Blocking of EGR's

I, personally would like to thank all of the discussion on EGR's. I blocked mine off on the weekend and can not believe the difference it has made. I too was listening to the pro's and con's and the only con's that I heard were the legalities (obviously) and the fact that the EGR is used to lower combustion temperatures? This second point to me does not make much sense. The engine can only take so much air, so surely the intake temperature to the cylinder would be lower if it was 100% 'virgin' air rather than 80% virgin + 20% hot exhaust, (or whatever the ratio be) so for me this nulafied the second con.
I did the change and these are my results,
Idle is now smooth, it does not hiccup every 5 seconds or so as it used too.
Flat spot at about 800 rpm is now gone
Usable torque is now available from 1500 rpm as opposed to 1800-2000 as before
Flat spot at about 3300 rpm is gone
Engine feels as if it is less restricted, ie boost now comes on smoothly and more rapidly.

Not sure yet as to the impact on economy, however even if it uses a little more fule, the 3L is quite good on fuel anyway and it would not bother me if it used slightly more.

Mine has not had a d-tronic or such fitted, we also blocked off a mates EGR yesterday and had nearly identical results, his does have a d-tronic.

Again, very happy with the results.

The temperature goes down because you are taking away the input of hot air from the exhaust. Its not rocket science.

It would also increase the power a bit as cold oxygenated air has a better combustion efficiency than warm gas that has an oxygen defficiency.

Have you ever noticed that when you drive a car on a cold, frosty or foggy night that the power and torque are noticably higher. That is one of teh reasons that trucks do long trips at night. They pull better.

thats the point I was trying to make!
i was trying to understand how injecting hot air from the exhaust could possably have a cooling effect on combustion temperatures as had been mentioned previously!

Hi Guys,

There is a little bit of confusion regarding EGR temperatures amd engine combustion temperature. I hope the following helps.

Yes, EGR is hotter than intake air however remains significantly cooler than peak combustion temps. It is the latter, with excess O2, that leads to the formation of NOx which is not desirable due to impact on respiratory diseases and cancer. So what on earth does EGR do then? The effect is two fold 1) EGR is inert and therefore displaces oxygen which reduces the excess oxygen, 2) the peak combustion temperatures are lowered due slower combustion rate. The latter is also controlled by fuel timing (akin to ignition timing), in-cylinder air flow control, etc. This is why the introduction of hotter exhaust gas results in lower combustion temps.

On modern diesels, electronic engine control of the combustion process allows for very high levels of external EGR to be metered via the EGR valve. It is not the temperature of the gas but the mass of EGR that leads to NOx reduction. In a similar way that cold intake air makes more power (i.e. greater mass O2), so too for EGR. This is why later generation diesels run EGR coolers - not to reduce EGR temp for engine life but to get more exhaust gas back into the cylinder and allow for greater NOx reduction.

EGR does not come without problems. Increasing EGR at part load conditions negatively impacts combustion stability, hence the need for modern electronic controls to make the appropriate timing adjusments (based on how the engine has been calibrated by the OEM). EGR also increases the soot loading and levels of nitric acid, both of which have required advances in engine oil technology. Running without EGR is certainly easier on the base engine, but not too good for the environment and public health (a matter of conscience I guess).

The ZD30 is calibrated for very high levels of EGR (~ 50% in some cases). The engine calibration will have been developed on this basis, with fuelling rates, timing, boost control, swirl control, etc based on an assumed level of mass EGR. Unlike early systems where EGR was metered by valve position setpoint, modern engines run mass EGR control, with feedback based on volumetic efficiency model using manifold pressure and temperature as I/O. The EGR valve simply modulates to provide the EGR mass flow called up by the calibration (for a given speed/load).

I don't know how the ZD30 engine has been mapped for no EGR case, however this will have been taken into consideration. The fact that guys are getting good performance with the EGR circuit blocked is an indication that the calibration has taken this into account to some degree. Whether or not this has been fully validated for engine durability, fuel economy, etc is questionable but I wouldn't expect it to lead to engine seizure. In a similar fashion, I also don't think that EGR valve failures lead to engine seizure either - unless the valve failed in the fully open position (and then I'd expect you'd get an engine warning light almost immediately and the engine run quality would be crap). There certainly have been EGR valve failures but from what I've read the engine runs OK once replaced.

I did a search on ZD30 EGR last night and attached links may be good reading for some.

ZD30 article

EGR basics

EGR effect on oil

Best regards,
Hugh

It does reduce emissions. Certain pollutants only form at higher combustion temperatures. By introducing exhaust gas, those temperatures are reduced.
Whether there are other benefits by feeding exhaust gas and soot back into the intake is very debatable.......

All the calibrations have been set up based on the EGR working correctly, so you will have it running lean with EGR not working.

That would be true for a petrol engine...
cheers

From suggestions above, I suppose we need to find out if the ECU backs the fuel off when it tells the EGR valve to open. From what I have read so far, this may be the case with the 3.0, as it was sugested that it has a servo motor that opens the valve in varying amounts, but the 2.8 seems to have a vacuum operated on/off valve (I believe the later model 4.2's have this as well.) Anyone know whether the fuel mix is adjusted by the ECU?

Chers Andrew

Hi,

I am sure the ECU does alter something else as it increases EGR, maybe injection timing and fuel quantity or both. It is not a problem if it injects less. Diesels run very lean anyway. Of concern would be if it increased fueling, but that would almost certainly show up as an increase in black smoke. It does not do that. The other issue is boost pressure. As there is more exhaust gas going into the turbo now, it is bound to spin up more. In another threat, someone with a boost guge did mention that it comes on faster with the valve blocked, but does not seem to get higher as before. He also mentioned that exhaust gas temperatures were lower with the valve blocked, which does suggest it runs leaner.
Anyway, it seems to be a very common thing done. My experience in driving with it for one tank full.... There is lots more torque in mid range 1500-2500. Fuel usage is down also, but not that much, perhaps 1/2 to 1l/100. Idle is not shaky any more.
So, contemplating whether to do it permanently.....
Cheers

Maybe with the more exhaust pressure, the turbo winds up quicker, but the pressure does not get as high on the inlet side as the exhaust gas going into the inlet manifold via the EGR is under pressure so will give a higher reading on the boost guage. I'm not sure, but its a good discussion though. mine is now blocked (vacuum hose) and I have noticed no difference.

Cheers Andrew

I'm not sure. From what I have been told blocking the vacuum line will do, and it is very quick. I may pull mine apart this week just to confirm that the vacuum opens, not closes the valve.

Cheers Andrew

I'll block it this arvo and try it out to see if there is any difference.

All I did on the surf was remove the vacume hose, put some silicone in both ends , let it dry and re connected it. No one would ever know anything was ever done to it and it stopped it smoking under acceleration immediatly.