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I know/have heard that the throttle works differently on diesels, and that they don't even need them--technically. How does the 2.8 work?

The reason I ask is yesterday I was going down a rather steep hill coasting at speed with my Torque app open, and when I first checked there was almost no vacuum (or boost). Then I accelerated around at car in the right lane then resumed coasting and the vacuum was at about 23 foot pounds (or inches or whatever).

Does the throttle just open fully under certain conditions even with your foot off the pedal?
 

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The throttle body/plate is purely to help control EGR flow, nothing else. When the EGR valve starts to open the computer will also change the position of the throttle blade so the engine pulls more EGR.

If EGR were disabled then there would be no need to have the throttle body installed. There's actually a throttle body delete kit for the 6.7 Cummins to completely remove it if running a delete tune.

Diesel engines themselves are 100% controlled by fuel and fuel injection timing, there is no need for a throttle plate like with gasoline engines.
 

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The throttle body/plate is purely to help control EGR flow, nothing else. When the EGR valve starts to open the computer will also change the position of the throttle blade so the engine pulls more EGR.

If EGR were disabled then there would be no need to have the throttle body installed. There's actually a throttle body delete kit for the 6.7 Cummins to completely remove it if running a delete tune.

Diesel engines themselves are 100% controlled by fuel and fuel injection timing, there is no need for a throttle plate like with gasoline engines.


@DieselDrax,

So Drax ( I'm fishing for info) does that mean that when engine braking is engaged, the turbo veins are closed, that the ECM would command the butterfly to some other position other then closed to supply more back pressure for better braking efficiency or does the butterfly position not have an effect ?



Thanks Kevin
 

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@DieselDrax,

So Drax ( I'm fishing for info) does that mean that when engine braking is engaged, the turbo veins are closed, that the ECM would command the butterfly to some other position other then closed to supply more back pressure for better braking efficiency or does the butterfly position not have an effect ?



Thanks Kevin
Closing the throttle would reduce the effectiveness of the exhaust brake as it would reduce the volume of air being pumped through the engine. The exhaust brake works by restricting exhaust flow out of the engine, higher RPMs = higher airflow = more exhaust braking ability. Blocking off the ability of the engine to pull air into the cylinders and push it out the exhaust would result in reduced back pressure at the exhaust inlet of the turbo and reduce how effective the exhaust brake is.
 

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Discussion Starter · #5 ·
The throttle body/plate is purely to help control EGR flow, nothing else. When the EGR valve starts to open the computer will also change the position of the throttle blade so the engine pulls more EGR.
Thank you for that. Is there a Torque app setting/widget that lets you know the position? I'm just wondering when it is open and when it is closed, given that in the situation I described it seemingly was open and then closed under very similar conditions.
 

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Thank you for that. Is there a Torque app setting/widget that lets you know the position? I'm just wondering when it is open and when it is closed, given that in the situation I described it seemingly was open and then closed under very similar conditions.
I couldn't tell you, I don't run Android and my in-vehicle monitoring is done with a ScanGauge II. Sorry!
 
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I have a 2016 2.8 Colorado, deleted. It keeps over boosting and blowing the side out of the inner cooler, can not seem to find out what is causing it any answers out there?
Still stock turbo? I would suspect the map sensor if you have no DTCs. Stock turbo vaine actuator has feedback of what position its in.
 

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wait, our 2.8 also has an intake air heater? I thought they just had glow plugs. hmm... the things you learn! But that is interesting to learn what it uses the intake air/throttle valve for. i'd never heard it was used during regen, only that supposedly it was used in conjunction with the egr or that it is closed on shut down to help the motor stop faster supposedly...
 

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There are glow plugs and no intake heater that I've ever seen. Usually it's one or the other, like the Cummins has an intake grid heater instead of glow plugs, we have glow plugs instead of a grid heater.

The throttle valve is for EGR control, that doc claims it's for temperature control during regens, which may be true, and that control is achieved by controlling EGR flow. It's also used outside of regens to control EGR flow more precisely.

So, that doc has some odd misinformation or incomplete information about how things work, IMO.

Sent from my SM-G986U using Tapatalk
 
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"that doc" was written by GM to overview the controls on the new minimax

🤷‍♂️

I know, I read it. There have been various inconsistencies in the info leading up to the launch of the LWN. Not only is there no (obvious) intake heater, there's no fuse or relay for such a thing, only the glow plug module. If there were an intake heater then it would be obvious as there would be some larger-gauge wires running to it similar to what my Cummins had.

It's also unlikely to have such a heater with a composite intake, the intake heaters can put out a lot of heat and there's a risk of damaging/melting the intake. Not a problem with the Cummins because the intake is metal.

All manufacturers make mistakes in various docs, just because a doc says something doesn't mean it's accurate and often times it's easy to verify whether or not something is true.
 

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I know, I read it. There have been various inconsistencies in the info leading up to the launch of the LWN. Not only is there no (obvious) intake heater, there's no fuse or relay for such a thing, only the glow plug module. If there were an intake heater then it would be obvious as there would be some larger-gauge wires running to it similar to what my Cummins had.

It's also unlikely to have such a heater with a composite intake, the intake heaters can put out a lot of heat and there's a risk of damaging/melting the intake. Not a problem with the Cummins because the intake is metal.

All manufacturers make mistakes in various docs, just because a doc says something doesn't mean it's accurate and often times it's easy to verify whether or not something is true.
The service manual says about the valve being used for Regen temperature control too. Use with the EGR wouldn't surprise me either though, turbo vain control helps with controlling EGR also. EGR valve is closed though during regen. The map sensor is a big part of how it monitors EGR flow.

Side note: my s10 factory service manual said not to use a steel drain plug in the aluminum transfer case. What did they do from the factory , use a steel one.
 
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