MAF/MAP Pegged - What does the ECM do?
07-29-2014, 03:45 PM
#1
MAF/MAP Pegged - What does the ECM do?
Hey guys,
I recently bought HPTuners and while I'll leave the tune to the local pro for now, I've been spending hours logging and reviewing the logs.
I've got some upgrades planned including a 2bar MAP and conversion to SD, but I'm curious what the ECM does in my current situation.
A&A v3Si, 3.48" pulley, headers/catless x-pipe, GHL bullets, no other engine mods.
MAP and MAF both peak somewhere north of 4k. Does the ECM go straight to PE table and use Stoich/EQ from that table for fuel exclusively?
I'm asking because logged commanded AFR matches Soich/EQ from PE, but not what I see on the dyno chart where AFR is higher by ~1.2. Commanded from log and Soich/EQ from PE ~10.6, dyno shows 11.8+
Can't seem to find a conclusive answer on this.
Thanks
I recently bought HPTuners and while I'll leave the tune to the local pro for now, I've been spending hours logging and reviewing the logs.
I've got some upgrades planned including a 2bar MAP and conversion to SD, but I'm curious what the ECM does in my current situation.
A&A v3Si, 3.48" pulley, headers/catless x-pipe, GHL bullets, no other engine mods.
MAP and MAF both peak somewhere north of 4k. Does the ECM go straight to PE table and use Stoich/EQ from that table for fuel exclusively?
I'm asking because logged commanded AFR matches Soich/EQ from PE, but not what I see on the dyno chart where AFR is higher by ~1.2. Commanded from log and Soich/EQ from PE ~10.6, dyno shows 11.8+
Can't seem to find a conclusive answer on this.
Thanks
07-30-2014, 03:13 AM
#2
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St. Jude Donor '13-'14-'15
Rather confusing what you're asking about 1st if you are planning an SD tune in the future you will NOT be using the MAF at all
But If you are trying to sort out your MAF and MAP tables in your current tune that is something else
MAP ---- I assume you car came N/A from the factory---so the MAX MAP in your tune can only be atmospheric pressure 14.6 A supercharger of course creates pressure beyond the atmosphere You can install a custom operating system for a boosted application
However it's not what most do as there are other ways around it
MAF --- You MAF table is in HZ--Typically you reach the end of the HZ table around 450-500 RWHP --When you go PAST the end of the MAF table the ECM will use the last entry from there on--( could make it lean)
The MAF table is used for fueling at P/T up to 4000 RPM's and makes corrections to the stoich 14.68 via your LTFT fuel trims---Beyond 4000 it is used as a reference in a formula to set the final actual AFR
Rule of thumb
Whatever the fuel trims are "JUST BEFORE GOING TO WOT" if positive will be added to your WOT PE fueling as a safety
However a negative fuel trim "JBGTWOT" will always lock on a "0" fuel trim
That's why you want all your PT trims to be slightly negative or exactly "0"
example:
If you have a +5 LTFT JBWOT then when you go to PE it will add 5% fuel
So if you commanded a 10.6 AFR you will end up with a 10.0
A positive trim will always make your actual AFR Richer than commanded
Now in your case where you actual AFR is leaner:
Where did you put the wideband 02 ? before or after the cat ??
Where on the HZ table do you end up in 3rd gear WOT ? Most HZ tables end around 12500 HZ---
Have you done any VE table tuning ???????
Most heavily modded engines require VE tuning in order to get the Cammanded PE fuel to Match the Actual WOT fuel---
Let me know the details above--very important on what to do next----
But If you are trying to sort out your MAF and MAP tables in your current tune that is something else
MAP ---- I assume you car came N/A from the factory---so the MAX MAP in your tune can only be atmospheric pressure 14.6 A supercharger of course creates pressure beyond the atmosphere You can install a custom operating system for a boosted application
However it's not what most do as there are other ways around it
MAF --- You MAF table is in HZ--Typically you reach the end of the HZ table around 450-500 RWHP --When you go PAST the end of the MAF table the ECM will use the last entry from there on--( could make it lean)
The MAF table is used for fueling at P/T up to 4000 RPM's and makes corrections to the stoich 14.68 via your LTFT fuel trims---Beyond 4000 it is used as a reference in a formula to set the final actual AFR
Rule of thumb
Whatever the fuel trims are "JUST BEFORE GOING TO WOT" if positive will be added to your WOT PE fueling as a safety
However a negative fuel trim "JBGTWOT" will always lock on a "0" fuel trim
That's why you want all your PT trims to be slightly negative or exactly "0"
example:
If you have a +5 LTFT JBWOT then when you go to PE it will add 5% fuel
So if you commanded a 10.6 AFR you will end up with a 10.0
A positive trim will always make your actual AFR Richer than commanded
Now in your case where you actual AFR is leaner:
Where did you put the wideband 02 ? before or after the cat ??
Where on the HZ table do you end up in 3rd gear WOT ? Most HZ tables end around 12500 HZ---
Have you done any VE table tuning ???????
Most heavily modded engines require VE tuning in order to get the Cammanded PE fuel to Match the Actual WOT fuel---
Let me know the details above--very important on what to do next----
Last edited by tblu92; 07-30-2014 at 03:17 AM.
07-30-2014, 10:30 AM
#3
Yes, stock from factory = no blower. I'm aware of the need for 2bar OS and why MAP is pegging. I am going to 2bar and SD for these reasons. Due to pegging the MAP early under boost, my tune goes MAF quickly..2600rpm vs 4k where I go > 100kPa @ WOT. LTFTs are off. Common practice by tuners for boosted applications. I've read about this on LS1tech and HPtuners. Many leave LTFTs off. STFTs look good < 3-5% from 0. Stoich is set @ 14.62.
WB was in the tailpipe. I'm installing an AEM permanently. No cats. I don't believe I logged MAF HZ. I can tell you I hit 512g/s around 4k RPM. The VE table was tuned after I installed the blower.
I asked about the mismatch between commanded afr with PE Eq of 1.3+ at high RPM and observed AFR @ 11.9 or less and the answer I got from the tuner is that under boost the injector effectively shrinks so you either have to change PE or change MAF and it's better to tune for actual airflow due to other dependencies.
WB was in the tailpipe. I'm installing an AEM permanently. No cats. I don't believe I logged MAF HZ. I can tell you I hit 512g/s around 4k RPM. The VE table was tuned after I installed the blower.
I asked about the mismatch between commanded afr with PE Eq of 1.3+ at high RPM and observed AFR @ 11.9 or less and the answer I got from the tuner is that under boost the injector effectively shrinks so you either have to change PE or change MAF and it's better to tune for actual airflow due to other dependencies.
Last edited by jmxp69; 07-30-2014 at 10:33 AM.
07-30-2014, 02:11 PM
#4
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St. Jude Donor '13-'14-'15
The only way to see if the MAF is maxed out or "pegged" is to log the MAF HZ table
If you still have your cats installed---reading the AFR's from the tailpipe will read about .2-.3 HIGHER than commanded as the cats clean up the exhaust somewhat
If you still have your cats installed---reading the AFR's from the tailpipe will read about .2-.3 HIGHER than commanded as the cats clean up the exhaust somewhat
07-31-2014, 05:49 PM
#5
The scanner chart has MAF g/s. I didn't really examine how it determined the value, but it's got to be safe to assume it's Hz derived isn't it? Understand cats clean it up, but I'm about 10.6 commanded vs 11.85 actual.
What I'm really trying to understand is the behavior of the ECM when MAF and MAP are pegged. What does it do when it is getting more air than it can measure at WOT? Is RPM eq ratio from PE table the answer?
What I'm really trying to understand is the behavior of the ECM when MAF and MAP are pegged. What does it do when it is getting more air than it can measure at WOT? Is RPM eq ratio from PE table the answer?
07-31-2014, 10:08 PM
#6
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St. Jude Donor '13-'14-'15
It gets very complicated !!!! The PE AFR is supposed to command the AFR however the MAF signal also can be adjusted to add or subtract fuel at WOT
The MAF PID you need to make does not use grams per second--
-You need to make a PID that has rows on top that show RPM from 0-8000
And columns down the left side that shows MAF Frequency from 1000 HZ to 15000 HZ
THEN the DATA can show LTFT's either right of left
Then look at WOT in 3rd gear how far down the HZ the data goes--Stock I believe ends at 12500 HZ
The MAF PID you need to make does not use grams per second--
-You need to make a PID that has rows on top that show RPM from 0-8000
And columns down the left side that shows MAF Frequency from 1000 HZ to 15000 HZ
THEN the DATA can show LTFT's either right of left
Then look at WOT in 3rd gear how far down the HZ the data goes--Stock I believe ends at 12500 HZ
08-01-2014, 09:16 AM
#7
There are two ways to peg a MAF sensor:
1) Raw input signal (Hz) goes beyond the highest value recognized by the ECM/table (~12,000Hz, depending on the PCM/year)
2) Going beyond the table's maximum physical flow value (512g/s in older ECMs)
Either way, the PCM has no choice but to ASSume that flow has somehow stagnated at the highest/last value seen, even if the actual flow is still increasing. The old school band-aid for this was to modify the PE table values to ask for a richer target ratio, knowing that you won't really get what you're asking for. Your earlier example of commanding 10.6 and getting 11.8 is exactly this. The potential problem here is that you never really know what the actual air flow is, so you don't really have precise control over the delivered AFR.
The real solution if you're running a MAF is to physically change to a different MAF or housing that doesn't hit the input limit (Hz) within the expected airflow capability of the engine. This solves problem #1 above. THEN, you need to rescale the values in the tune to avoid pegging out on problem #2 above. I covered this process in my second GM training DVD with a live demo on a supercharged C6Z. It's entirely possible to make it all work just fine without resorting to a custom operating system.
1) Raw input signal (Hz) goes beyond the highest value recognized by the ECM/table (~12,000Hz, depending on the PCM/year)
2) Going beyond the table's maximum physical flow value (512g/s in older ECMs)
Either way, the PCM has no choice but to ASSume that flow has somehow stagnated at the highest/last value seen, even if the actual flow is still increasing. The old school band-aid for this was to modify the PE table values to ask for a richer target ratio, knowing that you won't really get what you're asking for. Your earlier example of commanding 10.6 and getting 11.8 is exactly this. The potential problem here is that you never really know what the actual air flow is, so you don't really have precise control over the delivered AFR.
The real solution if you're running a MAF is to physically change to a different MAF or housing that doesn't hit the input limit (Hz) within the expected airflow capability of the engine. This solves problem #1 above. THEN, you need to rescale the values in the tune to avoid pegging out on problem #2 above. I covered this process in my second GM training DVD with a live demo on a supercharged C6Z. It's entirely possible to make it all work just fine without resorting to a custom operating system.
08-02-2014, 01:13 AM
#8
Thanks for the response Greg. Glad to have that cleared up. Just got home from travel and was able to look at the log. I didn't have MAF HZ in the table, just Mass Air Flow. That's where I see it max out.
It's peaking a little later than I originally thought--6k vs 4k+.
In the tune, PE Enable MAP is 94kPa, Enable Torque = 0%, PE Delay RPM = 700. All of those conditions are true at this point in the log. PE EQ Ratio @ 6k is 1.410. Soich in tune = 14.62. So AFR commanded should be AFR/PE EQ@6k = 14.62/1.410 = 10.36 yes? So why do I see AFR @ ~11.95? Is this related to effective injector 'shrinking' under boost?
It's peaking a little later than I originally thought--6k vs 4k+.
In the tune, PE Enable MAP is 94kPa, Enable Torque = 0%, PE Delay RPM = 700. All of those conditions are true at this point in the log. PE EQ Ratio @ 6k is 1.410. Soich in tune = 14.62. So AFR commanded should be AFR/PE EQ@6k = 14.62/1.410 = 10.36 yes? So why do I see AFR @ ~11.95? Is this related to effective injector 'shrinking' under boost?
Last edited by jmxp69; 08-07-2014 at 07:41 PM.
08-08-2014, 01:10 PM
#10
That's just an indicator that the tune is off, not really the injector flow rate difference due to pressure delta. If you're running ~10psi, Bernoullii says it works out to a 9.1% difference in mass flow rate for the injector if you had zero compensation. That's a heck of a lot less than the difference between 10.36:1 and 11.95:1 delivered ratios. Some newer PCM have the injector flow rate modeled up into the boost region to properly account for this effect (IF the tuner did it right), but some older versions have nothing above MAP=baro. Ideally, you'd still want a 1:1 fuel pressure regulator in there to mechanically compensate for this too. Using the 1:1 regulator also makes idle fuel control easier.
Your tuner set it up such that the PE multiplier is the main thing adding fuel after the MAF is pegged... and nothing else, likely. So if you hit cooler air (which is denser and requires more fuel to stay at the same AFR), you'd just lean out even further. Not good.
The real solution is that you probably need a new MAF (one that has more measurement range, like the new Hitachi slot elements), and a re-tune to work with it. This new MAF will also support flows greater than 512g/s, so your tune will need to be scaled to accommodate that as well. If both of these are done, then it should be easy to simply command an AFR of ~11.8 in PE and deliver it all the time regardless of weather conditions.
Your tuner set it up such that the PE multiplier is the main thing adding fuel after the MAF is pegged... and nothing else, likely. So if you hit cooler air (which is denser and requires more fuel to stay at the same AFR), you'd just lean out even further. Not good.
The real solution is that you probably need a new MAF (one that has more measurement range, like the new Hitachi slot elements), and a re-tune to work with it. This new MAF will also support flows greater than 512g/s, so your tune will need to be scaled to accommodate that as well. If both of these are done, then it should be easy to simply command an AFR of ~11.8 in PE and deliver it all the time regardless of weather conditions.
08-08-2014, 05:58 PM
#11
Thanks for the replies Greg. I'm new at this, so you'll have to forgive me for breaking it into chunks.
I used my log and dyno runfile to put the following together. I don't have a wideband yet, so I have to rely on the dyno AFR data.
If all of the conditions for PE are met, isn't the AFR derived from the PE EQ table? I included the values I have. There are no PE adders vs coolant temp in the 140-212 range, or PE vs IAT. So what is it about the tune that's off?
My Flow Rate vs kPa table stops at 80. Seems low for a 1bar MAP sensor doesn't it?
Can PE Add vs IAT compensate for cooler air? Fortunately, I'm in Phoenix so cold air isn't a problem right now. I'm also about to convert to a 2bar SD tune. I know there are lots of folks out there with SD tunes who don't go lean because they're on an SD tune.
Sounds like you prefer scaled MAF tunes than straight SD? I know there are pros and cons to each. Chrysler still uses SD tunes, so there's obviously a way to avoid a scaled config and still have a safe operating tune that can adjust to temperature right?
On another note, I've collected a number of logs and have seen a recurring pattern--so I started researching. On my 2003 C5 LS1, I see 1-3* KR @ ~4k. I also logged a friend's C6 z06 (headers only) and saw a similar pattern.
While searching, I found a number of posts out there with LSx engines making the same observation. A couple of them started taking timing out to no avail. Is there something about the 4k range and knock sensors on LSx engines?
Appreciate your responses,
John
I used my log and dyno runfile to put the following together. I don't have a wideband yet, so I have to rely on the dyno AFR data.
If all of the conditions for PE are met, isn't the AFR derived from the PE EQ table? I included the values I have. There are no PE adders vs coolant temp in the 140-212 range, or PE vs IAT. So what is it about the tune that's off?
not really the injector flow rate difference due to pressure delta. If you're running ~10psi, Bernoullii says it works out to a 9.1% difference in mass flow rate for the injector if you had zero compensation. That's a heck of a lot less than the difference between 10.36:1 and 11.95:1 delivered ratios. Some newer PCM have the injector flow rate modeled up into the boost region to properly account for this effect (IF the tuner did it right), but some older versions have nothing above MAP=baro.
Your tuner set it up such that the PE multiplier is the main thing adding fuel after the MAF is pegged... and nothing else, likely. So if you hit cooler air (which is denser and requires more fuel to stay at the same AFR), you'd just lean out even further. Not good.
The real solution is that you probably need a new MAF (one that has more measurement range, like the new Hitachi slot elements), and a re-tune to work with it. This new MAF will also support flows greater than 512g/s, so your tune will need to be scaled to accommodate that as well. If both of these are done, then it should be easy to simply command an AFR of ~11.8 in PE and deliver it all the time regardless of weather conditions.
On another note, I've collected a number of logs and have seen a recurring pattern--so I started researching. On my 2003 C5 LS1, I see 1-3* KR @ ~4k. I also logged a friend's C6 z06 (headers only) and saw a similar pattern.
While searching, I found a number of posts out there with LSx engines making the same observation. A couple of them started taking timing out to no avail. Is there something about the 4k range and knock sensors on LSx engines?
Appreciate your responses,
John
Last edited by jmxp69; 08-08-2014 at 06:00 PM.
08-25-2014, 08:48 PM
#12
When it pegs it uses the last cell for everything above it. You need a retune if your actual AFR is that far off from Commanded. But go SD with a 2 bar before. Knock at 4k could be from to lean of a mixture. I wouldn't get on it until you address this.
The flow rate will stop at 80 no matter what and isn't the problem. Maybe I missed it but do you have hptuners?
PS, get meth and always have cool air
The flow rate will stop at 80 no matter what and isn't the problem. Maybe I missed it but do you have hptuners?
PS, get meth and always have cool air
Last edited by danieloneil01; 08-25-2014 at 08:56 PM.
08-26-2014, 12:57 AM
#13
Ya, already converted to 2bar + meth. The pegged problem is gone now. I knew I was making the conversion when I posted but I wanted to understand what the computer was doing anyway. I do have HPTuners Pro.
09-25-2014, 06:10 AM
#14
04 z06 Tuning-Problems with MAF
My zo6 had SLP Long Tubes,Vararam Intake,and Diablosport Predater Tuner(couple years ago).Problems,along with conflicting information from respected sources,led me to remove bolt ons,and return to stock.Upon my own research,this is what I found.Focusing on the VR intake,upon installing it,my tuner was consistently showing+23to25%LTFT's,when this was supposed to be something the computer would adjust to.I was'nt comfortable making a -20% or more adj.with the tuner,since the LTFT numbers were maxxed.Then I realized my maf showed 233cc's/sec,w/ stock intake,and exactly 233/sec(the same) with the Vararam.Looking in my shop manual,it states the maf has a range up to 700cc's/sec.I haven't tried to see what the HZ's read,but was motivated to post this ,respecting the knowledge displayed in this thread.No vacuum leaks,hoping to hear back. Puzzled Mr.Zee
09-29-2014, 03:47 PM
#15
If you haven't maxxed the MAF's frequency range you need to adjust it's calibration. I wouldn't make the adjustment all at once, but I would multiply your MAF calibration values by 1.1 at least for the range of airflow values you are seeing in LTFT cell 15. You will probably need to go more than this but as you noted 20-25% is a big change so tackling it a bit at a time is a good way to go assuming you are tuning yourself or can get tweaks easily and inexpensively.
What's happened is the Vararam flows air through the MAF differently than the stock intake, causing the MAF to read significantly lower. You need to adjust the MAF calibration to account for this.
11-15-2014, 12:24 PM
#16
Drifting
"What's happened is the Vararam flows air through the MAF differently than the stock intake, causing the MAF to read significantly lower. You need to adjust the MAF calibration to account for this"
what makes this happen?
what makes this happen?
Last edited by romandian; 11-15-2014 at 12:30 PM.
11-17-2014, 10:51 AM
#17
The MAF sensors are pretty simple devices that do not directly measure the full mass of air going through them. They basically detect how much the air is cooling a small heated electrical component by the airflow around it, and then extrapolate from that how much air mass must be flowing through the full MAF. The MAF then is quite sensitive to how it is positioned relative to the air plumbing around it because that affects where in the MAF's opening the air is flowing, particularly in low-flow conditions, but it can also affect high flow conditions sometimes as well.