CHessMaster wrote:
It doesn't monitor the flow through the EGR valve per se, it looks for a drop in air flow at the mass airflow sensor (right by the air filter box) when the EGR valve is open, and assumes that loss in flow is due to exhaust gas being rerouted back into the intake manifold. If you pipe compressed air from the turbo outlet to the exhaust side of the EGR valve, that air has already passed through the MAF sensor and won't be causing the reduction in flow at the MAF sensor during EGR valve operation that the PCM is expecting. Long story short, this won't prevent an insufficient EGR flow any more than just blocking off the EGR valve, since either situation results in the same amount of airflow at the MAF sensor.[/quote]
This is correct.
Put another way:
When the PCM commands the EGR to open via PWM (Pulse Width Modulation) it knows that (for example) 50% of EGR open time equals "X" amount of air flow displaced from the fresh air intake system (since it comes from the exhaust system instead of through the air filter). The PCM must see this corresponding drop in fresh air via monitoring the MAF sensor output. If the 2 are equal (within a set parameter), the PCM assumes that the EGR system is working.
So; to do a EGR "bypass", you would need to plumb the EGR system so that when the EGR valve opened, instead of getting exhaust gasses, you let fresh filtered air through the EGR valve (from anywhere except AFTER the MAF sensor). This would satisfy the above conditions for the PCM and would not turn on any EGR related code(s).[/quote]
Ah! This is the kind of information I was looking for. So no, my original concept won't work. It would take airflow not accounted for by the MAF.
By the way, I am an automotive engineer. But, I'm not in powertrain or emmisions. I'm in dynamics and kind of subscribe to Carrol Smith's views on engines. That is, untill I have to put money into them. I'll delve into the DIY tunes now.
Thanks to everyone for the input!