Thanks for confirming closed loop-S/D operation. I was pretty sure but never tried it.

Rich

 

The PCM uses the VE tables to determine how much air is entering the engine when in SD mode, instead of an MAF. The "trims" are a correction and the O2 sensors determine that, regardless of MAF or SD.

Kevm14 was asking about acceleration enrichment however. This is akin to a pump shot on a carb

To answer your question. The PCM uses the same tables in open loop/SD mode as it does when using the MAF except instead of the MAF frequency table it relies on the VE tables.

MAF is never used for feedback, that's the O2 sensors' job. I'll simplify it even more. Think of it this way, when in MAF mode the PCM uses the MAF frequency table to determine airflow, when in SD mode the PCM uses the VE tables. Other than that, the PCM operates in the same way.

 

OK so what your tellin me is that the ECM uses the VE Tables AND the AFR x 10, Open Loop Vs Coolant Temp Vs MAP Table while in OPEN LOOP/SD Mode??

And also your saying that the ECM uses the MAF Tables AND the AFR x 10, Open Loop Vs Coolant Temp Vs MAP Table while in OPEN LOOP/MAF MODE??

Is that correct??

 

This is the last time I'm going to try and explain it, because you still do NOT understand what any of us have been saying.

To calculate the fuel required at any point in time, you need TWO things - these are totally independant pieces of information:

1 - TARGET A/F ratio.

The "the AFR x 10, Open Loop Vs Coolant Temp Vs MAP Table" is how the PCM calculates the target A/F ratio. NOTHING ELSE. Doesn't matter how the PCM is getting Item #2, the air flow.... it uses the tables, and formulas to calculate a TARGET A/F RATIO

2 - The mass of air flowing into the engine in a given period of time

The PCM can get this number two ways...

2.A MAF PCM looks at the frequency signal from a MAF sensor, and converts that frequency signal to a "grams/second" value, using the MAF calibration table that has been stored in the PCM.

2.B S-D Does a calculation that requires:
-RPM (from the ignition system)
-engine displacement (programmed into the PCM)
-Volumetric efficiency (programmed into the PCM)
-inlet air temperature (from the IAT sensor)
-manifold absolute pressure (from the MAP sensor).

RPM/2 x displacement x VE = the VOLUME of air entering the engine.

Using the perfect gas law, IAT and MAP are used to calculate the DENSITY of the air entering the engine.

VOLUME x DENSITY = MASS

 

You forgot the injector constant. Or in some applications (only TBI?), it's called a BPC (base pulse constant) that incorporates cylinder displacement and injector size into one constant. The PCM/ECM has to know how much fuel will go in for a given pulse width!

If this is true, I would be very impressed. But everything I've learned so far about transient fuel demands (AE aka pump shot) says it's not about speeding up the PCM or placement of injectors, it's about what happens when you open the throttle. I think fuel is needed before the manifold pressure drops, regardless of how fast the PCM samples the MAP sensor. TPI cars, both MAF and the later S/D cars, have AE in their ECMs. Those are multiport EFI applications, though not sequential fire. The later S/D TPI cars use the 730 ECM which is arguably as powerful as the 8051 LT1 MAF PCM, and there is AE there. The mystery continues.
I did ask a friend of mine once where the AE tables were, and he said that since the LT1's MAF system was superior to the old TPI system (MAF output was a simple 0-5V output, like a MAP sensor, in those cars), the MAF could actually handle AE demands by just reading the airflow. And the PCM sampled the frequency output fast enough to make it work. This impressed me enough. But if this also works in S/D mode I will be REALLY impressed! How about 93 guys? Is there AE in those ECMs? There must be. Are you saying that if a 94-95 car gets a bunch of engine upgrades and the owner decides to run in S/D, gets VE dialed in, and spark dialed in, the car will run very well? That would imply that AE is, indeed, taken care of inherently by the PCM. Wow.

 

I didn't forget anything.... I was simply trying to clarify the points he was having trouble with.... he was not able to distinguish between one system that measured (or calculated) mass air flow, and another system that calculated the target A/F ratio. I explained how it got the mass fuel rate, so that it could calculate the pulse width. I was not discussing how you calculate the pulse width.

Not sure why you feel the need to undercut a discussion that had nothing to do with the point you posted..... but we're impressed with your in-depth knowledge and your willingness to share it with the unimfomed masses.

 

Ah, I misread your post. You're right, calculating airflow is different from calculating pulse width.