EGR DC % - how does the PCM calculate?

[Craig 94 TA GT]

With my high NOx problem, I did a scan to see my EGR DC %. It looks like it is functioning - under certain circumstances, it will quickly hit 12.5, then 0, then 12.5 - continually switching. Then at other times, it just sits at 0.

That part seems to look normal, but I was wondering what feedback the PCM uses to calculate how much to open the EGR? I know it doesn't know what the EGR is actually at, just sends the command. But, what tells the PCM to open it that much? It can't possibly tell high combustion temps and open the EGR right?

[Injuneer]

I don't know the answer, but suspect it looks at combinations of MAP, RPM and TPS that would indicate the engine ie being "lugged" at low RPM/moderate to high load. That's what would cause high combustion temps. It may also factor in coolant and inlet air temps.

[Rob B (shoebox)]

Fred pretty much has it.

This is from my website:

EGR Control
Vacuum to the EGR valve is controlled by a solenoid valve that is pulse width modulated by the PCM. This modulation of ON and OFF many times per second controls the amount of time vacuum is applied to the EGR valve.

The PCM uses RPM and info from the following sensors to regulate the valve:

Engine Coolant Temperature (ECT) sensor
Intake Air Temperature (IAT) sensor
Throttle Position Sensor (TPS)
Manifold Absolute Pressure (MAP) sensor
Park/Neutral Position (PNP) switch
Vehicle Speed Sensor (VSS)

[FTA1995]

I remember from last year I believe Craig I looked into your .lt1 file with you so I know you've done some tuning. I don't think there are provisions in tunercat for making adjustments to pulse width duration or dynamics off the top of my head, but did you ever change anything in the table that modifies timing when the egr solenoid is running a commanded cycle? I know you have to keep to a rather stringent emissions profile in your region; maybe this table could help your nox count by giving a few degrees + or -...

Just figured I'd bounce the idea, your carbon number might go up a tad.