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Discussion and questions related to the course Practical Diesel Tuning
I'd like to reduce the EGRs opening during cruising speed hopefully to extend the range of DPF regen cycle.
There are total of 3 different EGR tables(see attached) and I'm thinking to adjust the EGR from 1,600 RPM onwards. However, I'm wondering what other tables should be adjusted to compensate for this change.
You may notice that your feed forward vane position tables feel a little aggressive after after adjusting EGR but if it were me I'd wait to modify them until I logged vane position against 'desired vane position' and got a sense of the gap between these things. Simple answer is 'nothing to start with'.
I'm not even sure where to start :) what exactly is feed forward vane position?
The engine will be looking for more fresh air when I make changes to the EGR table by limiting/reducing the amount of recirculated air, is that correct?
Does the ECU know how to compensate for this or I'll get in trouble by hurting and possibly damage the engine?
I've attached all available maps by classes. Please advise if there's anything specific I'll need to look into.
Feed forward is another way of saying 'desired'. It's the starting point of the turbo vanes at a specific load and rpm, from there the engine may adjust vane position to reach a desired airflow or boost.
If you reduce the EGR fraction the engine will no longer need to use higher vane position settings. Higher vane position is used to create difference in pressure between the exhaust and intake tract and thus entice the exhaust gas to actively flow from the exhaust manifold back into the intake. Adjusting nothing but the EGR fraction will not cause any problems with the engine. You can easily do this and drive the car. What you may notice is that now your combustion is more lean than necessary because the high vane position settings required to make the EGR function properly are causing higher 'fresh airflow' numbers as a result of the restricted the EGR orifice caused by your EGR table edits.
Nick, thanks for the detailed explanation, it helps :) I coded the egr cooler valve to remain closed while not modifying the cooler bypass valve tables so it remains operational. After that, it threw a DTC saying insufficient flow which is expected. Will this cause any harm to my engine?
I do not have a history of tuning your engine variant so I can only speak in theory. In general, running more or less EGR is not going to damage an engine quickly. Running excessive EGR will degrade parts over thousands of miles. Running too little will cause NOx levels to soar and make passing emissions difficult.
The bypass system is designed to get hot EGR when the engine is cold and then switch to cooled EGR when the system warms up. I don't know that I like your idea of closing the cooler valve. I cannot tell if you limiting coolant flow or EGR flow. If you're limiting coolant flow you're asking for trouble or a cracked cooler. If you're limiting the flow of cooled EGR, there's no risk of parts failure.