I'm running a '92 silverado with a TBI 454, using TunerPro RT, 7060 ECM and a $85.
There are several tables that reference airflow. How is airflow calculated on a vehicle with no MAF?

 

No ideas, no comments?

 

This is a 3rd Gen site and most of the knowledge is with 3rd Gens. Any other questions are strictly a "best efforts" affair.

In general on MAP based system, GM calcuates the air based on a variety factors: MAP sensor readings, engine rpm, engine displacement, intake air temperature, coolant temperature, and % EGR function. On some vehicles their may also be a "baro" reading plus possible other sensor readings that may affect the density of the air.

As to the SPECIFIC formula for your vehicle, I'm sorry but I don't know it. Hopefully, someone MIGHT know it. But, please be aware that we are a 3rd Gen F-body website and specialize on those vehicles...and even then, we don't know everything.

 

I appreciate your information BUT do you realize how many websites, ETC recommend this site for TBI tuning?
Hell Craig Moates told me to look here when I was looking for the $85 ADS to run the TunerPro RT scanner, which BTW I MAY be the only other person to have this since he had to make it for me.
I've asked on truck forums, they either say read the stickies (which recommends this site) or they just respond recommending this site. That includes fullsizechevy, and 454ss.com, GM_ecm, etc.
I guess I'm SOL with this POS.
Thanks for the advice though.

 

Since no one else seems helpful, maybe I can explain it in an overview.
The Speed Density ECMs, TPI or TBI, use a MAP sensor to get the pressure in the intake while the engine is running. This is used along with RPM to index into a Volumetric Effficiency table (or tables, depending on strategy) and the Vol Eff percentage is then used to calculate an equivalent airflow. This number is modifed further by the temperature of the engine coolant and the air temperature (on some strategies), and adjusted by the Barometric pressure, which is taken also off the MAP sensor on key-on before the engine starts, plus also at certain times while running (again some strategies) that ASSUME the MAP in the intake to be the same as ambient pressure of the air.

This is pretty simplistic, but basically the calculation is an equation to create an airflow term from the above.

 

Don't they use a TPS too?

 

This is what is in the later model TBI PCM for constructing the airflow from the various sensors and constants programmed into the PCM. Hope you learn something out of all the clipping that I had to do. Enjoy

EDIT- Eliminated all the spaces with dashes to make it clearer. Still probably as clear as mud to the original poster though.

;~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
; Calculate mass of air in cylinder
;~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
;
;-------------------------[kPa x 256] x [VE x 256] x [cyl. volume x 222]
; Mass of air term [g] = ------------------------------------------------
;---------------------------------[air density x 45064]
;
; Note: kPa ref pressure incorperated into air density multiplier
;
;
-----LDD------L027A----------------------------;MAP kPa x 256
-----LDX------L0259----------------------------;Inv. air density val.
-----FDIV---------------------------------------;kPa / Inv. air density val.
-----PSHX---------------------------------------;Result to stack
-----TSX ---------------------------------------;Get current stack pointer
-----LDAA-----L4D8A---------------------------;Cyl volume
-----JSR-------LF1ED---------------------------;(A x X*)/256
;
-----PULX---------------------------;Get previous result back
-----STD------L025B----------------;Save it, max mass of air in cyl.term
-----LDAA-----L0254----------------;Load VE
-----LDX-----#L025B----------------;Addr. of max. mass of air
-----JSR-------LF1ED----------------;(A x X*)/256
;
-----STD------L0257----------------;Save it, mass of air in cyl. x 32768
;
;~~~~~~~~~~~~~~~~~~~~~~~~~~~
; Calculate overall airflow
;~~~~~~~~~~~~~~~~~~~~~~~~~~~
;
;---------------------------g/cyl x 32768
; Airflow [g/s] = 256 x 2 x ---------------- x revs/sec x 4
;-------------------------------65536
;
;
;
---------LDX---------L020B ------------------;Load DRP period
---------IDIV---------------------------------;Int. div., divide airflow by drp period
---------PSHX--------------------------------;Result to stack
---------LDX---------L020B ------------------;DRP period
---------FDIV--------------------------------;Fract. divide, resolve remainder
---------XGDX-------------------------------;Get result into D
---------TAB---------------------------------;Divide result by 256
---------PULA--------------------------------;Get MSB of airflow
---------TSTA--------------------------------;Test MSB of result
---------PULA--------------------------------;Get LSB of result
---------BNE---------L80ED ------------------;Bra if MSB !=0, result out of range
;
---------ASLD--------------------------------;Result x 2, now gms/sec x 256
---------BCC-----L80F0----------------------;Bra if no overflow

L80ED---LDD----#$FFFF----------------------;Clear overflow
;
L80F0---STD-----L0255----------------------;Save it, gms/sec x 256
;
;~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
; Divide mass air in cyl by AFR to get needed mass of fuel
;~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
;
;---------------------------------g/cyl
; mass of fuel [g] = 819.2 x 256 x -------
;----------------------------------AFR
;
---------LDX---------L0257 ------------------;grams of air per cyl. x 32768
---------LDAA-------L026D-------------------;AFR x 10
---------CLRB--------------------------------;Clear LSB for divide
---------XGDX-------------------------------;Swap AFR and g/cyl.
---------LSRD--------------------------------;/2
---------LSRD--------------------------------;/2
---------FDIV--------------------------------;([g/cyl x 8192]/[AFR x 2560]) x 65536
---------XGDX-------------------------------;Get result into D
;
;-Make mass fuel needed a time based PW
;
---------LDX---------L4D88 ------------------;Injector flowrate
---------IDIV--------------------------------;Int. divide, mass of fuel / mass flowrate
---------PSHX-------------------------------;Push result to stack
---------LDX---------L4D88------------------;Injector flowrate into X
---------FDIV--------------------------------;Fract. divide, resolve remainder
---------XGDX--------------------------------;Get result into D
---------TAB---------------------------------;/256
---------PULA--------------------------------;MSB of idiv result
---------TSTA--------------------------------;Test MSB
---------PULA--------------------------------;Get LSB or result into A
---------BEQ---------L8112 ------------------;Bra if MSB ==0, result is within range
;
---------LDD--------#65535------------------;Clear out of range result
;
;------------------grams of fuel/cyl
; BPW = 65536 x ---------------------
;----------------- flowrate of injector
;
L8112-----STD------L0271-------------------;Save it, sync BPW
;
From this point all the compensations can be factored in. EGR, BLM, Proportional Gains, CCP, etc.

 

Thanks for the explainations. A lot of it does make sense, obviously the last one makes too much sense for me but I do appreciate the time spent, and I do print stuff like this out most of the time to look over and figure out later when I learn more about it to better understand it.

 

Basically, as was mentioned, what all that means is to calculate airflow, you multiply the cylinder volume * number of cylinders *(RPM/2) and you get calculated air flow since theoretically each cylinder moves its calculated volume of air once every other revolution. Now if you want to get into the specifics of the speed density formula calculations of actual air volume and density and assosciated fueling, then other factors such as VE and IAT and Barometer and load (MAP or LV8) come into play. You can search "speed density calcluations" and pull up a lot of useful information. HTH

 

Thanks, will do that search. My LM-1 should be back Monday, til then its time to read a bit.
Thanks to all.

 

Quote: There are several tables that reference airflow.

I assume those tables offer variables? Give an example of one of those tables.

Is that ECU you use also used in a MAF equipped vehicle? Maybe that table(s) is not applicable to your SD TBI system? Just a guess.

 

In all the ECMs, the O2 PID tables are based on airflow since that defines the transport delay. The later ECMs/PCMs also have other tables based on airflow such as the choke decay off the top of my head. While the later computers used actual SD calculations to generate the airflow, the early TBI ECMs used a sort of pseudo-calculation to approximate the airflow, which wasnt very accurate.

 

The $85 code in the '7076 uses a routine similar to the older C3 TBI ECMS to calculate the airflow for the PID lookups. It isn't intended to be accurate, just intended to produce a value that can be used for the intended purpose. Basically it uses the MAP and RPM values to estimate the airflow through the engine. Here is that code:

The tables using this airflow value include:

SLOW o2 FILTER TIME CONST vs AIR FLOW
INTEGRATOR DELAY Vs AIR FLOW
AVG Rich/Lean THRESHOLD va AIR FLOW
Rich o2 THRSH vs AIR FLOW
Lean o2 THRESH vs AIR FLOW
EGR COMP TABLE FOR AIR FLOW IN Gms/sec
PROP DURATION OFF SET AIR FLOW (bin) vs AIR FLOW
PROPORTIONAL GAIN FLOW FACTOR vs AIR FLOW
AIR FUEL TIME OUT DECAY RATE vs AIR FLOW

RBob.

 

Which $85 mask are you looking at? I've found 2 that dont match. What are you wanting to change? What mods do you have?

I've been through the ringer on one of these 7060s. Buddy built a short rod(loves the timing) 406 with dart II's in a 3/4 ton suburban. Big intake, throttle body, Xtreme 256 cam, long tubes. When I came looking for info there was none.

It's been a bear to get dialed in but now its done. And its stout.

 

I have a 93 3/4 ton 496 tbi/4l80e Suburban with the 7060. After countless evenings of searching and reading I finally made my own .ads file back in March or April.

Where did you find a copy of the BAMY bin? I run the AWWH and I'm still having a heck of a time getting my tune together.