Popular Mechanics report on CRD Sport

talstar · **Joined:** Thu Apr 27, 2006 4:32 pm **Posts:** 28

Popular mechanics 3rd report: had throttle body replaced or whatever you call it on a diesel. Fuel economy: average 20.3mpg, worst 13.5mpg, best 27.3 mpg

oldnavy · **Posted:** Fri Jul 21, 2006 5:40 pm

talstar wrote:

Popular mechanics 3rd report: had throttle body replaced or whatever you call it on a diesel. Fuel economy: average 20.3mpg, worst 13.5mpg, best 27.3 mpg

D/C calls it an EGR Flow Control Valve, most diesel heads call it an anti-shudder valve or anti-dieseling valve, I think VW calls it a anti sudder valve.

naturist · **Posted:** Sat Jul 22, 2006 8:07 am

Yeah, the mechanic-who-knew-little about my CRD called it a throttle body too. It LOOKS like a throttle in the gasser sense, and it's located where a throttle body would be on a gasser. But diesels have no use for a throttle, running with maximum air at all times. This thing serves the twin purpose of helping control the mixture of fresh air and recirculated exhaust gases as well as choking off the air on shut-down to make sure the engine actually stops running smoothly.

oldnavy · **Posted:** Sat Jul 22, 2006 10:28 am

naturist wrote:

Yeah, the mechanic-who-knew-little about my CRD called it a throttle body too. It LOOKS like a throttle in the gasser sense, and it's located where a throttle body would be on a gasser. But diesels have no use for a throttle, running with maximum air at all times. This thing serves the twin purpose of helping control the mixture of fresh air and recirculated exhaust gases as well as choking off the air on shut-down to make sure the engine actually stops running smoothly.

You have just contradicted yourself dude.

The Flow Control Valve has nothing to do with control of fresh air as that is what a throttle body does, and it has nothing to do with recirc of exhuast gases because that is what the EGR does.

There are only two reasons for the Flow Control Valve:

1. smooth shut doiwn of engine
2. to prevent run away engine.

That is the only two uses for the valve.

Goglio704 · **Posted:** Sat Jul 22, 2006 10:34 am

oldnavy wrote:

naturist wrote:

Yeah, the mechanic-who-knew-little about my CRD called it a throttle body too. It LOOKS like a throttle in the gasser sense, and it's located where a throttle body would be on a gasser. But diesels have no use for a throttle, running with maximum air at all times. This thing serves the twin purpose of helping control the mixture of fresh air and recirculated exhaust gases as well as choking off the air on shut-down to make sure the engine actually stops running smoothly.

You have just contradicted yourself dude.

The Flow Control Valve has nothing to do with control of fresh air as that is what a throttle body does, and it has nothing to do with recirc of exhuast gases because that is what the EGR does.

There are only two reasons for the Flow Control Valve:

1. smooth shut doiwn of engine
2. to prevent run away engine.

That is the only two uses for the valve.

The service manual also says the valve is used to "increase the EGR flow rate at low engine loads." My diesel Maximas have a similar arrangement. By closing the butterfly it makes the intake pressure negative and increases flow through the EGR.

Click for larger.

oldnavy · **Posted:** Sat Jul 22, 2006 11:34 am

Goglio704 wrote:

The service manual also says the valve is used to "increase the EGR flow rate at low engine loads." My diesel Maximas have a similar arrangement. By closing the butterfly it makes the intake pressure negative and increases flow through the EGR.

Click for larger.

Well it seems someone thinks a diesel with a EGR valve need a throttle body. Never seen one work that way as described in your service manual, diesels do not have vacuum in manifolds. If at idle you start to close that valve nothing really happens except the engine idles down even slower and eventually stops if it is closed too far. What "flow" is increased by closing the valve? Surely not EGR gasses, how would you increase the exhuast gas recirc by closing off/restricting the intake of air that is required to run engine?

Goglio704 · **Posted:** Sat Jul 22, 2006 11:48 am

The way I understood it is this. As you said, a diesel normally never developes vacuum because the intake is wide open. By restricting the intake with the valve, a vacuum is developed. The EGR feeds to the intake after the butterfly, so it is exposed to this vacuum and will flow more than if the valve were open. To put it another way, if you restrict the supply of fresh air, the engine has to find air somewhere. If the EGR valve is open and the intake is restricted the engine will have to pull more through the EGR. I do not claim to fully understand the system, but the service manual indicates an interaction with the EGR.

oldnavy · **Posted:** Sat Jul 22, 2006 11:55 am

From our FSM:

The ECM operates and monitors the EGR valve
and air flow control valve. The ECM is located in the
left-rear side of the engine compartment (Fig. 1).
The ECM will monitor and determine the positioning
of the EGR valve and air control valve by internal
programming defined during engine development.
This will depend on inputs from the engine coolant
temperature, engine load, fuel quantity, throttle position
and engine speed sensors. The air control valve
blends the incoming charge air and the cooled and
recirculated EGR gasses, to be used again in the
combustion chamber.

The above is a basic discription of a TB operation

Exhaust gas recirculation will begin in this order
when:
² The ECM determines that EGR system operation
is necessary.
² The inlet seat (poppet valve) at the bottom of
the EGR valve opens to dilute and recirculate
exhaust gas back into the intake manifold.
² The EGR Cooler further cools the hot exhaust
gasses before recirculation
The EGR system will be shut down by the ECM
after 60 seconds of continuous engine idling to
improve idle quality and the air flow control valve
will close completely when the vehicle is shut off to
assist with engine shake on shut down.

Strange indeed, throttle body on a diesel. What next???

oldnavy · **Posted:** Sat Jul 22, 2006 11:58 am

Goglio704 wrote:

The way I understood it is this. As you said, a diesel normally never developes vacuum because the intake is wide open. By restricting the intake with the valve, a vacuum is developed. The EGR feeds to the intake after the butterfly, so it is exposed to this vacuum and will flow more than if the valve were open. To put it another way, if you restrict the supply of fresh air, the engine has to find air somewhere. If the EGR valve is open and the intake is restricted the engine will have to pull more through the EGR. I do not claim to fully understand the system, but the service manual indicates an interaction with the EGR.

I understand the the process, I just don't see it working as they think it does. Kind of reminds me of the CCV and how they say that works. Yeah right.

Goglio704 · **Posted:** Sat Jul 22, 2006 12:01 pm

Yeah, I think we are losing some of the inherent symlicity of a diesel by adding these emissions controls. I see a parallel with the early days of gas emissions controls. A lot of wacky stuff being tried, when what was really needed was better fuel management in the form of electronic fuel injection. I know, we already have electronic fuel injection. My point is that we will see some of this overly complex crap until a breakthrough in diesel technology makes the stuff obsolete.

oldnavy · **Posted:** Sat Jul 22, 2006 12:09 pm

Goglio704 wrote:

Yeah, I think we are losing some of the inherent symlicity of a diesel by adding these emissions controls. I see a parallel with the early days of gas emissions controls. A lot of wacky stuff being tried, when what was really needed was better fuel management in the form of electronic fuel injection. I know, we already have electronic fuel injection. My point is that we will see some of this overly complex crap until a breakthrough in diesel technology makes the stuff obsolete.

True, I remember all the vacuum lines and the air pump and other crap that has been reduced or gone now. The big think in the gassers was the switch to unleaded fuel and then as you say, EFI and computer engine management. The diesel seems to have have come all the way finally with the advent of ULSD fuel.

richardkf · **Joined:** Wed Jun 14, 2006 4:15 pm **Posts:** 167

oldnavy wrote:

Goglio704 wrote:

Yeah, I think we are losing some of the inherent symlicity of a diesel by adding these emissions controls. I see a parallel with the early days of gas emissions controls. A lot of wacky stuff being tried, when what was really needed was better fuel management in the form of electronic fuel injection. I know, we already have electronic fuel injection. My point is that we will see some of this overly complex crap until a breakthrough in diesel technology makes the stuff obsolete.

True, I remember all the vacuum lines and the air pump and other crap that has been reduced or gone now. The big think in the gassers was the switch to unleaded fuel and then as you say, EFI and computer engine management. The diesel seems to have have come all the way finally with the advent of ULSD fuel.

how come at the fuel pumps the sticker for ULSD says "do not use in 2007 or later diesel vehicles - can cause damage to engine and other components"? Does this mean that in 2007 another grade of diesel will be available in the pumps? I don't understand.

RFCRD · **Posted:** Sat Jul 22, 2006 1:49 pm

richardkf wrote:

how come at the fuel pumps the sticker for ULSD says "do not use in 2007 or later diesel vehicles - can cause damage to engine and other components"? Does this mean that in 2007 another grade of diesel will be available in the pumps? I don't understand.

The sticker is in place because that's not ULSD, yet. It supposed to be on all retail pumps until the sulfur content is low enough to certify them as ULSD (under 15ppm). What is in the pumps now still has too high of a sulfur content for 2007 emissions, yes it will damage the new hardware.

oldnavy · **Posted:** Sat Jul 22, 2006 2:31 pm

RFCRD wrote:

richardkf wrote:

how come at the fuel pumps the sticker for ULSD says "do not use in 2007 or later diesel vehicles - can cause damage to engine and other components"? Does this mean that in 2007 another grade of diesel will be available in the pumps? I don't understand.

The sticker is in place because that's not ULSD, yet. It supposed to be on all retail pumps until the sulfur content is low enough to certify them as ULSD (under 15ppm). What is in the pumps now still has too high of a sulfur content for 2007 emissions, yes it will damage the new hardware.

All true except the only thing it will harm on a '07 is the particulate traps, not the injection pump, injectors or anything else that I can think of off hand.

Tom_with_a_Dream · **Posted:** Sat Jul 22, 2006 9:43 pm

Quote:

To put it another way, if you restrict the supply of fresh air, the engine has to find air somewhere. If the EGR valve is open and the intake is restricted the engine will have to pull more through the EGR.

This may be along the lines of the now-infamous "travel trailer" but Goglio's interpretation of his Service Manual, which seems spot on to this non-diesel mechanic but otherwise technical person, is that DC has succeeded in creating the first near-perpetual machine...

The exhaust is used to feed the inlet and on and on. All is right with the planet, it seems.

Oh, and Goglio, you got me with the screen capture of the pdf Service Manual. I must have clicked the Adobe toolbar Save button four times befroe realizing it was part of the image and not a toolbar.

Goglio704 · **Posted:** Sat Jul 22, 2006 10:02 pm

If you want to have fun with somebody, leave a full screen image of a screen capture on their computer. :wink:

Popular Mechanics report on CRD Sport

Who is online