Tim Sloper

Due to the descreened MAF the current MAF table is no longer accurate for your meter but I would probably just decrease the injector flow rate table a bit to bring the LTrims slightly negative (3-4%). Shifting or scaling the MAF tables blindly can create more problems than it helps especially since the transfer function is not linear. Once the LTrims are brought negative you can dial in the PE table. I see you are using your 02 voltages to guage your A/F ratio. Your target voltage range may or may not end up corresponding to the proper A/F ratio. Without a wideband sensor you will never know how close you are.

Tim

The Dragon

iTrader: (6)

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Tim Sloper:
<strong>Due to the descreened MAF the current MAF table is no longer accurate for your meter but I would probably just decrease the injector flow rate table a bit to bring the LTrims slightly negative (3-4%). Shifting or scaling the MAF tables blindly can create more problems than it helps especially since the transfer function is not linear. Once the LTrims are brought negative you can dial in the PE table. I see you are using your 02 voltages to guage your A/F ratio. Your target voltage range may or may not end up corresponding to the proper A/F ratio. Without a wideband sensor you will never know how close you are.

Tim</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">If I remember correctly, I decrease the injector table by multiplying by a # greater than 100%? Correct or no?

Thanks for the response and info!

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

Tim Sloper

To decrease the flow rate table you will want to use a number less than 100%. If you want to do a 3% drop you would enter 97% for example. Decreasing the flow rate table will cause the PCM to initially use a larger injector PW than it would have otherwise. At that point you will be delivering more fuel than is needed which will be reported by the O2 sensors. The PCM will then decrease the LTrims which will then drop the injector PW back to correct times.

Tim

The Dragon

iTrader: (6)

So far I've used the PE and have yielded 870-909 O2's at WOT but +5.1% part-throttle cruising Lterms <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />

Should I attempt the MAF instead??

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

<small>[ December 25, 2002, 12:50 PM: Message edited by: The Dragon ]</small>

The Dragon

iTrader: (6)

Thank You VERY MUCH!

The Dragon

iTrader: (6)

What happens if I've modified my Inj Flw table and still have +LTerms?

I made a 96% change and have 1.5 LTerms.
Previously it was +5.1.
<img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />

Doc99SShome

Multiply thru again by 98.0%,,,

BUT I would have elected to multiply the MAF table thru by 105.0%,,, and leave the injector table alone because it was correct in the first place and now you have lied to the PCM, which now has thrown several other things out of wack in your PCM.

You guys who muck around with the fuel injector table when it matchs the stock fuel system is totally unbelievable. If you modified the MAF sensor in any way, the MAF table is now off. The modified MAF will usuually under-report the actual amount of air going into the engine. You should have read the posts listed by John @ pace to understand this better.

Take the engineering approach to your problem, you will come out better.

Doc99SShome

You still dont understand the fine points here.

With the stock factory MAF, my ported factory MAF, and the GMAF, my timing at WOT has ALWAYS been 28 degrees.

What should it be?

What point are you trying to make?

Tim Sloper

If a stock MAF is modified in which its physical characteristics will result in inaccurate reporting relative to the 100% stock calibration then the MAF tables need to be adjusted accordingly. In practice people just scale the curve by some flat %... in theory this is not appropriate either. A modified MAF needs to be flowed against a stock version to construct a new transfer function that will report the same airflow under X conditions that the stock MAF did. A simple scaling is likely not to be totally accurate across the operating range of the MAF but it will get most situations by. In the case of a descreened MAF the variance from stock will be more a function of turbulence and intake tract response than that of the MAFs physical characterisics. Who knows when/if this variance will occur such that it will make a significant difference in the tune.

The bottom line is that if you are using a modified stock MAF the MAF tables theoretically need to be adjusted... its just knowing how much to correct accross the board.

In the descreened MAF scenario tweaking the injector table is harmless. Beyond that I would be correcting the transfer function as accurately as possible.

I am actually in the progress of getting this data on the more common aftermarket ends so I can tune with more accuracy right from the start. Its tough getting guys to go back to stock MAFs for some reason even when it really won't cost them anything in most setups.

Tim

NoGo

iTrader: (2)

My point is that both methods of adjusting LTerms will work.
However, adjusting LTerms using the MAF tables will cause side effects, some of which are in adverse to what we are all trying to do.... make more power.

Here a just a couple things you can do to your car by adjusting the MAF tables to reach the desired LTerms.

1) Loose Power. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> By increasing your MAF table to adjust Lterms you have just moved your timing table up in the g/cyl column. You now have less timing at part-throttle, and for 01 and 02 years less timing at WOT.

2) Destroy your Automatic Transmission. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> Shift pressure is determined by engine load. By moving the MAF table around you have just adjusted your engine load and shift pressure. You car will either shift like a banshee at low loads, shortening the life of your machine, or not shift firmly enough at high loads resulting is slippage and eventual failure.

3) Set SES codes, and make your car run like ****. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> By moving your MAF tables around, your MAF no longer passes the speed density test. You set an SES light, the MAF reading is ignored and your car runs like crap all the way back to your laptop.

4) Loose WOT fueling and even more power <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> . The MAF is not a linear function and cannot be adjusted by a block multiplication. By making block adjustments to the MAF to correct for LTerms down low you have just made your MAF more innaccurate up top which will have to be compensated for on your PE tables to get back to a proper WOT a/f ratio.

The MAF method is popular because it stems from MAFT tuning. Just because it is popular doesn't mean it is the smartest way to tune.

By telling people to make adjustments to their MAF tables, I think you are doing them a diservice, becauses they don't know what kind of other effects it will have on their engine, and they don't know that they will have to do to compensate for those effects.

Tim Sloper

NoGo,

I think there needs to be some differentiation here between situations...

I agree with what you just wrote in the case of someone trying to adjust LTrims when they are using a completely stock MAF or a modified MAF with a correct transfer table. The inj tables are the only right way to bring them negative.

If you have a modified MAF without a correct transfer table then the table needs to be corrected before jumping to the Inj tables otherwise you will exhibit the same problems you described above.

Tim

NoGo

iTrader: (2)

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Tim Sloper:
<strong> If a stock MAF is modified in which its physical characteristics will result in inaccurate reporting relative to the 100% stock calibration then the MAF tables need to be adjusted accordingly. In practice people just scale the curve by some flat %... in theory this is not appropriate either. A modified MAF needs to be flowed against a stock version to construct a new transfer function that will report the same airflow under X conditions that the stock MAF did. A simple scaling is likely not to be totally accurate across the operating range of the MAF but it will get most situations by. In the case of a descreened MAF the variance from stock will be more a function of turbulence and intake tract response than that of the MAFs physical characterisics. Who knows when/if this variance will occur such that it will make a significant difference in the tune.

The bottom line is that if you are using a modified stock MAF the MAF tables theoretically need to be adjusted... its just knowing how much to correct accross the board.

In the descreened MAF scenario tweaking the injector table is harmless. Beyond that I would be correcting the transfer function as accurately as possible.

I am actually in the progress of getting this data on the more common aftermarket ends so I can tune with more accuracy right from the start. Its tough getting guys to go back to stock MAFs for some reason even when it really won't cost them anything in most setups.

Tim </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I have a pre-calculated table that I apply to customers cars with ported MAF's to correct for their inaccuracy.

On a whole though, I always ask to go back to the stock MAF if it is available.

NoGo

iTrader: (2)

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

I think there needs to be some differentiation here between situations...

I agree with what you just wrote in the case of someone trying to adjust LTrims when they are using a completely stock MAF or a modified MAF with a correct transfer table. The inj tables are the only right way to bring them negative.

If you have a modified MAF without a correct transfer table then the table needs to be corrected before jumping to the Inj tables otherwise you will exhibit the same problems you described above.

Tim </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Yes, I agree.

I should have stipulated that. If you are using a modifed MAF, and making adjustments via Edit, then you need to go back to the stock MAF, or obtain a proper correction for your MAF first.

Doc99SShome

Tim,

Your point is well taken, the point about modifying the MAF table for the true frequency response of the MAF sensor. This will not be a simple multiplication of the entire table.

When I re-calibrated the MAF table for my ported, nylon ended factory MAF sensor, I went into each cell of the MAF table and made the appropriate changes. You need to use all of the fuel cell LTFT values as possible to guide you in how much each section of the MAF tables is to be changed.
BUT one needs to be very careful here and a smooth curve must always be the end result (and its a non-linear curve). If someone is working on the MAF table, they should check their mods by looking at the MAF table in the graphics viewing option.

When I installed the GMAF, I had to start all over. In fact, the final MAF table for the GMAF is closer to the stock MAF table than the ported MAF table is to the stock table. If tuners change other tables when the factory MAF has been modded or swapped out, they will run into drivibility issues that NoGo has described above, like, lower timing at WOT and lower power output.

The Dragon

iTrader: (6)

First off, I'd like to thank everyone here for the info. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> Invaluable.

Second: am I screwed if I don't go back to a factory MAF? What would be the procedure, and how difficult is it, to scale a ported MAF??
I can yank the factory one off of the wrecked WS6.

You guys are pretty <img border="0" title="" alt="[Cool]" src="gr_images/icons/cool.gif" />

Tim Sloper

The equation for the MAF transfer function is based off of King's Law. It is in the form of

frequency (flow) = a + b * flow ^ c

For a stock 98 MAF

a = -1552.817
b = 2381.265
c = 0.278

flow (frequency) = exp ((ln((frequency - a)/b))/c)

If you can get a fair number of data points you can use non-linear regression to find the above a,b,c values and then generate the rest of the MAF table from the new equation. It will save you alot of hassle from manually trying to estimate the new curve.

My advice to anyone would be keep your MAF completely stock if you have the ability to tune with something like LS1 Edit. It just isn't worth messing with the hassles a modified MAF brings along. If you do need a larger MAF for whatever reason go with a GM unit in which the MAF table is known (ie. Z06).

Tim

Doc99SShome

NoGo,

Talking about a disservice to your customers.
You go and change a table that is correct for the physical state, while not correcting a table that is incorrect for the physical state. How does that serve your customer?

At any load case you wish to discuss, at any point in time the engine will consume the same amount of air whether there is a GMAF, Pace MAF, ported MAF or stock MAF on board. You can not deny this, its the law of engine physics. However, each of these MAFs while they are ALL flowing the exact same amount of air, the outputted frequency is different. These MAFs are not incorrect, they are measuring devices which attempt to estimate the mass air density by outputting a frequency.

Now what do you need for each of these MAFs, you need a translator table which the PCM can look up and equate a given frequency with air flow. Each MAF mentioned above will have its own unique MAF table. The new GM MAF (I think it called the LS6 MAF), does it have its own MAF table? Is it adifferent table than the one we have for our LS1 cars? Well, yes it is different. This does not mean that the new GM MAF under reports or over reports the metered air, and its not in-correct. The new GM MAF has its unique flow characterics and therefore must have its own unique MAF (translator) table.

Now lets get back to the idea about the same amount of air going into the engine per each physical state (load Case). If the stock MAF sensor along with the stock MAF table does not creat shift problems for the A4s, then how could a different MAF with its calibrated MAF table which reports the exact same amount of air to the PCM cause shift problems and damage an auto tranny?????

NoGo, before you acuse someone else about disservice, you should examine what I have discussed above and see how what you are doing is serving your customers to the best of their interests.

LS1derfull

ON A HEADS/CAM car with good flow and a cam with 6800 rpm potential, dont underestimate the need to lessen pressure drop thru stock maf sensor as a way of making more power. These motors are healthy and they need all intake tract restrictions removed to make best power. I no this is off topic here slightly but i think its worth making adjustments to fueling to run modified maf.People who believe in hi velocity in intake tract are missing the boat, on this end of system anyway.

NoGo

iTrader: (2)

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Doc99SShome:
<strong> NoGo,

Talking about a disservice to your customers.
You go and change a table that is correct for the physical state, while not correcting a table that is incorrect for the physical state. How does that serve your customer?

At any load case you wish to discuss, at any point in time the engine will consume the same amount of air whether there is a GMAF, Pace MAF, ported MAF or stock MAF on board. You can not deny this, its the law of engine physics. However, each of these MAFs while they are ALL flowing the exact same amount of air, the outputted frequency is different. These MAFs are not incorrect, they are measuring devices which attempt to estimate the mass air density by outputting a frequency.

Now what do you need for each of these MAFs, you need a translator table which the PCM can look up and equate a given frequency with air flow. Each MAF mentioned above will have its own unique MAF table. The new GM MAF (I think it called the LS6 MAF), does it have its own MAF table? Is it adifferent table than the one we have for our LS1 cars? Well, yes it is different. This does not mean that the new GM MAF under reports or over reports the metered air, and its not in-correct. The new GM MAF has its unique flow characterics and therefore must have its own unique MAF (translator) table.

Now lets get back to the idea about the same amount of air going into the engine per each physical state (load Case). If the stock MAF sensor along with the stock MAF table does not creat shift problems for the A4s, then how could a different MAF with its calibrated MAF table which reports the exact same amount of air to the PCM cause shift problems and damage an auto tranny?????

NoGo, before you acuse someone else about disservice, you should examine what I have discussed above and see how what you are doing is serving your customers to the best of their interests. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I'll tell you what. I am going to take all of your very informative educational posts, and put them into a little binder next to my dyno computer and laptops. I am going to entitle it "Things to Remember". And before I do any more 750 HP cars, or any more supercharged cars, or any more turbo cars, I am going to go through that binder just so I can remember everything that you have told me and cherish it.

Thankyou for the book you have written above, it has changed my life.

keyboard warrior <img border="0" alt="[shoot]" title="" src="graemlins/gr_guns.gif" />

NoGo

iTrader: (2)

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by LS1derfull:
<strong> ON A HEADS/CAM car with good flow and a cam with 6800 rpm potential, dont underestimate the need to lessen pressure drop thru stock maf sensor as a way of making more power. These motors are healthy and they need all intake tract restrictions removed to make best power. I no this is off topic here slightly but i think its worth making adjustments to fueling to run modified maf.People who believe in hi velocity in intake tract are missing the boat, on this end of system anyway. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">On the very high horsepower applications removing the MAF is the best route.

For most power levels that you see on the street, modifying the MAF is going to do nothing but cause headaches.

If you are cranking out 500 HP on a solid roller, then, yes, I would be the first one to workover the MAF.