EGR Mod: Best thing you can do - Here's why!

[xtturbo]

Ok,

While I'm not the first to post about the EGR mod (my car is a YD25), I do know a thing or two about engines so I thought i'd post my experiences.

Today I made up a blanking plate - i mounted it on the left right next to the EGR control valve / just after the exhaust cooler pipe. Why? Because its the easiest to get to, and location should make little difference if any.

Result: Engine is a whole lot nicer before boost kicks in. This is basically because the EGR is open at idle and part throttle.

Because the EGR is now blocked off, the entire intake system is no longer being filled with exhaust gas while you idle, and the engine doesn't have to suck it all down when you try and take off at part throttle.

Some stats (taken from OBD-2 Port with Diag Tool):

Without EGR Mod:
~11 grams / second of air consumed at idle
~30 degree intake temps

With EGR Mod:
~16 grams / second of air consumed at idle
~20 degree intake temps

Basically, this means at idle, without the EGR mod, roughly 30% of the air going into your engine is exhaust fumes... No wonder it hesitates!

Additionally, the air is now cooler and hence denser, and more fuel can be burnt, more efficiently!

Cheers,

xtturbo

 

[the_bluester]

I have never been too keen to go doing the EGR mod seeing that the boost control seems to be open loop and on the VNT version that can lead to some odd problems. I have wondered about making a restrictor plate for it though to get part of the response benefit while hopefully not leading to boost control issues.

 

[Jason]

Good info xtturbo!

 

[justAL]

Very good info. It's great to have the figures and to help explain to those with less mechanical knowledge.

 

[ST-R]

I have never been too keen to go doing the EGR mod seeing that the boost control seems to be open loop and on the VNT version that can lead to some odd problems. I have wondered about making a restrictor plate for it though to get part of the response benefit while hopefully not leading to boost control issues.

Can you explain what you mean by open loop please?

Regards

Greg

 

[tweak'e]

Basically, this means at idle, without the EGR mod, roughly 30% of the air going into your engine is exhaust fumes... No wonder it hesitates!

i'm a little surprised that the EGR is open at idle.
i didn't think that the 2.5 D22 had an egr butterfly, so it would need some exhaust back pressure to be able to shove that amount of EGR in, which you don't normally get at idle.

are you sure your reading the gauge right? in particular thats its true mass reading ie that temp is already compensated for?

edit: just looked up the manual and it looks like EGR is open at idle. i forgot about the egr cooler which increases the amount of EGR for the amount of pressure difference.

 

[xtturbo]

i'm a little surprised that the EGR is open at idle.
i didn't think that the 2.5 D22 had an egr butterfly, so it would need some exhaust back pressure to be able to shove that amount of EGR in, which you don't normally get at idle.

are you sure your reading the gauge right? in particular thats its true mass reading ie that temp is already compensated for?

edit: just looked up the manual and it looks like EGR is open at idle. i forgot about the egr cooler which increases the amount of EGR for the amount of pressure difference.

I was reading some research papers on EGR systems on diesels, apparently it is quite common to apply as much as 30% recirculated gas. EGR is actually really effective, and can lower NOx emissions to 0%, which is pretty amazing.

But heres the bad news. The only reason the EGR isn't always on is the technology to control it properly under boost conditions etc isn't fully developed yet. All the research papers hint at this being the next big thing in diesel emissions technology, due to the low cost and effectiveness of EGT systems.

In other words, don't hold your breath, because the next generation of diesel engines will have continuous EGT. Hopefully they tune them a little better than they have in the "crippled" D22 YD25. (As the D40 YD25 has a VNT, it is quite possible EGT is not as big a factor).

Btw, as EGT takes the exhaust gases before the turbocharger, both spool times and the rpm needed to spool the turbo are increased. Blanking the EGT will deliver quicker turbo spool, resulting in less lag, lower spool rpms and obviously greater efficiency.

Disclaimer: By blocking off the EGR, you're helping cause acid raid, but you'll slow down the depletion of oil reserves... Whats the environmentally ethical position? Who knows.

 

[tweak'e]

By blocking off the EGR, you're helping cause acid raid, but you'll slow down the depletion of oil reserves... Whats the environmentally ethical position?

LOL love it

yes egr is generally in the 30-50% range. with hot egr you only get up to about 30%. cooled EGR (what the 2.5 has) can go as high as 50%.
trouble is soot and other emssions skyrocket up after about 20%. hence the need to clean up the exhaust with cat and dpf's.

i'm not sure what you mean by they don't have the tech to control it properly under boost conditions. controlling it is not really all that hard. one problem is system lag, which is why pre turbo EGR is generally favoured compared to after turbo/cat/dpf.
the thing that is coming up is measuring and controlling blowby gases ie the breather system. thats effectively EGR and at present its unmeasured, so thay have a bit of head room in case you get a lot of blowby.

continuous EGT ?? or continuous EGR ? continuous EGR is what these engines have. ie variable control compared to the old on/off style valves they used to run.

 

[the_bluester]

Can you explain what you mean by open loop please?

Regards

Greg

In reference to electronic boost control. I will explain it for a normal turbo as it is simpler to explain than for the VNT. On a D22 ZD30 they simply fit a boost line from the compressor side of the turbo to the wastegate actuator, when pressure rises far enough, the actuator opens a bypass valve that diverts exhaust gas around the turbine to slow it and regulate boost. Electronic boost control puts a solenoid in the line that is operated in an on/off mode, usually at about 30 cycles a second, when on the solenoid bleeds air off the pressure line to the wastegate actuator, making it see a lower pressure than is actually being produced by the turbo and keeping it closed, that increases the boost level. The ratio between the on and the off (Duty cycle) essentially bleeds more or less air off the wastegate to set a higher or lower boost pressure.

Open loop gives you that for X rpm and Y throttle position, the solenoid is given a signal of Z duty cycle. That will produce an average boost level that the factory accepts as OK.

Closed loop monitors the actual boost pressure and varies the duty cycle to try to produce a specific target boost at whatever condition the engine is currently in.

If you change significant things like fit a free flowing exhaust with open loop then the ECU continues applying the same duty cycle as before and your boost level can be quite different to what was intended. ZD30 powered Patrols appear to need significant mods when people fit EGR blocking plates as they have boost control (A ZD30 Nav does not and I do not think the YD25 powered D22 does either, but a D40 does have it) When people block the EGR in a Patrol they can end up with real boost spiking and other control problems.

The problem with closed loop control is that it can be really tricky to set up and make work right. I run open loop boost control on my track car, I fiddled with closed loop for many hours before abandoning it as I could not get it to be responsive and free of boost spikes when you snap the throttle open without having boost fluctuations at part throttle.

 

[xtturbo]

LOL love it

yes egr is generally in the 30-50% range. with hot egr you only get up to about 30%. cooled EGR (what the 2.5 has) can go as high as 50%.
trouble is soot and other emssions skyrocket up after about 20%. hence the need to clean up the exhaust with cat and dpf's.

i'm not sure what you mean by they don't have the tech to control it properly under boost conditions. controlling it is not really all that hard. one problem is system lag, which is why pre turbo EGR is generally favoured compared to after turbo/cat/dpf.
the thing that is coming up is measuring and controlling blowby gases ie the breather system. thats effectively EGR and at present its unmeasured, so thay have a bit of head room in case you get a lot of blowby.

continuous EGT ?? or continuous EGR ? continuous EGR is what these engines have. ie variable control compared to the old on/off style valves they used to run.

* Continuous EGR

pre turbo is all fine and dandy, but once the engine comes on boost its unable to run any EGR at all (the intake is now pressurized, remember).

Newer systems aim to come up with ways of introducing EGR all the time, including boost conditions.

 

[Old.Tony]

* Continuous EGR

pre turbo is all fine and dandy, but once the engine comes on boost its unable to run any EGR at all (the intake is now pressurized, remember).

Newer systems aim to come up with ways of introducing EGR all the time, including boost conditions.

They'll make the damn things so inefficient we'll be pouring ten times the fuel into the engine. What's the point?

I suppose if we run out of fuel faster, we'll all move to electric vehicles quicker. Plus, every litre of diesel we buy puts $$ into the mega-corporates' stash. They have a vested interest in us wasting fuel!

 

[the_bluester]

I thought one of the things under investigation was using new generation turbos to replace some EGR. The whole point of EGR is to effectively pollute the combustion process to reduce temperatures and therefor NOX emissions.

New VNT turbos would be capable of producing high boost pressures in cruise conditions, effectively reducing combustion temperatures by leaning off the mixture due to excess air. I would far rather see a car that tools around running 20PSi to increase airflow and reduce combustion temps rather than by recirculating exhaust gas. It would all depend on if they could build a turbo that would provide the performance at full noise while not going into compressor surge when running at high boost/low load conditions.

 

[tweak'e]

* Continuous EGR

pre turbo is all fine and dandy, but once the engine comes on boost its unable to run any EGR at all (the intake is now pressurized, remember).

Newer systems aim to come up with ways of introducing EGR all the time, including boost conditions.

i think your out of date a bit, they all have EGR flow on boost.

exhaust back pressure always exceeds boost. to increase flow they can either restrict intake flow (reduce pressure) with a inlet butterfly (ie egr butterfly) tho most engines theses days use a variable turbo to do it. it closes the vanes to block off the exhaust to increase back pressure which keeps the pressure above boost pressure. all controlled by measuring mass air flow and position of turbo vanes and egr valve.

very few vehicles run boost higher than back pressure.

 

[tweak'e]

I thought one of the things under investigation was using new generation turbos to replace some EGR. The whole point of EGR is to effectively pollute the combustion process to reduce temperatures and therefor NOX emissions.

New VNT turbos would be capable of producing high boost pressures in cruise conditions, effectively reducing combustion temperatures by leaning off the mixture due to excess air. I would far rather see a car that tools around running 20PSi to increase airflow and reduce combustion temps rather than by recirculating exhaust gas. It would all depend on if they could build a turbo that would provide the performance at full noise while not going into compressor surge when running at high boost/low load conditions.

i think thats a little bit out.

high boost doesn't reduce NOx nor does it reduce combustion temp thats responsible for making NOx.
high boost reduces EGT's, ie the average combustion temp. NOx is formed by PEAK combustion temps. EGR reduces peak temps but tends (but not always) increase average temps.

i understand some current VNT equiped diesels can run constant boost almost from idle. the big problem is efficiency. variable turbo's tend to have a wide operating range but are not as efficient.

 

[xtturbo]

i think your out of date a bit, they all have EGR flow on boost.

exhaust back pressure always exceeds boost. to increase flow they can either restrict intake flow (reduce pressure) with a inlet butterfly (ie egr butterfly) tho most engines theses days use a variable turbo to do it. it closes the vanes to block off the exhaust to increase back pressure which keeps the pressure above boost pressure. all controlled by measuring mass air flow and position of turbo vanes and egr valve.

very few vehicles run boost higher than back pressure.

D22 doesn't have a VNT / VGT

But yes, its possible these days with newer turbos.

 

[tweak'e]

exhaust back pressure pushing EGR in is how all short path EGR systems have worked. doesn't matter what age it is.

 

[xtturbo]

exhaust back pressure pushing EGR in is how all short path EGR systems have worked. doesn't matter what age it is.

Sure, but the YD25 D22 doesn't run EGR under boost conditions.

 

[tweak'e]

Sure, but the YD25 D22 doesn't run EGR under boost conditions.

yes it does. it would fail EURO standards if it didn't.
of the top of my head the manual says it doesn't run EGR when at full throttle or when cold or overheating. otherwise EGR is on regardless of boost.

 

[Jason]

From the service manual:

The EGR volume control valve remains close under the following conditions.
• Engine stopped
• Engine starting
• Low engine coolant temperature
• Excessively high engine coolant temperature
• High engine speed
• Accelerator pedal fully depressed

The manual also gives the following system description:

This system controls the flow rate of EGR led from exhaust manifold to intake manifold. The opening of the
EGR passage in the EGR volume control valve changes to control the EGR flow rate. A built-in DC motor
moves the valve continuously corresponding to the ECM output signal. The EGR volume control valve control
position sensor detects the valve position and sends the voltage signals to the ECM. The ECM judges the current
opening angle of the valve from this signals and the ECM controls the DC motor to make the valve opening
angle properly.
The opening of the valve varies for optimum engine control. The optimum value stored in the ECM is determined
by considering various engine conditions.

 

[Old.Tony]

^ and that feedback to the ECM is the reason why you can't just unplug the ruddy thing.

They do the same with the Heated Oxygen Sensor (exhaust) and God knows how many other things too.