Hal Fisher

Really got three questions:

1. Is WOT always open loop?

2. If so, at WOT is adjusting just the Open Loop AFR vs Coolant Temp. vs MAP the only thing that sets the AFR or are there more tables than that?

3. If so what is the formula setting AFR at WOT with MAP at 100 (or more)?

Hal

shoebox

WOT is not open loop. It is PE mode in closed loop.

Hal Fisher

Does it go into open loop when the maf goes over value (blower application)?

Hal

WS6T3RROR

No, it just reads the max airflow value its able to for as long as you exceed that value and it wont continue to add fuel to match the airflow.

mzgp5x

I have a 97ss with 383ci D1. OBD2. The MAF sensor can post a high freq threshold error when it exceeds sensor max airflow. I have fixed this with LT1__edit ver. 2.2. I set the MAF from 10.7k to ~65k+. I think you can also do this with the WOT cal curve. Also, I have zeroed PE vs. temp after much road testing. I used an AFR DynoJet unit to tune WOT mode and also closed loop part throttle AFR fueling. It was very difficult to tune w/o the DynoJet wideband unit. I also have changed the BLM matrix learn point, and, set the BLM index to 1 @ WOT mode. I have also re_cal the MAF sensor for better AFR performance @ low speed cruzing. Depending on your fuel system and the type of injector, cal settings cal varry depending on your blower efficency/ cam regarding air delivery. I run a completely modded fuel system with (2) Walbro pumps and 72# Seimens Inj peak and hold type. B.

Hal Fisher

Does setting the maf tables to read that high allow it to continue using it or does it still only support the lower portion but just not fail and cut fuel?

Hal

95Blackhawk

Hmm, my OBD I experience shows that the MAF is ignored when in PE mode.
Just so I am not confusing anyone, is this different with OBD II?

WS6T3RROR

It is most certainly used when in pe mode. Go ahead and fatten up the maf tables above 200g/sec by 5%, she will be plenty rich after that. Or if you are all tuned up in maf mode switch to speed density and you will see yet a different wot a/f ratio. A dirty maf will also make cars run stupid rich because the g/sec will be way too high compared to actual airflow.

When I tune in maf mode in person I set the pe table to whatever a/f I am targeting (usually just the coolant table and the rpm table at zero until i get what i want), and then adjust the higher airflow maf tables until that is what I get. Tuning with pe vs rpm is a lot like feeling around in the dark by comparison. Maf error is not generally consistent and airflow readings are not always going to match the rpm the same every time due to many reasons.

As for the case of the supercharged cars, they actually have the ability to max out the maf, and airflow continues to increase but no matter what you do the maf will not read the increase. What most people do is to increase the pe vs rpm to try and account for the continuing increase in airflow. While people do get away with that a lot of the time its really not that correct. The reason being is that the ve is mostly a function of the mechanical parts of the engine, the actual mass of air you move through the engine can vary a huge amount with air pressure changes and temperature changes (density increase/decrease more or less mass in the same volume). Now if you correct with the pe vs rpm table you have no way to handle the change in mass flow and if you tuned on a hot day it will be lean on a cold day and if you tuned on a cold day it will be rich on a hot day. For this reason I prefer to use a 2bar speed density tune when it comes to boost, its a royal pain on the lt1. That is one of the big advantages of the ls pcm is you don't get stuck with a bunch of scaled numbers etc.

Hope all that made sense.

95Blackhawk

Sorry but I gotta disagree. I have BLM locker on my tune. This forces the computer to go 128 during PE mode. Doing so, it doen't rely upon the MAF for fueling. Note I am talking OBD I and NA.

This is confirmed because I have a messed up MAF. For some reason it will flip out when above 220 gms/sec and give erroneous data that will cause the car to go lean and then rich (bucking)...if I don't have PE mode enabled. Because of my BLM locker, I don't ever worry about it even though I consistently go above 220 gms/sec. Car runs smooth as anything in those upper RPM's when in PE mode.

However, after all this, I may be confused since we are talking boosted situations.

Injuneer

What possible logic would there be for the PCM to ignore the MAF sensor at WOT? You have a high precision mass air meter, capable of measuring mass air flow up to 471 grams/sec, and your going to shut it off and rely on speed-density to calculate mass air flow? Where is the logic in that?

What has locking the BLM got to do with the MAF flow? The BLM is used in the equation that corrects the fuel requirement AFTER the PCM has read the mass air flow from the MAF sensor, and divided it by the target A/F ratio to arrive at the required mass fuel flow. Locking the BLM simply tells the PCM not to correct fuel flow for what it learned about the A/F ratio correction in closed loop.

There is no difference between OBD-I and OBD-II in this respect. "OBD" refers to the "diagnostics", not the logic used to control the engine. The PCM is not equipped to change the logic it uses for fueling the engine based on whether its running an NA engine or a forced induction setup.

WS6T3RROR

The maf is always used in maf mode, I don't care if its open loop closed loop pe whatever the maf is used; na boosted or juiced the maf is used in maf mode.

Do not disable pe mode for high load conditions. I use the blm locker too, it just eliminates whatever error there was before you entered pe mode. It has nothing to do with the maf sensor function.

Nothing is confirmed about the maf not being used under wot, if you have a messed up maf you have messed up fueling to go with it.

mzgp5x

I have done this...
reduced MAF cal by 2% with the FI system and 72# Inj cal.
Set MAF high freq threshold to 60k+ to limit MAF high threshold error.
I set BLM vs. rpm matrix @ higher MAP values for stoic learning purposes with FI.
I also set BLM to lock @ 1 @ WOT mode enable. I have seen people relate the theroy that the OBD2 gm PCM system will cut Inj pulse valve by 1/2 upon top limit MAF Freq being exceeded. (From Christian Milard discussion quite some time ago.)
I do see the value of having closed loop mode on the street for better miles/gal. I use it. Very snappy rev performance on the street. My manifold pressure does not go under 60 kpa.
I have also zero'ed PE vs. temp, and, only use PE vs. rpm. It has been easy for me to tune for WOT mode with a wide band DynoJet O2 sensor.
My app... 97ss OBD2 383ci D1 MM6.
Thanx. B.