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Quick question: Can the C5 ECM "learn" at WOT, i.e., in open loop? No issues, just curious....
In terms of fuel, no there is no feedback at WOT or any other time the targeted AFR is not stoich, since the car only has narrowband sensors.
Long term fuel trims that are learned in part throttle can carry over into WOT though. Say the car was designed for E0 fuel but now runs E10. That learned average +5 LTFT will carry over into WOT (Power Enrichment). Positive fuel trims carry over into PE. Negative fuel trims, then LTFT is 0 in PE. Most conservative option is used.
My question is mainly to do with the fact that I recently added a Vararam setup with Vararam air bridge. To review, my C5 has a built LS7 transplanted. But I've been running the OEM C5 airbridge for years. The Vararam setup probably hasn't made a huge difference. BUT-The Vararam air bridge has made a BIG difference. The car ran good before. But now when it hits second gear (A4 trans), the car lights up the tires, and trys going sideways!! It spun a bit before when it hit second gear, but never like this. Thats why I'm concerned, because I haven't had it retuned yet. Thanks for the response!!
Since the air bridge is either right after or before the MAF, it could change the MAF curve a little bit. But it might not be enough to matter, or cause issues.
Not sure if you have any sort of scanning device, but take a quick look at LTFT driving around a different loads if you can. If you have very positive or negative trims, it would be idea to tweak the MAF curve a bit. If its say +/- 5%, I wouldn't bother at all.
My question is mainly to do with the fact that I recently added a Vararam setup with Vararam air bridge. To review, my C5 has a built LS7 transplanted. But I've been running the OEM C5 airbridge for years. The Vararam setup probably hasn't made a huge difference. BUT-The Vararam air bridge has made a BIG difference. The car ran good before. But now when it hits second gear (A4 trans), the car lights up the tires, and trys going sideways!! It spun a bit before when it hit second gear, but never like this. Thats why I'm concerned, because I haven't had it retuned yet. Thanks for the response!!
The Vararam usually needed a tune because at low throttle openings the MAF was not reading as expected by the PCM and it would cause lean codes. How did you install the Vararam? Is the MAF in the stock location or next to the throttle body?
Extra airflow due to a CAI typically requires an adjustment to your fuel trims--They will go Positive
Data logging the MAF table can help in adjustments to the LTFT's by using the MAF HZ table only exactly where needed
YES IF you have a POSITIVE fuel trim "JUST BEORE GOING TO WOT" That positive fuel trim will be added to your Commanded Power Enrichment fueling---If you have a NEGATIVE fuel trim JBGTWOT the ECM will Never remove any fueling during PE and will lock on "0" as a Lean safety
For example If you have a commanded PE fueling of 12.5 and have a Positive fuel trim JBGTWOT of like 10% That is HUGE !!!! 12.5 Plus 10% will give you a now PE fueling of 11.25 !!!
PIG RICH !!
In performance applications using Gen3 style $20 ECU you can get the performance and capability of a $2000 stand-alone unit by disabling the closed loop feature and delete the maf sensor. Now you can target any air fuel ratio for part throttle and the VE table can be devoid of spike corrections making the engine run smoother overall while increasing fuel economy and keeping combustion chambers cleaner and plugs cleaner at 15.2 to 16:1 air fuel ratio cruise/idle. It will also force you the user to learn how to properly tune the ECU to become reliable and consistent.
Here is an example from my turbo daily note 18psi of boost (exceed map 2-bar limit) by 3200rpm on the highway and managing 15's and 16's for idle and cruise
0:05 get on highway cruise note 16's
3:38 note 15.8 to 16.0:1 still cleaning plugs @ 65mph in traffic
5:18 kick out of lockup and small boost in 4th to move up in traffic
6:29 step down lightly into lockup for some boost in 4th
7:18 get off highway
8:23 downshift rip the tires loose at 50mph
9:12 slowing down for stoplight
9:20 Showing A/F Stopped at stoplight note 14.7 to 15.0 open loop steady
10:51 leave light, turbine whistle
11:30 cruising 15.6 to 16.0 housekeeping plugs
12:18 rip tires loose at 50mph 'spool character'
13:05 stopping for traffic light
13:10 show a/f for traffic light stop 15.5 walking into 14.7 to 15.0 open loop
13:52 2nd gear chirp coming leave light
If you are tuning for your own vehicle there is no reason to use closed loop as YOU are the tuner who is correcting and carrying the laptop.
If you are tuning a vehicle for somebody else you MUST use closed loop because the tuning may wander over time with atmosphere and elevation and so forth and you won't be there to witness the changes and tune for them.
Tuning open loop is much more work but the result is a cleaner more efficient engine more smooth and consistent.
Again I disagree with your tuning practices
Just because you are COMMANDING an AFR in the 15's and 16's does not mean that is your final ACTUAL AFR------- during P/T and Cruising
The only way to verify your actual AFR is with a Wideband ---- Which you obviously don't use nor know of its use Your ACTUAL AFR is most likely where it is supposed to be which is STOICH 14.7
Scientifically proven to be the most efficient AFR for gasoline during P/T
If you had an ACTUAL AFR that lean you would get melted plug tips---Pitted piston tops--and failed rings
Hardly ever does the actual equal the commanded AFR for many reasons-- Poor VE tuning----Long tube headers ---large overlapped camshafts------ also there is another program the leans out the AFR during deceleration called DFCO "Deceleration fuel cut off "
You may be college educated and smart as a whip But you are not a Pro Tuner--Just a hack
In your profile it says your hobbies are "Cars and Women"
Do us all a favor and go back to chasing women !!!!!!!!!!!!!!
Again I disagree with your tuning practices
Just because you are COMMANDING an AFR in the 15's and 16's does not mean that is your final ACTUAL AFR------- during P/T and Cruising
The only way to verify your actual AFR is with a Wideband ---- Which you obviously don't use nor know of its use Your ACTUAL AFR is most likely where it is supposed to be which is STOICH 14.7
Scientifically proven to be the most efficient AFR for gasoline during P/T
If you had an ACTUAL AFR that lean you would get melted plug tips---Pitted piston tops--and failed rings
Hardly ever does the actual equal the commanded AFR for many reasons-- Poor VE tuning----Long tube headers ---large overlapped camshafts------ also there is another program the leans out the AFR during deceleration called DFCO "Deceleration fuel cut off "
You may be college educated and smart as a whip But you are not a Pro Tuner--Just a hack
In your profile it says your hobbies are "Cars and Women"
Do us all a favor and go back to chasing women !!!!!!!!!!!!!!
Sorry you have no idea what you are talking about. The graph I shared is from my wideband obviously. And it is common tuning practice to tune 16:1 air fuel ratio we've done it to all vehicels 1,000+ since the 90's in 4 6 8 10 cylinder applications for 25 years of service 350,000 miles.
Even the OEM Manufacturers are doing it since the 80's in lean burn engines
Actual science
It isn't *my* method lol. It is how the entire aftermarket ECU world tunes their engines for max efficiency.
I've been tuning since the 90s Its always been done this way. Every car. Every application. Only fools use narrowband air fuel ratios in performance applications.
Time to grow up. Everything you know is wrong.
My car in open loop running lean 16:1 air fuel ratios for 6 years at 600rwhp 65,000 miles so far with a total of 240,000 miles on the factory 5.3L Engine 93 octane gasoline only
0:05 get on highway cruise note 16's
3:38 note 15.8 to 16.0:1 still cleaning plugs @ 65mph in traffic
5:18 kick out of lockup and small boost in 4th to move up in traffic
6:29 step down lightly into lockup for some boost in 4th
7:18 get off highway
8:23 downshift rip the tires loose at 50mph
9:12 slowing down for stoplight
9:20 Showing A/F Stopped at stoplight note 14.7 to 15.0 open loop steady
10:51 leave light, turbine whistle
11:30 cruising 15.6 to 16.0 housekeeping plugs
12:18 rip tires loose at 50mph 'spool character'
13:05 stopping for traffic light
13:10 show a/f for traffic light stop 15.5 walking into 14.7 to 15.0 open loop
13:52 2nd gear chirp coming leave light
If you actually understand how engines work and conceptualize oxygen radicals attacking hydrocarbon substrates and the thermodynamic principles behind combustion and rate of piston motion you would understand that the leaner air fuel ratios reduce EGT and reduce piston temperatures, improve efficiency and economy, reduce carbon fouling and carbon deposits, help clean the carbon out of the cylinder and maintain clean spark plugs.
Educate yourselves please I am tired of pretend wana be knowit alls copy and pasting each other bad information. You don't know !@#$ and cant be bothered to search and read shame on you.
Is peak EGT the place to be?
You might think that this chemically perfect air-fuel ratio at which EGT peaks would be where we should always operate our engines, but you’d be wrong. Just because it’s chemically perfect doesn’t mean it’s operationally useful. It’s not the mixture that produces best power, and it’s not the mixture that produces best economy. So, it’s not generally the optimal mixture for flying.
For best power, you need an air-fuel ratio of about 12.5-to-1, quite a bit richer than stoichiometric, which occurs at about 100 to 125 degrees F rich of peak. This rich mixture burns somewhat dirty (due to unburned hydrocarbons), but it also burns faster which yields a bit more power. For full-power takeoffs, we use an even richer mixture for increased detonation margin.
For best economy, you need an air-fuel ratio of about 16-to-1 , quite a bit leaner than stoichiometric and so significantly lean of peak. Such a lean mixture burns very clean and reduces combustion pressure and temperature, which is great for engine longevity but at the sacrifice of some power and airspeed.
Many people think that the leaner you go, the higher the EGT gets. This is also incorrect. Peak EGT occurs at stoichiometry- about 15 to 1 for our purposes. If you go richer than 15 to 1, EGT will drop and if you go leaner than 15 to 1 EGT will ALSO drop.
11-13-2023, 09:20 AM
Open loop learning capabilities.....
