LTFT Low FIX Found ! !
Feb 25, 2009, 07:00 PM
#16
After changing logworks, everything is making sense and I saw some interesting behavior.
I am using a Tial BOV, so I have so lift off 'issues.'
I noticed that the problem isn't directly the rich condition induced by the BOV. The real problem looks to be the STFTs. On lift off, AFRs go into the 10s, but the motor runs fine. STFTs drop to about -80% though. This then forces the AFR into the 18:1-19:1 AFR range, and this is when the car wants to stall/run rough.
Would it be possible to limit the max/min STFT values? Limiting it to say +/-25% may greatly reduce the lean conditions that cause the rough running conditions while still allowing plenty of range to allow proper adjustments under normal conditions.
I am using a Tial BOV, so I have so lift off 'issues.'
I noticed that the problem isn't directly the rich condition induced by the BOV. The real problem looks to be the STFTs. On lift off, AFRs go into the 10s, but the motor runs fine. STFTs drop to about -80% though. This then forces the AFR into the 18:1-19:1 AFR range, and this is when the car wants to stall/run rough.
Would it be possible to limit the max/min STFT values? Limiting it to say +/-25% may greatly reduce the lean conditions that cause the rough running conditions while still allowing plenty of range to allow proper adjustments under normal conditions.
Feb 25, 2009, 07:48 PM
#17
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FWIW I have a Dejon Tool Hard Pipe, Stock Airbox w/Drop In & GSC S1's. The stock box is probably helping with MAF readings quite a bit.
Idle @~950rpm & ~33hz
Car idles in open loop because of injectors (1000cc/min). Idles a tick richer than stoich in closed loop and messes with STFT/LTFT because the inj's are already at min on time.
I'm probably going with a hot wire MAF in blow through once I upgrade the turbo and intake setup (a ways away with the crappy economy).
One possible fix to run some intake combos is to study the velocity profile at the inlet of the stock setup then try to keep that same profile with the new intake setup (This is probably very hard to do). Good luck with the Karman Vortex meter research!
Idle @~950rpm & ~33hz
Car idles in open loop because of injectors (1000cc/min). Idles a tick richer than stoich in closed loop and messes with STFT/LTFT because the inj's are already at min on time.
I'm probably going with a hot wire MAF in blow through once I upgrade the turbo and intake setup (a ways away with the crappy economy).
One possible fix to run some intake combos is to study the velocity profile at the inlet of the stock setup then try to keep that same profile with the new intake setup (This is probably very hard to do). Good luck with the Karman Vortex meter research!
Feb 25, 2009, 08:51 PM
#18
Limiting the amount the STFT can change would likely reduce the problems with a VTA BOV because it would keep the ECU in check on how much fuel it pulls out trying to compensate for the rich condition. I'd rather have it run 10:1 and slowly taper back to 14.7:1 then have it run 10:1 then a second later drop to 19:1 then slowly taper back to 14.7:1.
Feb 25, 2009, 10:28 PM
#19
That's exactly what I was saying.
Limiting the amount the STFT can change would likely reduce the problems with a VTA BOV because it would keep the ECU in check on how much fuel it pulls out trying to compensate for the rich condition. I'd rather have it run 10:1 and slowly taper back to 14.7:1 then have it run 10:1 then a second later drop to 19:1 then slowly taper back to 14.7:1.
Limiting the amount the STFT can change would likely reduce the problems with a VTA BOV because it would keep the ECU in check on how much fuel it pulls out trying to compensate for the rich condition. I'd rather have it run 10:1 and slowly taper back to 14.7:1 then have it run 10:1 then a second later drop to 19:1 then slowly taper back to 14.7:1.
The maf measures that air that the bov vents to atmosphere. If you fix the bov issue it will affect other areas of the tune or cars drivability .
I'm currently running 30 psi through stock BOV crushed mod
I have run the APS and saw half of what you are talking about. I also have agency power with both vta and recirc. both valves are sitting in the garage for a reason. YMMV Good luck I truly hope it works out for you one way or another
Feb 25, 2009, 10:30 PM
#20
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Why not a run a hybrid bov or better yet a recirculatiing valve to alleviate the issue.
The maf measures that air that the bov vents to atmosphere. If you fix the bov issue it will affect other areas of the tune or cars drivability .
I'm currently running 30 psi through stock BOV crushed mod I have run the APS and saw half of what you are talking about. I also have agency power with both vta and recirc. both valves are sitting in the garage for a reason. YMMV
Good luck I truly hope it works out for you one way or another
The maf measures that air that the bov vents to atmosphere. If you fix the bov issue it will affect other areas of the tune or cars drivability .
I'm currently running 30 psi through stock BOV crushed mod
I have run the APS and saw half of what you are talking about. I also have agency power with both vta and recirc. both valves are sitting in the garage for a reason. YMMV Good luck I truly hope it works out for you one way or another
-E
Feb 25, 2009, 10:33 PM
#21
Well, for 1, I'm a fan of the Tial. I like the sound...
But I also like the idea that it will hold ANY amount of boost I EVER throw at it.
It will also flow enough air to keep a GT42 happy.
It is very well built.
Lastly, when I bought it, I also had an AEM...I've since sold the AEM.
Oh, and I've been running Tial wastegates and BOVs since like 2000. I'm a loyal customer.
But I also like the idea that it will hold ANY amount of boost I EVER throw at it.
It will also flow enough air to keep a GT42 happy.
It is very well built.
Lastly, when I bought it, I also had an AEM...I've since sold the AEM.
Oh, and I've been running Tial wastegates and BOVs since like 2000. I'm a loyal customer.
Feb 26, 2009, 05:16 AM
#22
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Logging with EvoScan yeilded the following....
Switching points are 31.25 then 37.5 then 43.75 then 50 then 56.25 then 62.5 then 68.75 then 75
These can be seen by watching the AirFlowHz request ID 1A.
Airflow MUT 2byte MOD will show a more exact measurement.
I found these out while logging idle to work on my MAF scaling. What is crazy is that when I had the HKS suciton pipe it would idle at a constant 50+/- 3 Hz. So, I put back on the stock rubber pipe it has huge spikes in MAF Hz at idle. I was able to duplicate the stock MAF Hz characteristics with putting a 45 degree silicon reducing coupler on the MAF but inside the HKS Suction pipe. So now I need to figure out how to fix the spikes. Oh and load spikes when the MAF Hz spikes. Makes my idle kind of irratic, but little to no stall issues when rolling to a stop.
Switching points are 31.25 then 37.5 then 43.75 then 50 then 56.25 then 62.5 then 68.75 then 75
These can be seen by watching the AirFlowHz request ID 1A.
Airflow MUT 2byte MOD will show a more exact measurement.
I found these out while logging idle to work on my MAF scaling. What is crazy is that when I had the HKS suciton pipe it would idle at a constant 50+/- 3 Hz. So, I put back on the stock rubber pipe it has huge spikes in MAF Hz at idle. I was able to duplicate the stock MAF Hz characteristics with putting a 45 degree silicon reducing coupler on the MAF but inside the HKS Suction pipe. So now I need to figure out how to fix the spikes. Oh and load spikes when the MAF Hz spikes. Makes my idle kind of irratic, but little to no stall issues when rolling to a stop.
Feb 26, 2009, 06:59 AM
#23
Logging with EvoScan yeilded the following....
Switching points are 31.25 then 37.5 then 43.75 then 50 then 56.25 then 62.5 then 68.75 then 75
These can be seen by watching the AirFlowHz request ID 1A.
Airflow MUT 2byte MOD will show a more exact measurement.
I found these out while logging idle to work on my MAF scaling. What is crazy is that when I had the HKS suciton pipe it would idle at a constant 50+/- 3 Hz. So, I put back on the stock rubber pipe it has huge spikes in MAF Hz at idle. I was able to duplicate the stock MAF Hz characteristics with putting a 45 degree silicon reducing coupler on the MAF but inside the HKS Suction pipe. So now I need to figure out how to fix the spikes. Oh and load spikes when the MAF Hz spikes. Makes my idle kind of irratic, but little to no stall issues when rolling to a stop.
Switching points are 31.25 then 37.5 then 43.75 then 50 then 56.25 then 62.5 then 68.75 then 75
These can be seen by watching the AirFlowHz request ID 1A.
Airflow MUT 2byte MOD will show a more exact measurement.
I found these out while logging idle to work on my MAF scaling. What is crazy is that when I had the HKS suciton pipe it would idle at a constant 50+/- 3 Hz. So, I put back on the stock rubber pipe it has huge spikes in MAF Hz at idle. I was able to duplicate the stock MAF Hz characteristics with putting a 45 degree silicon reducing coupler on the MAF but inside the HKS Suction pipe. So now I need to figure out how to fix the spikes. Oh and load spikes when the MAF Hz spikes. Makes my idle kind of irratic, but little to no stall issues when rolling to a stop.
Feb 26, 2009, 08:44 AM
#24
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I tried to rescale the intake but I could not get the Hz to go any lower than 50Hz. Then there was a huge stalling issues with the HKS pipe too. I believe this stalling was the result of the LTFT Low not being able to adjust becasue the MAF would not read in the Low range.
The "restriction", if any is very minimal since the coupling is the same diameter as the MAF output side.
My attempt is to make the HKS pipe work like stock for idle but have the advantage of smoother flow in the upper RPM.
The coupler on the MAF, inside the HKS pipe, helps to smooth the airflow to make for a more accurate Hz reading. The HKS pipe is huge on entrance to make the maf read off, therefore leaning the fuel mixture to make a few HP. The pipe works great in the upper RPM while idle suffers horribly.
The "restriction", if any is very minimal since the coupling is the same diameter as the MAF output side.
My attempt is to make the HKS pipe work like stock for idle but have the advantage of smoother flow in the upper RPM.
The coupler on the MAF, inside the HKS pipe, helps to smooth the airflow to make for a more accurate Hz reading. The HKS pipe is huge on entrance to make the maf read off, therefore leaning the fuel mixture to make a few HP. The pipe works great in the upper RPM while idle suffers horribly.
Feb 26, 2009, 11:07 AM
#25
I'm almost wondering if "smooth" wasn't what OEM had in mind. Because smooth means maintaining what is called "fully developed pipe flow" where the velocity gradient throughout the cross section is nearly parabolic. In other words, "smooth" is when the airflows the fastest at the center of the pipe and becomes slower and slower the closer you get to the tube wall.
My MAF tube has very smooth transition between the tube and MAF, a decent amount of straight after the MAF, no BOV recirculation tube, then very minimal bending and a smooth reducer to the turbo.
Contrast that with OEM. Rough surface, lots of bends, minimal straight after MAF, a BOV tube. Not really something that will develop a nice velocity profile.
Rescaling the MAF, I had to pull out ~25% on the low end to get MUT32 (estimated AFR) and the actual AFR to line up. Up above about 800 Hz though, the stock scaling was right on the money. After rescaling, my STFTs sit right around 0 under everything but right after letting off the throttle.
The fact I had to pull out fuel surprised me at first. That says for a given airflow, more is now going through the square in the center of the MAF and less around the edges, thus raising the MAF output frequency. This points to the airflow being closer to a fully developed pipe flow (highest velocity in the center of the pipe). If anything, I'm thinking the stock intake is intentionally causing turbulence to avoid fully developed pipe flow and is trying to maintain the airflow in the transition region as the airflow velocity is more even across the cross section. At high airflow rates, the flow is much more turbulent because of the higher velocities and both of the intakes end up with roughly the same flow profiles in the MAF. Likely the MAF at that point even dominates over the intake as to the velocity profile characteristics.
My MAF tube has very smooth transition between the tube and MAF, a decent amount of straight after the MAF, no BOV recirculation tube, then very minimal bending and a smooth reducer to the turbo.
Contrast that with OEM. Rough surface, lots of bends, minimal straight after MAF, a BOV tube. Not really something that will develop a nice velocity profile.
Rescaling the MAF, I had to pull out ~25% on the low end to get MUT32 (estimated AFR) and the actual AFR to line up. Up above about 800 Hz though, the stock scaling was right on the money. After rescaling, my STFTs sit right around 0 under everything but right after letting off the throttle.
The fact I had to pull out fuel surprised me at first. That says for a given airflow, more is now going through the square in the center of the MAF and less around the edges, thus raising the MAF output frequency. This points to the airflow being closer to a fully developed pipe flow (highest velocity in the center of the pipe). If anything, I'm thinking the stock intake is intentionally causing turbulence to avoid fully developed pipe flow and is trying to maintain the airflow in the transition region as the airflow velocity is more even across the cross section. At high airflow rates, the flow is much more turbulent because of the higher velocities and both of the intakes end up with roughly the same flow profiles in the MAF. Likely the MAF at that point even dominates over the intake as to the velocity profile characteristics.
Last edited by 03whitegsr; Feb 26, 2009 at 11:10 AM.
Feb 26, 2009, 01:19 PM
#26
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Ok Fluid Dynamics 101 here. I recall everything you say and agree that the MAF likes turbulence. The waves created by the turbulence is what the MAF essentially reads right?
Initially I put on the stock rubber tube to get my injectors scaled properly. Now that I have that done I am working on the MAF scaling with the hard pipe. I have had to raise the scaling number from ever point below 175. By scaling the values I am slowly eliminating the spikes that occur with an out of scale MAF.
The goal is to get the MAF to read the same way it did with the stock rubber tube.
Initially I put on the stock rubber tube to get my injectors scaled properly. Now that I have that done I am working on the MAF scaling with the hard pipe. I have had to raise the scaling number from ever point below 175. By scaling the values I am slowly eliminating the spikes that occur with an out of scale MAF.
The goal is to get the MAF to read the same way it did with the stock rubber tube.
Feb 26, 2009, 03:04 PM
#27
From reading JCSBanks write up on the MAF to Injector Pulsewidth thread, I would use the MAF Smoothing table and not the MAF Scaling table.
From other things I read on here (I think L2r99gst's thread?), the MAF scaling table has 140 added to it, so changing the values 10% does not change the fueling 10%. The MAF Smoothing table on the other hand looks to be a direct scaling according to JCSBank's thread. Thus a 10% change in that table makes for a 10% change in AFR. This is what I saw while scaling it as well and it should make things a bit easier.
My goal was to minimize difference between the target AFR (MUT 32) and the actual AFR. Using logworks, I created a math function of AFR error [AFRError = (TargetAFR - Actual AFR)/Target AFR]. Created a chart of AFR Error with MAF Frequency as the X-axis. For the Y-axis, I tried a few different things and got the best results using MAP as the Y-Axis. You get a lot of error on fuel cut (as target AFR is 14.7:1 but actual is the leanest your wideband reads) which can mess up the numbers pretty badly. Using MAP means you just ignore the row of the highest vacuum at all MAF frequencies.
From other things I read on here (I think L2r99gst's thread?), the MAF scaling table has 140 added to it, so changing the values 10% does not change the fueling 10%. The MAF Smoothing table on the other hand looks to be a direct scaling according to JCSBank's thread. Thus a 10% change in that table makes for a 10% change in AFR. This is what I saw while scaling it as well and it should make things a bit easier.
My goal was to minimize difference between the target AFR (MUT 32) and the actual AFR. Using logworks, I created a math function of AFR error [AFRError = (TargetAFR - Actual AFR)/Target AFR]. Created a chart of AFR Error with MAF Frequency as the X-axis. For the Y-axis, I tried a few different things and got the best results using MAP as the Y-Axis. You get a lot of error on fuel cut (as target AFR is 14.7:1 but actual is the leanest your wideband reads) which can mess up the numbers pretty badly. Using MAP means you just ignore the row of the highest vacuum at all MAF frequencies.
Last edited by 03whitegsr; Feb 26, 2009 at 03:10 PM.
Feb 26, 2009, 07:59 PM
#28
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I already knew about the 140 adder. After many long cruises I now have my LTFT mid fuel at +0.3906....PERFECT ! !
I am working on the LTFT low. It is currenly at +4.6875. It still has some Hz spikes that I am working to smooth out. A little more MAF scaling and I should have it perfect too.
The best part....no more stalling issues at all. The car drives nealy stock like, but with a ton more power because of my mods.
Oh and gas mileage is vastly improved. 90+ miles on 1/4 tank, i.e. from full to the first hash mark. I used to only get about 65MPG
I am working on the LTFT low. It is currenly at +4.6875. It still has some Hz spikes that I am working to smooth out. A little more MAF scaling and I should have it perfect too.
The best part....no more stalling issues at all. The car drives nealy stock like, but with a ton more power because of my mods.
Oh and gas mileage is vastly improved. 90+ miles on 1/4 tank, i.e. from full to the first hash mark. I used to only get about 65MPG
Feb 27, 2009, 01:52 PM
#29
Get a couple tanks on it and let us know. After rescaling, my car definitely seems to run better. It use to drop into the 12s on AFRs right when it went into open loop under moderate throttle, despite being programmed to smoothly drop off from 14.7:1. Now it usually sits up in the high 13s/low 14s right out of closed loop and then as load rises, drops down, just as my fuel map is setup. I haven't ran enough fuel through it to see if it hurt or helped fuel economy though.
Feb 27, 2009, 02:21 PM
#30
Also, if you are trying to automagically add/subtract based on MAFhz and AFRmap difference you may or may not want to also use LTFT + STFT, then limit to a specific TPS range (or difference in TPS from last and next cells) so that you get more consistent results.
Last edited by fostytou; Feb 27, 2009 at 02:31 PM.