Ok here comes a question for all of you that use a wideband O2 to tune your WOT.

What is the correct method of tuning the upper RPM and Kpa values?
At what point is it “dangerous” to run a 14.7:1 A/F ratio?
I understand all about tuning part throttel and keep the BLMs at 128 ( lambda 1 ) under “normal” city driving.
But is that true for all RPM and Kpa levels? When does 14.7:1 not apply?
When is time to make the fuel/air mix run richer? Or do you tune all the max rpm and Kpa to a mix of lambda 1??
I have a hard time to beleive that a engine whant to run a 14,7:1 A/F at top HP and torque points, i think that is to lean.
So the questions is. How do I tune my VE tabel in the upper RPM and Kpa areas. And when do i start to richen the mix up? At top HP, top torque or top rpm?
And what A/F value should I aim for at that point?

thanks

 

What is the correct method of tuning the upper RPM and Kpa values?

I don't know about correct but the method I use is to first fill in the table below 80 kpa in open loop so that the a/f ratio from the wide band matches the a/f ratio that was commanded. This involves also setting the iat and cts corrections so that they track through different temps. Once this is done I add the correction that was required to the 80 kpa row to both the 90 aand 100 kpa row. This gives a good guess at a starting VE. Next I start with a commanded PE air/fuel ratio of 11.5 and tune the ve tables to match the wide band output to that same 11.5. This should give the correct VE for the table. Then you can reduce the fuel by the commanded PE air fuel ratiountil the car slows down. Then go back to the richest fastest setting.

At what point is it "dangerous" to run a 14.7:1 A/F ratio?

That depends on your engine and your timing. As a rule of thumb I would say don't go over 80 kpa and be conservative with your timing.

I understand all about tuning part throttel and keep the BLMs at 128 ( lambda 1 ) under "normal" city driving.
But is that true for all RPM and Kpa levels? When does 14.7:1 not apply?

Whenever it doesnt fit what the engine wants. I have one completely stock motor that hates closed loop. It does much better in open loop at 14.4.


HTH

John

 

so richer then 11.5:1 is not to recomend?




the method I use is to first fill in the table below 80 kpa in open loop so that the a/f ratio from the wide band matches the a/f ratio that was commanded.

Does that mean that its ok to have the car running a 14.7:1 A/F even at high rpms, just that you dont go over 80Kpa? Like 14.7:1 6000rpm @ 80Kpa?

Do you use the PE adders to achive a 11.5:1 @ 90-100kpa , or do you use the ve tabels for that?

 

so richer then 11.5:1 is not to recomend?

Normally for N/A engines between 12-13 is where you will find the best ratio for power. The reason I said to start at 11.5 is for a safety margin. If you put 80% VE in your table but the value the engine develops is 90% then the commanded 11.5 will turn into a 13.0 actual ratio. If you had started at 12.5 then this would have been way to lean. It is to keep you out of trouble



Does that mean that its ok to have the car running a 14.7:1 A/F even at high rpms, just that you dont go over 80Kpa? Like 14.7:1 6000rpm @ 80Kpa?

That depends on the engine. The extra fuel is used for cooling. At higher rpms your engine may require it. I would think that it would be unlikely that you would see 80kpa at 6000 RPM with the throttle closed enough to turn off PE mode. I would not increase the high rpm tps threshholds.

Do you use the PE adders to achive a 11.5:1 @ 90-100kpa , or do you use the ve tabels for that?

I use the PE adders to achieve a commanded ratio of 11.5. The VE tables are for establishing volumetric effeciency. The ECM uses the VE table, the cylinder volume, the air temp, and coolant temp to establish the actual mass of air that will be drawn into the cylinder. That mass is divided by the air fuel ratio to establish the mass of fuel to be injected. using the injector constant the ECM calculates how long to open the injector to recieve that mass of fuel. If you lie to the computer by using the VE tables then the volume of air calculated will be incorrect. When the air temp and or coolant temp changes the mass of air will be incorrect and the actual ratio will have drifted.

HTH
John

 

so what you say is:

Tune the car to a 14.7:1 A/F at all RPM ( as you can without engage PE). Then use the numbers from the 80 kpa area ( at the same rpm ) to copy to the 90-100 area.
Then "just" use pe adders and watch the wideband?

 

Tune the car to a 14.7:1 A/F at all RPM ( as you can without engage PE).

Yes.

Then use the numbers from the 80 kpa area ( at the same rpm ) to copy to the 90-100 area.

Not quite. You want to add the difference between the stock VE and your new VE.

For example if the stock VE at 3600 RPM and 80 kpa is 89.1 and your tuned value is 94.1 then you find the difference which is 5.0. Then you add that 5.0 to the 90 kpa range and the 100 kpa range at 3600 RPM. Basicly you are trying to take an educated guess at the VE before you test it.

Then "just" use pe adders and watch the wideband?

I believe I may have misled you here by being vague. You will set the commanded af ratio to 11.5 by using the PE adders. Then you watch the wideband. You will add or subract from the VE table to make the actual af ratio measure by the wide band match the commanded ratio of 11.5. By doing this you have found the actual VE. You know that if your injector constant matches the actuall fuel flow of the injectors and the measured a/f ratio matches the commanded af ratio then the amount of airflow calculated is the actual airflow. After doing this when you change the commanded af ratio using the PE adders then the measured af ratio should closely track that. (if you change to a commanded 12.0 then the wide band should read 12.0 without any ajustment to the VE table.)

You should also record what your coolant and intake air temps are so that as the outside air temps change you can adjust these tables so that the ECM tracks correctly through changing air temps and coolant temps.

HTH

John

 

Well put.
No,
Very well put.

 

got some things that needs to be explaind ( im having little troubel with the english, from sweden... ).

you say: "You will set the commanded af ratio to 11.5 by using the PE adders. ."

I dont understand how you set a "commanded AF ratio in the pe adder tabels? I just thougt the pe adders like, "PE %change to fuel / air ratio vs rpm" only added a certin amount of fuel to the VE tabel? Like if you have 10% @ 4400rpm in your "PE %change to fuel / air ratio vs rpm" tabel. The AF would be the VE cell numbers you are in PLUS 10%fuel?


Mayby I dont understand correct how the PE adders work.

My ide is this, please comment:

zero out your ( this is for tuner cat ). "PE %change to fuel / air ratio vs rpm", and "PE %change to fuel / air ratio vs coolen temp"

Then you tune your VE tabel up to 80Kpa to a 14.7:1 AF.
Then you start with the PE tuning for a 11.5:1 AF by adding number in the tabels i mention abow?

I really try to understand what you are saying. But im not...

 

Mayby I dont understand correct how the PE adders work. I tought that the pe adder tabels like the "PE %change to fuel / air ratio vs rpm" in tuner cat, whas only adding a certin amount of %,to the actual number that is in the VE cell you are in. Not that you could print in a commanded af ratio direct in the pe adders?

WOT AFR = 6553.6/((%FUEL AIR X CTS + %FUEL AIR X RPM + 128) * 445 (STIOCH))/256)

Use the formula from the hack to figure out what the % fuel air X RPM value should be.

My ide is this, please comment:

zero out your ( this is for tuner cat ). "PE %change to fuel / air ratio vs rpm", and "PE %change to fuel / air ratio vs coolen temp"

I would not zero out any PE% change table. Ever. This will give a PE A/F ratio of 14.7 (or whatever you stioch is set ) For what you are trying to do you should leave the coolant table as is. Change the rpm table to make the a/f ratio you need. make sure you are at temp (80 C or more) when testing. Later you can adjust fuel using the coolant table to meet your engines needs at other temps.

Then you tune your VE tabel up to 80Kpa to a 14.7:1 AF.

Your scanner should give you a commanded AFR as part of the data. It should also tell you if you are in PE mode. As long as you are not in PE mode you may use BLM's or a wide band in open loop to fill in your table. Once you have set the %fuel X RPM table then when you are out of PE adjust your VE table to give a blm of 128 or a wide band reading of the commanded a/f ratio (14.7 with stock setting) Once that is done then adjust the VE table to provide a safety margin. Then enter PE mode and adjust the VE table to provide the commanded a/f ratio(11.5 for PE mode). Once you have done this you should not have to adjust your VE table again. Whenever your want a different air fuel ratio you simply change the WOT a/f ratio by adjusting the %fuel air X RPM table.
The point of doing this is to ensure that the commanded ratio is the delivered ratio.

I really try to understand what you are saying. But im not...

I am definately not a great teacher. Never have been. Feel free to ask whatever you need I will do my best to help explain.

HTH

John

 

Well put.
No,
Very well put.


Thanks although I feel I only reworded what another tuner has shown me to be the correct way

John

 

Wow this is getting more and more interesting!
I hope you dont mid help me with this.
Could you explain about the WOT AFR = 6553.6/((%FUEL AIR X CTS + %FUEL AIR X RPM + 128) * 445 (STIOCH))/256)
, and how i apply that formula? Im lost there..

So what you are saying is that in PE mode the car dont look at the VE tabels at all just what the WOT AFR = 6553.6/((%FUEL AIR X CTS + %FUEL AIR X RPM + 128) * 445 (STIOCH))/256), and what you have printed in your PE adder tabels? Im a bit lost right now?
So if that is true you only tune the upper VE tabel for a smooth transaction from PE to closed mode?

Dont give up on me, this is really something i whant to learn..

 

32V_DOHC:
For example if the stock VE at 3600 RPM and 80 kpa is 89.1 and your tuned value is 94.1 then you find the difference which is 5.0. Then you add that 5.0 to the 90 kpa range and the 100 kpa range at 3600 RPM. Basicly you are trying to take an educated guess at the VE before you test it.

I was reading in another post that if your VE is up in the 90's, you need to adjust the injector constant. Down?
True? Opinion? Wives tale? I'm clueless?

By (STOICH) do you mean 14.7?
Or is it a called up constant that can be whatever you want it to be. Like 14.4?

 

Wow this is getting more and more interesting!
I hope you dont mid help me with this.
Could you explain about the WOT AFR = 6553.6/((%FUEL AIR X CTS + %FUEL AIR X RPM + 128) * 445(STIOCH))/256)
, and how i apply that formula? Im lost there..

%FUEL AIR X CTS = The value from this table

;--------------------------------------------------
; PWR ENRICH F/A %CHG vs COOLANT
; *** WOT ***
;
; ANHT, TYPE $8D
;
; TBL = (LAMBDA * 256) + 128
;--------------------------------------------------
L860D: FCB 8 ; TABLE LENGTH +1
;
; LAMBDA C DEG c
;------------------------------
FCB 140 ; 0.546 -40
FCB 125 ; 0.488 -16
FCB 112 ; 0.438 8
FCB 86 ; 0.336 32
FCB 58 ; 0.227 56
FCB 58 ; 0.227 80
FCB 58 ; 0.227 104
FCB 58 ; 0.227 128
FCB 58 ; 0.227 152
;-------------------------------------------------

%FUEL AIR X RPM = The value from this table

;--------------------------------------------------
; POWER ENRICH FUEL/AIR % CHG vs RPM
; *** WOT ***
;
; ANHT, TYPE $8D
;
;
; TBL = LAMBDA+128/256
; TBL = (% CHG * 1.28) + 128
;--------------------------------------------------
; LAMBDA W RPM
; ---------------------------------
L8617: FCB 113 ; 0.941 0
FCB 113 ; 0.941 400
FCB 113 ; 0.941 800
FCB 113 ; 0.941 1200
FCB 115 ; 0.949 1600
FCB 115 ; 0.949 2000
FCB 115 ; 0.949 2400
FCB 137 ; 1.035 2800
FCB 128 ; 1.000 3200
FCB 160 ; 1.125 3600
FCB 150 ; 1.086 4000
FCB 157 ; 1.113 4400
FCB 138 ; 1.039 4800
FCB 138 ; 1.039 5200
FCB 138 ; 1.039 5600
FCB 138 ; 1.039 6000
FCB 138 ; 1.039 6400
;--------------------------------------------------

STOICH is this constant

L841A: FDB 0445 ; STOCH AF RATIO 14.7
; (ARG = 6553.6/RATIO)

For example at 80C and 4800 rpm the formula is

WOT AFR = 6553.6/((58 + 138 + 128) * 445)/256)

Do the math and you get

WOT AFR = 11.63


So what you are saying is that in PE mode the car dont look at the VE tabels at all just what the WOT AFR =
6553.6/((%FUEL AIR X CTS + %FUEL AIR X RPM + 128) * 445 (STIOCH))/256), and what you have printed in your PE
adder tabels? Im a bit lost right now?

No. The VE table has nothing to do with the fuel ratio. In order to calculate how much fuel to inject the ECM must know 3 things.

1. What is the size of the injector. This allows the ECM to calculate how long to open the injector for the mass of fuel required.
2. The desired air fuel ratio. This allows the ECM to calculate the mass of fuel required from the mass of air flow through the engine.
3. The mass air flow through the engine. In this system mass of air per cylinder is calculated from inputs and constants.

PV = nRT

Pressure is measured by the map sensor.
R = is a constant
Temperature is the air temp. The ECM takes the MAT signal and blends it with the CTS to account for downstream heating.
Volume is the volume of a single cylinder. However we know that the cylinder does not fill completely. The volumetric effeciency is the percentage of the volume that would be filled at that pressure. The VE tables tell the computer what percentage of theoretical air flow the engine is developing at a given RPM and MAP.

Basicly the ECM uses the information on the PROM and from the sensors (MAP RPM MAT CTS) to calculate the mass of air to be drawn into a cylinder during the intake stroke.

Then it uses information on the prom and from the sensors to calculate the air fuel ratio.

By dividing the mass of air by the air fuel ratio the ECM calculates the mass of fuel to be injected.

By dividing the fuel mass by the injector constant the ECM calculates injector on time. It will also add some time for opening which varies by battery voltage.

The short version of how to know what to change is simple. Choose a test point and look at your data. You should have at a minimum a wide band reading at that point and a scan tool data log that shows commanded A/F ratio. Compare the wide band ratio to the commanded ratio. If the wide band and the commanded ratio are the same ratio (eg both 11.5) and you want a different ratio then change the %PE ratio by RPM table. This will change the commanded ratio. The wide band (measured) ratio will also change. It should stay the same as the commanded ratio(eg now both are 12.0)

If the wide band and the commanded ratio are not the same you should adjust the VE table to make them the same. For example if the commanded ratio is 11.5 but the wide band measures a ratio of 12.0 then adding to the VE table will bring the wide band ratio up to 11.5. Once the wide band agrees with the commanded then if you want a different ratio then change the %PE by RPM table to adjust the commanded ratio.

After you adjust the VE table the first time you get a good air temp swing you may notice that the commanded ratio and the wide band do not agree. This time adjust the air temp correction to bring it back in line. This way your a/f ratio will always be the commanded value regardless of temp, map, or rpm.

So why bother with all of this. Most of it is ease of changes and consistancy. If you get the air flow right then if you change the commanded a/f ratio you will get that ratio regardless of conditions. If you tune by only changing one table until you get the wide band ratio you want then when the conditions change the ratio may be different. This is a problem because condition are ever changing. You end up chasing your tail because yesterday it was 80F outside and this mornig it is 55F and your not getting the same ratio you set it for last night.

So if that is true you only tune the upper VE tabel for a smooth transaction from PE to closed mode?

No you tune the VE table so that the ECM calculates the actual mass air flow.

HTH

John

 

I was reading in another post that if your VE is up in the 90's, you need to adjust the injector constant. Down?

Make the injector constant what it is. IOW if you have 24 lb/hr injectors rated at 43.5 psi and your fuel pressure is 43.5 psi then used 24lbs/hr for your constant. If you have a strong motor you may get over 90% VE and thats OK.

By (STOICH) do you mean 14.7?

I mean the value at L841A on the PROM.

HTH

John

 

32v_dohc best post ive read in a long time. its funny how methods all sort of coalesce into one best method over time.

 

wow!!! thank you. You just explaind what its all about. THank you sir!

:hail: :hail: :hail: :hail: :hail:

 

I com to think of something.
If you raise the fuel pressure wount that affect the set fuel ratio in the chip during pe?

 

Yes it will, but if you change the fuel pressure you should change the injector constant to reflect the new flow rate.

 

ahh ok. could you tell me the procedure on that one?

 

And I'll post this yet again ...

Back in 2000 I identified a little problem in how the PE table percentages don't seem to be accurate when comparing to the actual hac AFR.

https://www.thirdgen.org/techbb2/sho...threadid=37236

FURTHERMORE - be careful because GMEPro and TunerCat differ their percentages by 2 fold!

To really see the AFR's you need to calculate the AFR in 3D vs RPM and Coolant. Check it out in a custom program I wrote where I can change the AFR directly instead of screwing around with percentages. Please note that this is the stock AUJP.

Tim

 

thank you sir

WHat program is that u are using?

 

It's a program of my own design. Changing AFRs via using the 'percentages' that other programs use can be cumbersome and confusing. The percentages do not mathematically match up to AFR change ... AND they aren't intuitive. Now if I need to change the WOT AFR by 1.5 I can just change it by 1.5 and then verify with the WideBand. It's been a very good tool.

Tim

 

nice Is it for the buplic?

 

I've been following this thread closely, this is good reading material. But now it is time I put my 2 cents in and ask a Q.

How does the above tuning method, via John, apply to a MAF equipped system?(165, $6E) It looks like he is calibrating the WB via the VE tables, to make sure you are getting the AFR out. Then start changing the PE tables as needed to get the WOT AFR optimized. But with a MAF what would you do? If your BLMs are fairly decent, just start with that 11.5 number, and adjust lean as needed?

I set up a spreadsheet very similar to TRAX's a while ago. But when I started reading this post, I had to get the sheet back out and start playing. I have 3-3D tables, comparing 3 bins. Right now I can change the 2 table % and cacluclate the WOT AFR. Just got to tweak the sheet so I can input the AFR and get the % change back out. Can you say reverse engineering?

PS Trax, if you calculate the AFR using your 2 different methods, in your post, you get close, but NOT exact AFR calcs. So which is right

This shtuff rocks!

 

As far as comparing a MAF to MAP system,
LV8=VE,
MAF tables and scalars = VE Table.

They're load calculations, and calculated air flow.

They both have a PE% vs RPM,
and a commanded PE AFR.

 

Significant figures. 11.267 ... 11.288 ... for all potential purposes it's 11.3.

Tim

 

Nope. I made one a long time ago for public domain and posted it at DIY's FTP site. That one has some bugs in it. I fixed the bugs but I could never figure out how to update the file on the FTP site so I gave up on the public version of it. Maybe one day when I have more time. It also has a compare function, does $6E, $32, and $32B ... and also has a bunch of other useful tools built in.

Tim

 

I don't have a commanded AFR parameter in my scan tool. (EASE Diagnostics). So can I assume 14.7 afr at part throttle, and when in PE mode just got to calculate it out based on all the conditions?

I was just asking what to change in $6E MAF, in order to get the commanded PE AFR to match the WB.

IE here are some numbers from today's scan in PE mode.

MAF 170-204 gm/s
LV8 199-216
O2 0.93v
TPS 4.33v
IPW 8-10mS

Perhaps I can adjust the MAF table 5 and 6 to get the AFR right? Or what about the open loop tables?

 

;--------------------------------------
;PE vs RPM
;Val = % enrichment / 0.781225 + 100
;
;% RPM
LC515:
8F ;0
8F ;400
88 ;800
88 ;1200
80 ;1600
80 ;2000
88 ;2400
88 ;2800
80 ;3200
76 ;3600
76 ;4000
76 ;4400
76 ;4800
76 ;5200
76 ;5600
76 ;6000
76 ;6400

This is the kind of stuff where an ecm bench sure makes life easy, and saves alot of wear and tear on an engine.
Some of the codes have some really strange spots in them for what happens to the DC, PW.

 

This one deserves a "sticky"

Excellent post. Lots of great info.

Trax - you KNOW you are gonna get a whole bunch of e-mails begging for that slick AFR program you have..... mine is on the way Great work.