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Discussion Starter · #9 ·
I remember the early days of VW TDI engines when you could use VAG-COM software to turn down the EGR flow to where it was minimal. It wouldn't trigger a CEL and the flow was so low that the intakes of the engine would never clog up.
 

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I remember the early days of VW TDI engines when you could use VAG-COM software to turn down the EGR flow to where it was minimal. It wouldn't trigger a CEL and the flow was so low that the intakes of the engine would never clog up.
You can do this in Gretio but it only works so as long as the phone is hooked up.

The problem is the ECM doesn’t quite adjust correctly. It’s not really a big deal but EGTs lower significantly and this can cause sound problems warming up. Without the EGR the engine needs to run hotter to accommodate but the stock calibration just doesn’t do that.
 

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Discussion Starter · #11 ·
this can cause sound problems warming up
You mean like sharp Diesel clatter in cold ambient temperatures?

That's not an unexpected side effect. The EGR cooler bypass is there to feed more of that hot exhaust gas into the intake during cold starts. You want hotter intake air so you can get reliable, stable combustion when the fresh air intake temperature is cold.

It's a similar trick that Mazda uses in their Skyactiv-D engines with 14:1 compression ratios - the variable valve timing keeps the exhaust valve open a bit after the exhaust stroke so the intake stroke sucks some of that hot exhaust gas back into the cylinder to mix with the fresh air intake charge. It raises temperatures to get those cylinders lighting off better when it's cold.

We used to just have 21:1 compression ratios and those engines could crank and fire in almost any temperatures without glow plugs!
 

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You mean like sharp Diesel clatter in cold ambient temperatures?

That's not an unexpected side effect. The EGR cooler bypass is there to feed more of that hot exhaust gas into the intake during cold starts. You want hotter intake air so you can get reliable, stable combustion when the fresh air intake temperature is cold.

It's a similar trick that Mazda uses in their Skyactiv-D engines with 14:1 compression ratios - the variable valve timing keeps the exhaust valve open a bit after the exhaust stroke so the intake stroke sucks some of that hot exhaust gas back into the cylinder to mix with the fresh air intake charge. It raises temperatures to get those cylinders lighting off better when it's cold.

We used to just have 21:1 compression ratios and those engines could crank and fire in almost any temperatures without glow plugs!
*some problems
But yeah it could definitely take longer for the start up pings to go away. On these small diesels the EGR is basically the only way we can retain heat. The natural dissipation into the block is just way too slow.
 

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Anyone have tips for removal, inspection, and cleaning of the EGR valve? It's topside on the engine, right? A fairly easy job to do?
yes. it is topside and easy to change the egr valve. I looked at the instructions on alldatadiy.com a while back - factory service manual info is on-line. The egr cooler on the other hand - that looked like a bit more work.

send me a private message with your e-mail and I can print out the instructions and send them to you.

If you have trouble finding an egr valve - I have a new one in the garage.

jeff
 

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Lol.

I used to send my girlfriend a snap of mine set to Simon and Garfunkel's The Sounds of Silence ("Hello darkness my old friend ... I've come to talk with you again ...") every time mine turned on.

I think my longest streak without it illuminating was about 12,000 miles/14 months through quarantine.
 

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Discussion Starter · #16 ·
The egr cooler on the other hand - that looked like a bit more work.
The EGR cooler was replaced under warranty. I don't recall the exact mileage, but it was maybe 25,000 miles or around there. It was some CEL codes that the GM technical HQ said replace it, and it was a new part number that presumably has some changes made to it. A few other people here had that done.
 

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Discussion Starter · #17 ·
On these small diesels the EGR is basically the only way we can retain heat.
I think it's a fine balancing act and the engine flip-flops between EGR cooling depending on needs.

During a cold start, you want some of that hot EGR going into the intake so that combustion can be stable, reliable, and as complete as possible. You want hot air in the cylinders for the best combustion possible and you also want hot exhaust temperatures flowing into the catalysts and DPF to warm them up as fast as possible. In freezing temperatures you want hot exhaust gas to drive the moisture out of the DPF so it doesn't freeze or so the moisture doesn't create a goo/slime with soot in the DPF.

Then, when you're trying to warm the engine up in cold weather, you want EGR going through the cooler so that heat is being shed into the coolant. You want the coolant and overall engine temperature to warm up so that the engine can have lower emissions, lower wear, faster warmup, etc., but you also want some heat going into the passenger compartment for climate control.

Then, when everything is running at temperature you want the EGR to be cooled as much as possible so that you can have it cooler when being fed into the intake for lower combustion temperatures for lower emissions. High levels of NOx are formed with high combustion temperatures so you want a lean intake air mixture to lower combustion temperatures, and you have to cool that EGR gas down to lower intake temperatures as much as possible.

Lastly, I'm not 100% certain but I believe the EGR is entirely bypassed when the DPF is going through a regen cycle. You want the hottest exhaust gas possible to heat that DPF up, so the EGR is closed off to make sure the cylinders get the cleanest intake air possible for high combustion temperatures. Those high temperatures are then spiked a little bit more with some extra fuel injected during exhaust strokes to bring the DPF up to temperatures that burn the soot off. NOx probably spikes during regen, but the EPA gives waivers for temporary engine operating conditions that are rare and limited and don't often happen. DPF regen is where it has to be done and NOx output is allowed to be higher to make that happen.
 

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Then, when everything is running at temperature you want the EGR to be cooled as much as possible so that you can have it cooler when being fed into the intake for lower combustion temperatures for lower emissions. High levels of NOx are formed with high combustion temperatures so you want a lean intake air mixture to lower combustion temperatures, and you have to cool that EGR gas down to lower intake temperatures as much as possible.

Lastly, I'm not 100% certain but I believe the EGR is entirely bypassed when the DPF is going through a regen cycle. You want the hottest exhaust gas possible to heat that DPF up, so the EGR is closed off to make sure the cylinders get the cleanest intake air possible for high combustion temperatures. Those high temperatures are then spiked a little bit more with some extra fuel injected during exhaust strokes to bring the DPF up to temperatures that burn the soot off. NOx probably spikes during regen, but the EPA gives waivers for temporary engine operating conditions that are rare and limited and don't often happen. DPF regen is where it has to be done and NOx output is allowed to be higher to make that happen.
The idea of egr emissions wise is having some inert gas (inertish) for combustion heat to mix into.
Otherwise we get micro pockets where NOx formation is spontaneous. Cooling the gas just makes it more effective as a heat sink. As long as the EGR is lower than like 1000F it’s effective.

While diesels run cooler than gasolines this isn’t really true on a microscopic scale. Diesels are significantly hotter than gasolines in the cyllinder simply due to the pressures involved.

Anyway yes EGR shuts off for most of a Regen. I don’t exactly know why, but I’m guessing it’s to prevent choking on your own fuel. It could also lead to lots of combustion in the intake which probably isn’t a great idea.
 

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Discussion Starter · #20 ·
Anyway yes EGR shuts off for most of a Regen. I don’t exactly know why
To regenerate the DPF you have to heat it up really hot. You want in-cylinder combustion temperatures to be as high as possible, and to do that you need 100% clean intake air so the EGR doesn't quench the temperatures with inert gases. Then, you are also injecting excess fuel to heat it up even more, and you need as much O2 as possible for that extra combustion. Lastly, you want the soot in the filter heated up as much as possible to combust and flow out the exhaust as CO2, and for that you need extra O2 so the carbon (soot) can combine with that and flow through.

EGR would do nothing but hurt performance of regeneration of the DPF. It's got to be bypassed to make it work.
 
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