Need help, stumped on timing

[JP_z71]

Cannot figure out why commanded timing isnt the actual timing, no egr, no engine TM, its not IAT or ECT, but still doesnt actually put in the commanded timing value. '06 silverado 1500 5.3 all stock but unplugged maf. Preciate any advice

[JP_z71]

And transgo vette servo

[smokestack]

There's a lot of timing adders/subtractors to look at.

[mowton]

Remove the MAF PID from your Chart display. By unplugging MAF you have failed over to SD and the MAF at 0 will affect the g/cyl calculation. It'll line right up when you do that. If you plug the maf back in, then bring in MAF PID again. You can just check or uncheck the enable box.

Ed M

[JP_z71]

yeah that were my intentions with unplugging it. Just removed the MAF PID in chart display.

[mowton]

yeah that were my intentions with unplugging it. Just removed the MAF PID in chart display.

and......?

Ed M

[JP_z71]

sorry man, this is a log after i did it, and just started runnin 93

[JP_z71]

ive looked at the IAT,ECT and AFR adders and its not them, but still not doing the commanded timing from main spark table

[JP_z71]

and i apologize for my inexperience but i definitely want to learn, so what exactly did deleting the maf pid from the chart fix?

[mowton]

and i apologize for my inexperience but i definitely want to learn, so what exactly did deleting the maf pid from the chart fix?

I worked on several tunes today and must of gotten yours mixed up with another, because I thought you were logging Dynamic Airflow. With the MAF plugged in, the PCM calculates the cylinder airmass (g/cyl) based on the MAF Airflow value, RPM and the number of cylinders. a few filters and adjustments are incorporated to arrive at the final g/cyl value or how much air is actually making it into the cylinder. The PCM doesn't use just the MAF value, its looks at the VE and compares the 2 to determine reasonablness and based on its decisions creates an adjusted Airflow parameter called Dynamic Airflow. It can be either pure MAF (steady state) or biased to the VE, depending on the severity of any mismatch (transient state) conditions or worse yet a MAF failure. This is the actual value the PCM uses to develop the cylinder airmass value for fueling, spark table selection etc.

When you disconnect the MAF, you create a MAF fail as you stated, and the PCM then biases the Dynamic Airflow to the VE table as it is the only means by which it can calculate the cylinder airmass. As you can see, the Calc Cyl Air PID displays 0 with the MAF unplugged because it is a PID developed purely from the MAF PID. To create the same calculated airmass PID to show the SD value, you need to log Dynamic Airflow and develop the following custom PID in the User Defined>Configure User Defined section (you will find the MAF based Calc Cyl Air there also). Here is the PID where [PID.2320.MET]*(120/[HPT.NUM_CYL])/[PID.12]. Dynamic Airflow = [PID.2320.MET], factor and number of cylinders is (120/[HPT.NUM_CYL]) and RPM = [PID.12]. This is how the PCM is accessing the spark table and the commanded spark will now equal what you are seeing.

So to make sure things line up you would also delete the MAF PID from the table and chart display.

Not sure if I did a good job explaining this....hope so, if not ask away.

Ed M

[JP_z71]

ok found the config user define, so this "[PID.2320.MET]*(120/[HPT.NUM_CYL])/[PID.12]" is the funtion string

[mowton]

ok found the config user define, so this "[PID.2320.MET]*(120/[HPT.NUM_CYL])/[PID.12]" is the funtion string

Yes

Ed M

[JP_z71]

Alright made the pid but when i start scanning it says unsupported paramater

[mowton]

Alright made the pid but when i start scanning it says unsupported paramater

Make sure you have inserted Dynamic Airflow into your table display. Also make sure that your dynamic Airflow PID is 2320.

Ed M

[JP_z71]

Screenshot (1).pngScreenshot (2).png
it shows it when i dont have a log in it but when i start scanning it does that

[JP_z71]

Screenshot (3).png
This is the user defined parameter that i did

[mowton]

OK, I see what you did. So you created the user defined PID correctly and called it Dynamic Airflow, its really Dynamic cylinder airflow (DCA). You need to go to your table display, close the log, iright click nsert, and bring in the Dynamic Airflow PID which is PID.2320 as well as your user defined PID.

Ed M

[JP_z71]

awesome now i see what u were sayin with the g/cyl not lining up right, that fixed it
so now i wanna to understand why i did what i did
i understand with the maf gone it sends it into sd mode
so on the scanner the calculated cylinder airmass worked straight from the maf
without it then the cca was drawing a blank
so i made a pid that would log dynamic cylinder airflow based off of dynamic airflow*number of cylinders/rpm
and because the spark table uses cca to figure out where the motor is to log spark advance it messed the histogram up without cca
so because i now have the new dca pid the spark table now knows the correct g/cyl value to log timing
is that correct?

[mowton]

Wow, 9 lines of typing and not 1 period.....J/K

The PCM is always calculating Dynamic Airflow (DAF) to determine the total airmass ingested and adjusted for non-steady state events like say a gas pedal stomp. It then "favors" the VE settings because it always believes they are correct for non-steady state fueling because the OEM Engineers took 1000's of hours to develop those tables. From the DAF, the PCM then must calculate the amount of air actually being drawn into the cylinder so it calculates what I called Dynamic Cylinder Air (DCA). Again based on this value, the commanded AFR and a few other factors, it calculates the Injector Pulse width again based on your Injector Flow Rate and MAP/Delta Pressure. The spark table is indexed by that value as well as RPM and from there the PCM picks up the commanded spark value.

Even with the MAF plugged in, the Cylinder Airmass and Calculated Cylinder airmass aren't 100% correct (its close except in non-steady state events or, as you have seen, during MAF failures), only the DCA which we just created will correctly tell you the cylinder mixture and spark values.

Ed M

[JP_z71]

Now when you refer to the computer favoring the VE settings, i take it your not just talking about the VE table but other settings too?