Thread: EGR

Originally Posted by Dougal

There is nothing pedantic about correcting those applying petrol engine theory to diesels.

How exactly do you disagree with the fuel cut?
The fuel use display in your own vehicles will show a big 0.0 litres/100km whenever you lift off.

Pardon my ignorance but from what you have said there is no (zero) fuel going into the combustion chamber when the throttle is closed, then I'll ask the obvious, how does a diesel engine idle at a stand still if the fuel is cut off completly when the throttle is closed?

Not trying to be a smartarse but the question needed to be asked given the various comments.

No fuel is supplied at zero throttle when the revs are over idle revs.

Originally Posted by TerryO

Pardon my ignorance but from what you have said there is no (zero) fuel going into the combustion chamber when the throttle is closed, then I'll ask the obvious, how does a diesel engine idle at a stand still if the fuel is cut off completly when the throttle is closed?

Not trying to be a smartarse but the question needed to be asked given the various comments.

How can you not be trolling?

For a start, there is no throttle to close. Diesels are controlled on fuel alone. If the actual rpm is higher than the requested rpm, then fuel is reduced or cut completely. This continues until the requested speed is reached.
Same thing when the requested speed is idle speed.

Having just done this to my TD6, I find the change in vehicle performance incredible. Firstly it has dropped the auto box lock up point from 80k/h to 55k/h and it will actual pull with gentle throttle in top although it will kick back when required. Now it drops back to 4th gear instead of 3rd, which means I am now getting better fuel consumption. As to an explanation as to why this happens.
In laymans terms (and correct me if I am wrong), totally clean air at a far lower temperature as after blanking would have a higher oxygen level so there would be better fuel burning at a slightly higher compression (cold air) as the air is more dense than if zero oxygenated fumes at high temp. are added to the air intake. Jim

Originally Posted by jx2mad

Having just done this to my TD6, I find the change in vehicle performance incredible. Firstly it has dropped the auto box lock up point from 80k/h to 55k/h and it will actual pull with gentle throttle in top although it will kick back when required. Now it drops back to 4th gear instead of 3rd, which means I am now getting better fuel consumption. As to an explanation as to why this happens.
In laymans terms (and correct me if I am wrong), totally clean air at a far lower temperature as after blanking would have a higher oxygen level so there would be better fuel burning at a slightly higher compression (cold air) as the air is more dense than if zero oxygenated fumes at high temp. are added to the air intake. Jim

For the shift points to change, a sensor is now reading a lot different to what it was previously.
That is driving your differences. Conditions in cylinder don't alter shift points.

Did you get EGR mapped out or just blanked?

On a side note, something to look forward to in the future, a second EGR taking exhaust from down stream of the DPF to try to combat the sooting problem. This is going to be slow in operation so the first one will still be needed. Who ever invented the EGR system should hang their head in shame.

Originally Posted by Dougal

How can you not be trolling?

For a start, there is no throttle to close. Diesels are controlled on fuel alone. If the actual rpm is higher than the requested rpm, then fuel is reduced or cut completely. This continues until the requested speed is reached.
Same thing when the requested speed is idle speed.

Actually that's not strictly true.....some diesels do have throttle plates. The tdv8 has 2 throttle plates in the throttle bodies but it is very rare.
But you are still 100% correct that a diesel in controlled on fuelling.

Originally Posted by fonfe

Actually that's not strictly true.....some diesels do have throttle plates. The tdv8 has 2 throttle plates in the throttle bodies but it is very rare.
But you are still 100% correct that a diesel in controlled on fuelling.

They are for EGR flow and quiet shut-down. They might look like a conventional throttle, but they don't work in any way the same.