New to tuning, this here may not be the most correct way of doing things, but I`m a bit lost. I was wondering if you guys could help me out. Ive been trying to figure out how the ecu calculates the airflow, g/cyl, when there is no MAF sensor in vehicle.
This might help.
Snagged this from some reading material.
Speed-Density
Speed-density is one of the most common methods of load control and airflow calculations. This method uses an equation relating the manifold absolute pressure (MAP) and the intake air temperature with the known volumetric efficiency characteristics of the engine to calculate airflow, and thus makes it possible to calculate fueling requirements. While this method is not as robust and flexible as the MAF approach, it is not as sensitive to placement, errors and limitations in range, and in some applications can calculate airflow almost as accurately as a direct measurement. Speed-Density systems also have the benefit of not requiring an obtrusive sensor directly in the intake stream, as the MAF sensor can often actually impede airflow. The cost of implementation of such a system is also significantly cheaper. In speed-density systems the volumetric efficiency must be known and recorded in a reference table and will be used in air flow calculations. Using the universal gas law (PV = nRT) it is possible with the MAP, IAT and volume filled to calculate the mass of the air. This method is simple, but accurate. With the mass airflow now known fuel requirements can be calculated using the same equation used with the MAF method.
Speed-Density systems are very sensitive to temperature changes. As such, it is critical to pay close attention to temperature correction factors. This is due to changes in air density at differing ambient air temperatures (recall the VE and MAF equations use density at standard temperature and pressure.) Speed-Density systems also require more time to calibrate, as the entire V.E. table must be programmed into the ECM/PCM, and will be affected by engine component changes, especially parts that drastically change airflow behavior such as forced induction, cams and intake manifolds. Care should also be taken to ensure the VE map is as smooth as possible while maintaining adequate air/fuel ratios. An additional drawback with Speed-Density system can be a decrease in airflow resolution (sample rate) due to the calculation in lieu of direct measurement. Note that installation of forced induction or large increases in boost may also require the MAP sensor to be upgraded to a unit with a higher range.
2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.
If you don't post your tune and logs when you have questions you aren't helping yourself.
Thanks, for your response! I way too new to tuning, might seem like dumb question. Here goes.... Speed density method is done by the ecm?
If you tell it to, yes.
From the factory they use dynamic airflow to run these LS motors. It uses both the MAF sensor and the MAP sensor to make airflow calculations and fueling calculations. If you remove the MAF sensor from the vehicle you need to tell the computer that.
You would disable the MAF sensor by settings the MAF fail High HZ to 0hz under ENGINE DIAG tab, then set the 3 MAF dtc's to fail on first error. You also have to wire in a seperate IAT (intake air temp) sensor if your vehicle has it built into the 5 wire MAF sensor harness.
2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.
If you don't post your tune and logs when you have questions you aren't helping yourself.
Im a bit slow, sorry. So without the MAF how would the ECM calculate the grams/cylinder.
With math.
You can make your own graphs to log it whatever way you need too. Like the spark tables in rpm and cylinder airmass. You could create a graph and log it exactly like that.
2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.
If you don't post your tune and logs when you have questions you aren't helping yourself.
Another question....
What is or what does it do.....
Under Engine Diagnostic> Airflow tab> Throttle Position Sensor> Calc Airmass - P1514/P0068 Error button do
It brings up a screen/map labeled [ECM] 14040 - Calculated Airmass vs. TPS vs. RPM- P1514 Error
By the way, Im not to engine savvy, Im the translator, so I maybe losing some in the process. So how does the engine know how much air its going in with no MAF sensor telling it
How or where would i calculate and figure such graph and input in the ecm
It uses speed density to figure out how much air is going in, aka the MAP sensor. Along with the intake air temp to calculate how much is coming in.
I suggest lots of reading and researching things. Buy some books to help you understand how various sensors work and functions. Read the VCM scanner section for helpful hints of how to setup the graphs for logging.
Can't really spoon feed this stuff, gotta put in the homework to figure it out.
2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.
If you don't post your tune and logs when you have questions you aren't helping yourself.
A simplified explanation. With a Gen 3 PCM it uses a Volumetric Efficiency table which is a X-Y Axis table with one axis being RPM and the other axis MAP values. For each unique MAP Value and RPM value in that table there will be a cell where that row and column intersect. A numerical value in that cell represents an air mass for those MAP/RPM values. Your air mass model will only be as good as the accurate populating of that VE table. There are adjustments to that table based on coolant temp and intake air temp the PCM makes but it starts with the values in the VE table.Originally Posted by gvilla
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