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 Post subject: Lean conditions from egr removal??
PostPosted: Sat Dec 07, 2019 1:31 pm 
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I had been reading on VGT and egr working togeather and had a question as far as fueling during egr operation.
The way I’m visualizing this process is that:

1, the egr opens the fcv butterfly either isolates the intake from the charge air system or tapers its flow.

2, The computer somehow accounts for this change orienting the vanes to reduce turbine input and boost press/flow

3, The fueling is changed at this point to accomidate for the a less dense air charge and the combustion somehow resumes in one way or another.

Question:With the egr path removed as well as the fcv deleted durring these events when the computer believes that it is operating the egr pathway, is there a possibility that the air charge in the cylinders is high and leaning out the mixture causing cylinder temps to elevate above design parameters?


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 Post subject: Re: Lean conditions from egr removal??
PostPosted: Sat Dec 07, 2019 1:36 pm 
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This is a fundamental misunderstanding of diesel combustion. Diesels are a lean-burn engine. You WANT there to be an excess of oxygen in the cylinder, so that all the fuel is consumed during the combustion cycle. This keeps temperatures LOW.

When diesels are run rich, that is when cylinder temps rise. It is the exact opposite of a gas engine.

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 Post subject: Re: Lean conditions from egr removal??
PostPosted: Sat Dec 07, 2019 3:08 pm 
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Vmcrdrod wrote:
I had been reading on VGT and egr working togeather and had a question as far as fueling during egr operation.
The way I’m visualizing this process is that:
1, the egr opens the fcv butterfly either isolates the intake from the charge air system or tapers its flow.
2, The computer somehow accounts for this change orienting the vanes to reduce turbine input and boost press/flow
3, The fueling is changed at this point to accomidate for the a less dense air charge and the combustion somehow resumes in one way or another.
Question:With the egr path removed as well as the fcv deleted durring these events when the computer believes that it is operating the egr pathway, is there a possibility that the air charge in the cylinders is high and leaning out the mixture causing cylinder temps to elevate above design parameters?

When you reintroduce exhaust gases back into the diesel engine intake, you are displacing incoming air that is rich in oxygen with exhaust gasses that has little or no oxygen. As a result, the engine doesn’t burn all the injected fuel because there is less available oxygen to support combustion. If anything, the ECM would lower fuel injection rates when the EGR valve is open due to knowing there is not enough oxygen to support complete fuel combustion. But I think most of us are of the opinion that the ECM was not programmed to do this.

Feeding soot laden exhaust gases into the intake of a diesel engine makes engine combustion less efficient, compromising economy and power. The normally "dry" intake system of a diesel engine is now subject to fouling from soot and oil vapors, which can effect or limit total airflow into the combustion chamber. When EGR soot is combined with the oil vapors from a positive crankcase ventilation (PCV) system, it will cause buildup of sticky gooey tar in the intake manifold and on the valves. It can also can cause wear problems with other engine components i.e. rocker arm rollers, bearings, etc. Diesel EGR's also greatly increases soot production leaving the engine's combustion chambers due to incomplete combustion caused by the lack of sufficient oxygen for complete combustion. EGR systems also add abrasive soot contaminants and will increase engine oil acidity, which in turn will reduce engine longevity.

The effects of EGR operation in a diesel engine reduce fuel economy and engine output power an estimated 3% to 5% which means an additional 3%-5% more diesel is consumed and burned to generate the same amount of power.

Is the EGR valve needed? NO, but HECK NO! The EPA does not give a rats behind about engine efficiency or engine longevity. It was all about lowering NOX and they could have cared less about the effects on economy, power, and engine life. And in reality, since it (EGR) causes an increase of 3 to 5% increase of fuel consumption which in turn increases emissions, do they even really care about the environment, really makes you wonder. Was it really simply all about power and control? :furious:

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 Post subject: Re: Lean conditions from egr removal??
PostPosted: Mon Dec 09, 2019 9:51 am 
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 Post subject: Re: Lean conditions from egr removal??
PostPosted: Mon Dec 09, 2019 7:22 pm 
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The tune is looking for a certain manifold pressure from the turbo. It's going to achieve that pressure whether or not the FCV is throttling the engine.

The FCV is actually likely causing increased EGT's because its doing two things:

1. The FCV/EGR combo needs the pressure in the intake manifold to be lower than the pressure in the exhaust manifold to work. Simultaneously the ECU is expecting a certain level of boost at the MAP sensor. Since the turbo now needs to overcome the flow restriction that is the FCV, additional boost needs to be generated at the turbo outlet which means the VNT is going to close up to spin the turbo faster.

The FCV is effectively creating excessive backpressure in the exhaust manifold in order to make the whole system work. Ideally, the intake and exhaust manifold is as close to a 1:1 pressure ratio(or less) as possible for maximum power and efficiency.

2. As others said, you are getting a richer fuel mixture which will lead to hotter EGT's.

Last but not least, a proper tune will tell the ECU not to expect a reduction in the MAF related to FCV usage. If the tuner does more than just shut of the engine codes, the ECU should'nt even be attempting to change any combustion parameters other than running like normal.

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