Right, I'm sure there are plenty of folks who have pinging with removed screens but that doesn't mean removing the screens is what is causing the pinging. Some may confuse it for that, however.

I dug up the info I was discussing the other day...

"Increasing the airflow doesn't necessarily mean leaning the mixture. The PCM learns as it goes. It might be leaner to begin with when new mods are made but before long the mixture will most likely be right back where it was.

Actually, it's been my experience that suddenly increasing the airflow (like installing a lid or removing the filter) causes a richer mixture temporarily due to the PCM overcompensating initially. I can remove my filter and watch my WOT O2s go from .870mv to .930mv. Make another pass and watch them fall to .890. After another couple of passes they'll be back down to .870mv."

"Your PCM will adjust until it can maintain a stoic mixture (14.7:1) during closed loop operation (you are in open loop during WOT operation.) Wherever your WOT mixture (see, your WOT mixture is based on what the PCM has learned while in closed loop so indirectly PCM fuel cell changes do effect WOT operation) is once this is accomplished is where it's going to stay unless you change it with a MAFT or programming. So the answer to whether your fuel/air will adjust back normal is yes and no.

BTW, the PCM only has but so much range of adjustability. Once the Ltrims reach + or - %25 no more adjustment can be made. Autotap will tell you what your Ltrims are.

As I've said before, closed loop fuel/air should not be effected long term by airflow increasing mods so long as the fuel system is adequate since the PCM will make corrections to maintain stoic. WOT can be indirectly effected though. Just because the WOT is based off of the closed loop doesn't mean that the WOT will be corrected as accurately as the closed loop."

"How can a MAFT work when the B1 & B2 S1's are taking erronious readings? In other words, I don't see how you could possibly trick your ECM into running lean or rich for any extended length of time when the post combustion A/F will end up too rich or too lean. Why wouldn't the ECM just override the MAF?"

Very simple. The PCM is only learning when it is in closed loop operation. You're in open loop when at WOT. You have a base setting and a WOT setting on the MAFT. Once your base is set (meaning that you get your Ltrims where you want them) you can make adjustment to the WOT mixture. These adjustments have WILL NOT be learned out by the PCM since they will only be affecting the mixture at WOT when the PCM is NOT learning."

"There are TWO adjustments on the MAFT. One is called the base setting and one is called the WOT setting. The base setting is used to bring the Ltrims close to zero. Some people like 'em a little on the positive side. Some people like 'em a little on the negative side for different reasons. The point is to get them fairly close to zero to give the PCM a good place at which to start.

Scenario...

You've just changed from 26.4 lb injectors to 30 lb injectors. You drive it around awhile to let your PCM learn. Let's say the Ltrims were zero before the injector change. Now your Ltrims are negative (probably about %14 negative since the new injectors flow about %14 more than the old ones) indicating that the PCM has pulled some fuel in order to get the idle and part throttle (CLOSED LOOP) back to a mixture of 14.7:1 which is a theorectical .450mv as read by your O2 sensors (in actuality you will notice that your O2 readings switch back and forth from lower than .450mv to higher than .450mv over and over but the average is about .450mv during closed loop operation.) Let's say that your WOT O2 readings were about .870mv before the larger injectors. What will they read now? You guessed it. They're reading higher than .870mv. Maybe .950mv or so. This is too rich for best power. The closed loop mixture adjusted back to where it was supposed to so why didn't the WOT O2 readings adjust back to .870mv? [READ THIS PART CAREFULLY] Because the WOT fuel cells (again, WOT is ALWAYS open loop meaning that the O2 sensors are NOT being read by the PCM) is an approximation that is merely based, and I'd say rather loosely, on what the PCM learns during closed loop. This relationship between open loop and closed loop is NOT a 1:1 ratio. When the PCM subtracts %15 from the closed loop fuel cells it doesn't subtract %15 from the WOT fuel cells. I don't know how much it does subtract but it is nowhere close to %15. Well why is that? You'd have to ask GM why they programmed it that way. It works fine when the engine is stock and that's all they really cared about.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Colonel:
[QB] Wait a minute. You're getting into porting the MAF now. That's a TOTALLY different story as you're altering the reported load to the PCM which is not the case with descreening (and also why your fuel/air is not affected.)</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">How is this different though? The MAF does not report LOAD to the PCM. If I'm not mistaken the MAP sensor is used to help determine engine LOAD. IMHO Porting your Maf is simply the next radical step after Descreening it. Both physically doing the same thing which is getting more air into the Engine than the MAF can account for. Why only now does your PCM stop learning about this lean condition and correct the problem with a LongTerm Fuel change?

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">
And no, I've not seen where people have caused pinging problems by descreening (porting, yes.) Speak up if you're out there. It's been over 4 years into this game and I haven't heard from you yet. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> </font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Wow! Really? Before I even got my LS1 it was common knowledge that Descreening the MAF was an attempt to lean out the A/F Ratio and that some cars respond better to it and others don't.

 

Stealthstalker:

I believe the reason porting is different than descreening is that the MAF electronics, through a temperature reading, measure the velocity of incoming air to determine load.
Porting the MAF housing causes the velocity of incoming air to slow, even if more air is coming in. The computer will think less air is coming in and pull fuel and/or add timing, possibly causing pinging/KR/detonation. This is how a ported MAF causes a lean condition, unless it is recalibrated. If it were just more air coming in, the system could adjust, at least within stock parameters.

I sympathize with you in that I don't like to risk messing with a MAF sensor at all, even descreening it. The electronics are sensitive, and I worry more about a dead bug condition than a lean condition. However, the Colonel is right in that descreening has nowhere near the impact of porting. Descreening should only impede airflow less. <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" />

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by StealthStalkerLS1:
<strong> The MAF does not report LOAD to the PCM</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Not true. The PCM determines line pressure in auto trannies from info received from the MAF. This is where porting the MAF becomes a problem.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Colonel:
[QB] Right, I'm sure there are plenty of folks who have pinging with removed screens but that doesn't mean removing the screens is what is causing the pinging. Some may confuse it for that, however.</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I certainly wish someone could explain then, why after I removed my Screen.. Weeks after the PCM should have learned and made changes to the Fuel Maps that I still got bad Pinging.

After I put the home-made screen it. WOW!.. Suddenly all that pinging IS GONE!.

Thanks for digging up that info.. It's a lot to soak in.. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

SSLink,

Thanks for explaining the Ported vs. Descreened. I'm still learning a lot about this stuff so I apologize if I'm starting to sound like I'm aruging with you guys for the sake of aruging. I'm not.. Just trying to question some of this stuff that makes no sense to me..

camaro_ls1,

Thanks for the correction..

<img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Gary Z:
<strong> Colonel, Brian,

This is the most interesting and informative discussion that I have yet discovered on this valuable site. Thanks to both of you for your efforts.

The lesson for the rest of us should be that one of the best ways to learn is to ask questions that will get the experts into a pissing contest. <img border="0" alt="[punch]" title="" src="graemlins/gr_punch.gif" />

-Gary </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Hey no problem but I'm hardly an expert in this regard.. I've got a lot to learn!

<img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

 

Slow down Stealth. You're just a little confused. I'll see if I can help you out.

The MAF sensor reports a signal to the PCM. The PCM translates this signal into a load (maybe I should call this a flow rate to be less confusing.) You can read this calculation in Autotap under "MAF Air Flow Rate." Increase the air coming through the MAF and this number goes up. If the number goes up, more fuel goes in. You can also read the actual signal that the MAF is sending to the PCM. I think it's under "MAF signal."

I see SSLink has started explaining the difference between porting and descreening before I'm able to get through with this post but I'll elaborate a bit.

The signal that the MAF reports to the PCM is based off of resistance (cooler wire has less resistance) and velocity. When you port the MAF you slow the velocity (same amount of air moving through a larger oriface.) It's a common misconception that the mixture is leaned due to more air entering the engine. While in theory, a tiny bit more air may enter the engine, the real reason is that the reported load from the MAF to the PCM is lowered due to the afformentioned lower air velocity throught the MAF.

Now, remove the screen. Did the velocity across the MAF wires decrease? No. Why? Because the oriface is still the same size.

"Wow! Really? Before I even got my LS1 it was common knowledge that Descreening the MAF was an attempt to lean out the A/F Ratio and that some cars respond better to it and others don't."

If that was common knowledge (which it's not in informed circles such as LS1Tech) then it was common misknowledge, if there is such a word. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> I think you're associating descreening and porting too much. They are physically and effecively two completely different things. The effects of which have nothing to do with one another in priciple nor in actuality. One is not simply a more radical version of the other.

 

Hey StealthStalkerLS1,

I don't think anyone's taking your comments as "arguing". We're all just discussing. Each LS1 behaves quite differently, that's been established. You know you're car. That's the most important part. Whatever stopped your pinging, stick with it!

 

Just one last thought. Air being forced through the openings in a screen could be moving at a slightly higher velocity than the same amount of air flowing through an open orifice, although I have no proof of this (any physics majors out there?). Although the speed of the airflow should have time to adjust by the time it reaches the sensor electronics,there could be a slight difference which the PCM could misinterpret. If you're just on the edge of running lean before descreening, I suppose this could theoretically put you over the top. Just a real hypothetical $.02. Sorry to waste everyone's time... <img border="0" alt="[barf]" title="" src="graemlins/gr_barf.gif" />

 

sorry for jumping into this but, isnt the whole point of fuel injection to be able to constantly adjust the air/fuel ratio?

if the car can handle the big airflow changes from an exhaust or an intake, then why wouldnt it be able to handle the little airflow increase from taking the screen out?

my truck has been descreened for a long time, and i am about to go outside and take the screen off of my moms SS

 

Silverado:

Again, the problem isn't increased airflow, it's
screwing up the MAF sensor's ability to measure it accurately, and fooling the PCM. See the Colonel's last post above.

Frankly, I think that removing the screen should either do nothing or help 99 percent of the time.
In my last post I was just speculating why a few
folks could get pinging from descreening. <img border="0" alt="[bomb]" title="" src="graemlins/gr_bomb.gif" />

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Colonel:
The MAF sensor reports a signal to the PCM. The PCM translates this signal into a load (maybe I should call this a flow rate to be less confusing.) You can read this calculation in Autotap under "MAF Air Flow Rate." Increase the air coming through the MAF and this number goes up. If the number goes up, more fuel goes in. You can also read the actual signal that the MAF is sending to the PCM. I think it's under "MAF signal."</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Gotcha! that makes sense.. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Colonel:
I see SSLink has started explaining the difference between porting and descreening before I'm able to get through with this post but I'll elaborate a bit.

The signal that the MAF reports to the PCM is based off of resistance (cooler wire has less resistance) and velocity. When you port the MAF you slow the velocity (same amount of air moving through a larger oriface.) It's a common misconception that the mixture is leaned due to more air entering the engine. While in theory, a tiny bit more air may enter the engine, the real reason is that the reported load from the MAF to the PCM is lowered due to the afformentioned lower air velocity throught the MAF.

Now, remove the screen. Did the velocity across the MAF wires decrease? No. Why? Because the oriface is still the same size.</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I see.. So removing the screen really only increases airflow but not volume. I just assumed because the airflow thru the MAF was no longer Unform across the entire surface area of the MAF (in part by the MAFSCREEN itself) that the sampling wires were letting some amount of air thru unaccounted for. AFAIK the whole purpose of the screen is not to slow down airflow but to increase accuracy of the air entering the engine.

I'm still not sure why the MAF won't need to be recalibrated for the higher airflow though?

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Colonel:
"Wow! Really? Before I even got my LS1 it was common knowledge that Descreening the MAF was an attempt to lean out the A/F Ratio and that some cars respond better to it and others don't."

If that was common knowledge (which it's not in informed circles such as LS1Tech) then it was common misknowledge, if there is such a word. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> I think you're associating descreening and porting too much. They are physically and effecively two completely different things. The effects of which have nothing to do with one another in priciple nor in actuality. One is not simply a more radical version of the other. [/QB]</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Nodding: Yes, perhaps your right. I admit I thought descreening and porting were basically two versions of the same thing. I now realize thanks to your help and everyone elses that it's in fact two different things..

<img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by camaro_ls1:
<strong> Hey StealthStalkerLS1,

I don't think anyone's taking your comments as "arguing". We're all just discussing. Each LS1 behaves quite differently, that's been established. You know you're car. That's the most important part. Whatever stopped your pinging, stick with it! </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Thanks Camaro_LS1! I'll definitely continue to learn more about this subject and stick with what works.. that's for sure!. FWIW my Short Term Fuel Trim Data was always 0 when I last autotaped my car so I'm hoping that means I'm neither Lean nor rich or that my LTFT's have already made the correction. Ghetto Maf screen is working!. haha..

<img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

 

Man.....do we get this knowledge for free <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" /> <img border="0" title="" alt="[Cool]" src="gr_images/icons/cool.gif" />

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Lastyrss:
<strong> Man.....do we get this knowledge for free <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" /> <img border="0" title="" alt="[Cool]" src="gr_images/icons/cool.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">No, please make out all checks payable to:

Camaro_ls1
12345 Walkyourass Dr.
Dearborn, MI

<img border="0" alt="[jester]" title="" src="graemlins/gr_jest.gif" />

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by SSLink:
<strong> Just one last thought. Air being forced through the openings in a screen could be moving at a slightly higher velocity than the same amount of air flowing through an open orifice, although I have no proof of this (any physics majors out there?). Although the speed of the airflow should have time to adjust by the time it reaches the sensor electronics,there could be a slight difference which the PCM could misinterpret. If you're just on the edge of running lean before descreening, I suppose this could theoretically put you over the top. Just a real hypothetical $.02. Sorry to waste everyone's time... <img border="0" alt="[barf]" title="" src="graemlins/gr_barf.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">You'd think some sort of MAF Calibration would be in order..

 

Wow too much input! So from what I gather from all this. To put it as simple as possible.
Descreening the MAF is a good thing.
Porting can be a bad thing.
So going through all this would I be ok if I purchased something like the Granetelli MAF which is recalibrated, or something like the zo6 conversion MAF, or is it a waste and I should just descreen my MAF and leave it at that?

 

zTrackerz:

I think you've got the "jist" of it. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

If ya really wanna know, your stock MAF sensor flows enough air to make well over 400 rwhp.

Just descreen it, or even leave it alone. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

The only reason I have an aftermarket MAF sensor is that I f....d up my stocker messn' with it. <img border="0" alt="[bang head]" title="" src="graemlins/gr_banghead.gif" />

If you want to lean your a/f, it's much more accurate and less chancey to do it with a MAF translator or programming. My last $.02. <img border="0" alt="[driving]" title="" src="graemlins/gr_driving3.gif" />

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by zTrackerz:
<strong> Wow too much input! So from what I gather from all this. To put it as simple as possible.
Descreening the MAF is a good thing.
Porting can be a bad thing.
So going through all this would I be ok if I purchased something like the Granetelli MAF which is recalibrated, or something like the zo6 conversion MAF, or is it a waste and I should just descreen my MAF and leave it at that? </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">In summary, do descreen your MAF. Don't port it. There is an exception though. Some M6's respond well to MAF ends tuned with a MAFT. Not sure if you have a manual or not. IMO, don't waste your money on a GMAF. There are guys here with BIG rwhp using the stock MAF.

 

While a lot of this maybe true for m6's, i removed my screen on a bone stock '02 WS6 A4.
With the screen out, the car shifted alot softer between gears. With the screen put back in it shifted fine. When the screen is removed in A4's it reports less load therefore the PCM commands less line pressure to the tranny. Trust me i confirmed this 3 times in a row. So in A4's descreening does have something to do with line pressure. So if you guys are thniking of descreening your MAF in your A4's have the line pressure bump about 8% to 10 % to firm the shifts back up so your tranny isn't slipping too much. This is what i have noticed on my stock 2002 WS6 A4.