF is now reported the correct numbers, albiet massaged a litle) and your timing will be back to where you started...

Again, bear with me... I'm new to this...

 

Remember you cant tune out the physical size of the ported MAF. If your engine needs the extra airflow in the upper RPMs it will now be able to flow it.

Also remember that lean "relativly" speaking isnt where you want to be. You want to be around 12.7 to 13.0 under WOT due to RPMs and the nature of a combustion engine to make peak power. This is actually enrichment from the stociometric ratio of 14.7:1 where you are 100% efficient. As the engine increases its pumping efficeincy with RPM etc... the chemically correct ratio changes.

In most cases after tuning everything with a MAFT youll end up with a little timing enhancement. There are other "better" tricks to still get timing, like adding larger injectors and using a MAFT to tell the engine you have a much smaller load. Or using air temp tricks on the IAT. Remember increases timing increases the chance of detonation. Its a juggling act to find the sweet spot after modding. But it does work and is effective.

Also PCM programming is the other route. BUt doesnt offer a tinkerer or constant modder the ability to tune as needed without sending off and waiting for new programming.


[Modified by kewlbrz, 3:21 PM 8/13/2001]

 

Once you find the sweet spot. Is it possible to give the Autotap/MAFT setting to a tuner to permanantly mod the PCM for those changes? For example. I have Powerloader. Could I send mine back to Steve Cole and get it progammed for the "Sweet Spot" and remove the MAFT?

If I wanted of course..

Also PCM programming is the other route. BUt doesnt offer a tinkerer or constant modder the ability to tune as needed without sending off and waiting for new programming.


[Modified by kewlbrz, 3:21 PM 8/13/2001][/QUOTE]

 

chuckster, yes that is possible, and is not uncommon at all. You will find that some of the biggest tuners out there, do this exact same thing.

Another aspect, is that once you have your PCM programmed, you can still use the translator on top of it.