Thread: What happened to your D3/D4 today?

Speculation. Read the FM. Specifically 412-04.

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Idle Speed Control
In order to maintain A/C cooling performance, the ATCM requests an increase in engine idle speed if the evaporator
temperature starts to rise while the refrigerant solenoid valve is already set to the maximum flow rate.

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The ATCM manages the vehicle electrical loads to:

• Maintain the vehicle battery in a healthy state of charge.
• Ensure adequate power is available for defrost demisting during engine warm-up.
• Ensure adequate power is available for A/C during extended periods with the engine at idle speed.
• To maintain system voltage within acceptable limits.
• To provide adequate power to meet customer expectations.

Electrical load management is achieved by increasing the engine idle speed and controlling the electrical load of systems that do not affect the driveability or safety of the vehicle.

What does that have to do with the EGR butterfly?

Originally Posted by Graeme

What does that have to do with the EGR butterfly?

SFA. The EGR butterfly post was posted while I was looking up the elevated idle.

Originally Posted by discorevy

Butterfly valve is only for EGR on the engine in question, it's not petrol type throttle position.

????????? I was not talking about egr at all. The throttle is fly by wire, there are no mechanical linkages between the pedal and the throttle on the D4 v6 diesel.

Originally Posted by Eric SDV6SE

????????? I was not talking about egr at all. The throttle is fly by wire, there are no mechanical linkages between the pedal and the throttle on the D4 v6 diesel.

You implied the butterfly valve moves in relation from input from the go pedal. That is not correct. The accelerator pedal has nothing to do with the position of the butterfly valve. In a diesel, fuel volume is used to govern the engine, not air. The throttle valve remains fully open at all times aside from (supposedly, not my info) when it closes to run off the EGR system.

Copy that, i stand corrected, point still being that from the OP's question, there is no mechanical linkage that would be causing higher idle rpm. It has been clarified by BradC why the higher idle rpm condition occurs.

Originally Posted by Eric SDV6SE

Copy that, i stand corrected, point still being that from the OP's question, there is no mechanical linkage that would be causing higher idle rpm.

Just to clarify the clarification, elaborate on the post from Tombie and try and simplify a complex process, while honestly not trying to teach anyone to suck eggs:

In the old days, you would stab the throttle which would push on a spring in the injection pump that relayed that force via the governor to the fuel rack, causing each stroke of the injection pump to inject more fuel. On clever injection pumps there was also a "smoke limiter" device that restricted the fuel rack extension based on intake manifold boost pressure. Diesels have *never* had a throttle (which is one of the reasons they have better pumping efficiency than a petrol motor). The throttle on the TDV6 is to allow easier EGR flow.

These new fangled 'lectrical units are entirely computer controlled. That makes things like HDC and cruise control dead easy. You stab the pedal, it increases the voltage (and decreases because the throttle pedal sensor is a double-opposed for redundancy) to the computer. The computer says, "I'm doing 1600RPM at cruise and the driver has asked for a ****load more power, my tables say I can inject --> <-- this much fuel to increase power without smoking, so I'll do that".

It is entirely electronic. The computer controls the common rail pump pressure, and opens each injector individually (up to 6 times per event) to control how much fuel is injected, and precisely when each injection event occurs (again, up to 6 per stroke). It's incredibly clever and from the outside looks quite complex, but from a diagnostic point of view it's a group of sensors into the computer, and 6 injectors plus 2 valves (VCV and PCV on the HPFP).

On that basis, it's also pretty easy to diagnose if you understand the process.

Sensors : MAP, MAF, IAT, Pedal, Fuel temperature, rail pressure, coolant temperature & oil temperature.
Actuators : 6 Injectors, VCV & PCV.

That's it. Nothing more complex. The cervix manuell spells the relevant processes out in some detail, so it's all listed in black and white.

My diesel Fiat 411R tractor has a butterfly that is operated at the same time the injector pump is operated. I don't know the reason for it being fitted though but perhaps to prevent engine runaway.