Should I change the Maf Table or IFR?
Thread Starter
Staging Lane
Joined: Jan 2007
Posts: 96
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From: Michigan
Should I change the Maf Table or IFR? I was just wondering if I should change the maf table or scale down the ifr table to compensate for positive ltft's at idle. It's running pretty lean and it's just killing my eyes. The maf is stock but i have a k n, smooth bellows, and airlid. I have a 226/230 112+4 cam and ported heads which i'm sure is contributing to the problem. I know you aren't supposed to change the maf table if it is stock but I have the lid and k n before the maf leading me to believe that i should change that table. Any suggestions? Thanks in advance.
You should always leave your IFR table reflecting that of your hardware's characterisitics (If your injectors flow 28.8 lb/hr, that's what the IFR table should indicate)
As for not changing the MAF calibration just b/c it's stock, who told you that? Even if it hasn't been altered, don't you think the modifications you've done have altered the type of airflow that passes through the measuring plane? There's never a wrong time to tell your vehicle what kind of "true" airflow it is seeing. Equally the same is true for the VE. Now as to why you have lean trims at idle, that can be related to a number of things.
As for not changing the MAF calibration just b/c it's stock, who told you that? Even if it hasn't been altered, don't you think the modifications you've done have altered the type of airflow that passes through the measuring plane? There's never a wrong time to tell your vehicle what kind of "true" airflow it is seeing. Equally the same is true for the VE. Now as to why you have lean trims at idle, that can be related to a number of things.
Launching!
Joined: Jun 2006
Posts: 225
Likes: 9
From: Hudson Valley NY
Originally Posted by 00camarossMV
I was just wondering if I should change the maf table or scale down the ifr table to compensate for positive ltft's at idle. It's running pretty lean and it's just killing my eyes. The maf is stock but i have a k n, smooth bellows, and airlid. I have a 226/230 112+4 cam and ported heads which i'm sure is contributing to the problem. I know you aren't supposed to change the maf table if it is stock but I have the lid and k n before the maf leading me to believe that i should change that table. Any suggestions? Thanks in advance.
? the only reason I ask is if its exhaust fumes its running rich....................Paul 
The know it all's know it all
Joined: Oct 2006
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Originally Posted by 00camarossMV
I was just wondering if I should change the maf table or scale down the ifr table to compensate for positive ltft's at idle. It's running pretty lean and it's just killing my eyes. The maf is stock but i have a k n, smooth bellows, and airlid. I have a 226/230 112+4 cam and ported heads which i'm sure is contributing to the problem. I know you aren't supposed to change the maf table if it is stock but I have the lid and k n before the maf leading me to believe that i should change that table. Any suggestions? Thanks in advance.
turn off your fuel trim ( go open loop) add a bit of timming. Have you modified a factory screened MAF in any way ???????? If not leave that table alone and use the AFR vs Open loop vs collant temp table to square it up for AFR. Here is your freebie for the day. with that big a camshaft you will actaully want to idle the engine very lean as ( OBSERVED ) by the wideband 02.
Thread Starter
Staging Lane
Joined: Jan 2007
Posts: 96
Likes: 0
From: Michigan
I've noticed on this site a lot of people said that if your maf is stock leave the maf table alone, but nobody has said anything about a stock maf combined with an airlid ect.,or at least that i have seen. It makes sense to me to change the maf table I just want to confirm that's the right way. A lot of the people on this site say to scale the ifr to get the LTFT's down but then the same amount of people say to use the maf. The maf makes more sense cause i modified the airflow and i haven't changed the injectors to warrant an ifr change.
I know i'm running lean at idle because i hooked up an EGT machine to the exhaust and my afr was 16.5. And to DRIVER456, it's the exhaust fumes that are burning my eyes and making my clothes reek. If i'm not mistaken exhaust that burns the eyes means it's running too lean, is that right or no, it's just what i've heard on this site before.
Now, I have no idea why I have positive trims at idle, there are absolutely no exhaust leaks- fully welded, and no intake leaks before or after the maf so i'm pretty much clueless. The only things that i can think of is it's the cam's reversion or my o2's not reading properly because they're bosch and not the factory delco's.
Thanks for the replies and trying to help me out here guys.
I know i'm running lean at idle because i hooked up an EGT machine to the exhaust and my afr was 16.5. And to DRIVER456, it's the exhaust fumes that are burning my eyes and making my clothes reek. If i'm not mistaken exhaust that burns the eyes means it's running too lean, is that right or no, it's just what i've heard on this site before.
Now, I have no idea why I have positive trims at idle, there are absolutely no exhaust leaks- fully welded, and no intake leaks before or after the maf so i'm pretty much clueless. The only things that i can think of is it's the cam's reversion or my o2's not reading properly because they're bosch and not the factory delco's.
Thanks for the replies and trying to help me out here guys.
I belive one of the major tuning companies state to not change the maf, "It should only be changed if the MAF is modified from stock." I do not listen to this, and do adjust the airflow values to get the tune correct.
as for adjusting the AFR vs Open Loop vs Coolant temp table to get the fuel trims inline as the correct thing to do. While you can adjust this to get your startup in open loop to be commanding what is needed for best operation, it should have no effect on the fuel trims.
Ryan
as for adjusting the AFR vs Open Loop vs Coolant temp table to get the fuel trims inline as the correct thing to do. While you can adjust this to get your startup in open loop to be commanding what is needed for best operation, it should have no effect on the fuel trims.
Ryan
Thread Starter
Staging Lane
Joined: Jan 2007
Posts: 96
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From: Michigan
Originally Posted by Sean Collins
turn off your fuel trim ( go open loop) add a bit of timming. Have you modified a factory screened MAF in any way ???????? If not leave that table alone and use the AFR vs Open loop vs collant temp table to square it up for AFR. Here is your freebie for the day. with that big a camshaft you will actaully want to idle the engine very lean as ( OBSERVED ) by the wideband 02.
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The know it all's know it all
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Originally Posted by 00camarossMV
Hey Sean, my maf is totally stock but you said to turn off the fuel trims and use the AFR vs Open Loop vs coolant temp table to square it up for AFR? Is that table in LS1 Edit because i don't remember seeing that one. And I can't believe my cam is that big to where my afr has to be that high, there's got to be a way to get my afr to come down and my engine liking it.
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Staging Lane
Joined: Jan 2007
Posts: 96
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From: Michigan
I have the fuel air multiplier table, is that what you're talking about? just change it to 1.0000 in the idle area and pull a plug? what would be the point of that? and what do you mean by IVC- haven't heard that one before.
The know it all's know it all
Joined: Oct 2006
Posts: 500
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Originally Posted by 00camarossMV
I have the fuel air multiplier table, is that what you're talking about? just change it to 1.0000 in the idle area and pull a plug? what would be the point of that? and what do you mean by IVC- haven't heard that one before.
The MAF has very little to do with idle airflow value.
Air coming through the cam overlap can fool the
O2s and if this is messing the idle fuel trims around
it may also fool a wideband.
The extent to which open loop idle AFR mismatches
commanded is probably your VE table low end error.
Cam plays here (for the worse).
Cold and remote O2 sensors are another good way
to get crappy mixture control in closed loop. If the
wideband and narrowbands disagree then look to
bad feedback. Slowness makes for gross mixture
swings even if the average is right and this is what
can make it stanky even if it's centered.
Air coming through the cam overlap can fool the
O2s and if this is messing the idle fuel trims around
it may also fool a wideband.
The extent to which open loop idle AFR mismatches
commanded is probably your VE table low end error.
Cam plays here (for the worse).
Cold and remote O2 sensors are another good way
to get crappy mixture control in closed loop. If the
wideband and narrowbands disagree then look to
bad feedback. Slowness makes for gross mixture
swings even if the average is right and this is what
can make it stanky even if it's centered.
Last edited by jimmyblue; Jan 18, 2007 at 09:13 AM.
I tried both: MAF and IFR and honestly the IFR tune gives (me) the better result.
Between summer and winter I see a differerence of max +/- 2% LTFT. Tuning by the MAF table it wasn'tthat stable.
If you change the MAF table you also trick the G/Cyl value, which affects timing.
My IFR curve is not calculated by the injectors and fuel pressure, but by the LTFT/STFT. It's not a straight line but something like an "S".
For those that change the MAF table: how do you change the curve for high flow?
At that point it's in open loop. Wideband?
Between summer and winter I see a differerence of max +/- 2% LTFT. Tuning by the MAF table it wasn'tthat stable.
If you change the MAF table you also trick the G/Cyl value, which affects timing.
My IFR curve is not calculated by the injectors and fuel pressure, but by the LTFT/STFT. It's not a straight line but something like an "S".
For those that change the MAF table: how do you change the curve for high flow?
At that point it's in open loop. Wideband?
OK. Emissions 101.
The smell and what settles on your clothes is unburned, and partially burned hydrocarbons. They can be present in both lean and rich conditions. When its real bad its usually a rich condition. When you have a cam with a bunch of overlap you end up with unburned fuel, hydrocarbons, in the exhaust. REALLY bad for the cats. As everybody knows. If you were tuning with a 4 or 5 gas, you would tune the idle to maximize CO2, and minimize CO, and HCs Although the HCs are gonna stay pretty high. The more overlap, the more leftover O2 and HC. With very little overlap as in a factory motor, high idle vacuum, low overlap, the idle emissions would have very low levels of oxygen, and HC, and CO, and a high level of CO2.
Because of the high level of oxygen at idle with the bigger cams, a wideband sees it as lean. So you have to tune the idle "lean" as far as wideband readings.
Sean Collins has it right. Make the changes in the A/f correction. Or in the VE table. I've done some that have dips right where they idle. Set the PE to 0 to 1200 rpm.
The smell and what settles on your clothes is unburned, and partially burned hydrocarbons. They can be present in both lean and rich conditions. When its real bad its usually a rich condition. When you have a cam with a bunch of overlap you end up with unburned fuel, hydrocarbons, in the exhaust. REALLY bad for the cats. As everybody knows. If you were tuning with a 4 or 5 gas, you would tune the idle to maximize CO2, and minimize CO, and HCs Although the HCs are gonna stay pretty high. The more overlap, the more leftover O2 and HC. With very little overlap as in a factory motor, high idle vacuum, low overlap, the idle emissions would have very low levels of oxygen, and HC, and CO, and a high level of CO2.
Because of the high level of oxygen at idle with the bigger cams, a wideband sees it as lean. So you have to tune the idle "lean" as far as wideband readings.
Sean Collins has it right. Make the changes in the A/f correction. Or in the VE table. I've done some that have dips right where they idle. Set the PE to 0 to 1200 rpm.
Originally Posted by 00camarossMV
I've noticed on this site a lot of people said that if your maf is stock leave the maf table alone, but nobody has said anything about a stock maf combined with an airlid ect.,or at least that i have seen. It makes sense to me to change the maf table I just want to confirm that's the right way. A lot of the people on this site say to scale the ifr to get the LTFT's down but then the same amount of people say to use the maf. The maf makes more sense cause i modified the airflow and i haven't changed the injectors to warrant an ifr change.
I know i'm running lean at idle because i hooked up an EGT machine to the exhaust and my afr was 16.5. And to DRIVER456, it's the exhaust fumes that are burning my eyes and making my clothes reek. If i'm not mistaken exhaust that burns the eyes means it's running too lean, is that right or no, it's just what i've heard on this site before.
Now, I have no idea why I have positive trims at idle, there are absolutely no exhaust leaks- fully welded, and no intake leaks before or after the maf so i'm pretty much clueless. The only things that i can think of is it's the cam's reversion or my o2's not reading properly because they're bosch and not the factory delco's.
Thanks for the replies and trying to help me out here guys.
I know i'm running lean at idle because i hooked up an EGT machine to the exhaust and my afr was 16.5. And to DRIVER456, it's the exhaust fumes that are burning my eyes and making my clothes reek. If i'm not mistaken exhaust that burns the eyes means it's running too lean, is that right or no, it's just what i've heard on this site before.
Now, I have no idea why I have positive trims at idle, there are absolutely no exhaust leaks- fully welded, and no intake leaks before or after the maf so i'm pretty much clueless. The only things that i can think of is it's the cam's reversion or my o2's not reading properly because they're bosch and not the factory delco's.
Thanks for the replies and trying to help me out here guys.
*READ ME FIRST-- Tuning Docs,VE/MAF, SES Lights, FAQS!!!! + more! *05/06/06*
Here's some good info on the MAF and how it really works (as found within the sticky link above):
How the MAF really works
A great spreadsheet to help you get your injectors scaled correctly (from the same sticky):
Injector Scaling Calculations
The rest of the info in that sticky touches on everything from basic to advanced tuning concepts. While I wouldn't consider any of it to be the end-all be-all tuning guide, it does provide enough information to get your started and keep you pointed in the right direction.
yeah like txhorns said I try and just setup the ifr table one time for the injectors & then not touch it...I've only had to touch it up on one car so far & it worked well but I definitly wouldnt recommend it since it throws the fueling in all of the other tables off.
Originally Posted by 00camarossMV
I was just wondering if I should change the maf table or scale down the ifr table to compensate for positive ltft's at idle. It's running pretty lean and it's just killing my eyes. The maf is stock but i have a k n, smooth bellows, and airlid. I have a 226/230 112+4 cam and ported heads which i'm sure is contributing to the problem. I know you aren't supposed to change the maf table if it is stock but I have the lid and k n before the maf leading me to believe that i should change that table. Any suggestions? Thanks in advance.
I cant believe you have a stock maf table yet you have that cam.
I would use the IFR tables If I were still using Edit. Thats the way I used to do it, I ran like that for years(Since 2002 Before EFI Live / Auto VE days) with no Bad effects. I tested an IFR tune against a Wide band and my tune was pretty much dead on using the IFR ajustments.
BTW, if you ajust IFR so that your L- trims are a little negative the the car's computer will pull fuel a little to were the AFR will be ~ 14.7 crusing.
BTW, if you ajust IFR so that your L- trims are a little negative the the car's computer will pull fuel a little to were the AFR will be ~ 14.7 crusing.
Last edited by SmaknaSS; Jan 18, 2007 at 05:21 PM.
