Category: Technical Articles

Delphi Smart Injectors and Electronic Unit Pumps

• On : October 9, 2020
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How Delphi Smart Diesel Fuel Injection Technology Works

The Delphi smart injector for medium to heavy duty diesel engines is a high pressure, electronically-controlled diesel fuel injector that is designed to be combined with the Delphi electronic unit pump (EUP). This combination provides a complete high pressure fuel delivery system for “cam in block” engines or engines with separate cam boxes.

Currently, only Delphi combines an electronic unit pump with an electronically-controlled smart injector for DAF engine applications. The injector’s nozzle control valve is electronically-controlled, which helps to reduce fuel consumption and improve performance, all while meeting the most stringent emissions regulations.

When paired with a smart injector, the precise start of injection can be further adjusted by the injector control circuit. Delphi’s EUP’s use proven valve technology from Delphi’s EUI product line. When used in conjunction with the high pressure electronically-controlled smart injector, the EUP provides a complete high-pressure fuel delivery system for heavy duty engines.

The EUP (electronic unit pump) operates in the following manner:

• Filling plunger descending, valve open
• Pre-spill plunger rising, valve open
• Pumping plunger rising, valve closed
• Spill plunger rising, valve open – refer to diagram below

The pumping mechanism is identical to an inline or single cylinder pump. The plunger – which is driven by the camshaft – moves up and down in the body. Pressurised fuel moves freely from the engine fuel manifold, through the pump, and back into the manifold.

At a certain point during the pressure stroke, current is supplied to the actuator. This current generates a magnetic field within the actuator and causes the high-pressure valve to close.

Once this valve is closed, fuel cannot exit the unit back into the engine fuel manifold. The action of the plunger upon the fuel creates very high pressure.

Due to the precise operation of both the EUP and smart injectors, specialised Delphi tooling and test equipment is required to be able to repair, test and calibrate EUP and smart injectors.

Cornells, an authorised Delphi repairer, has all the tooling and equipment required to offer customers testing, overhaul and new replacement EUP and smart injectors. For more information please contact us on +61 3 9267 8800

The Basics of EGRs

• On : October 2, 2020
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EGRs – what they do, how they work, how to troubleshoot

Part of a vehicle’s engine management system, the exhaust gas recirculation (EGR) valve recirculates finely metered quantities of exhaust gas to the engine intake system for increased engine efficiency, and reduced fuel consumption and NOx emissions.

With growing pressure to reduce emissions, the EGR valve will play an increasingly important role moving forward. It’s important to know what it does, why it fails and how to replace it when it does fail.

The EGR valve effectively changes the air entering the engine. With less oxygen, the air mixture burns slower, lowers temperature in the combustion chamber by almost 150°C, and reduces NOx production for a cleaner, more efficient exhaust.

The EGR valve has two primary settings: open and closed, although the position can vary between the EGR valve being closed and when the engine is starting up. During idle and at low speeds, only a small amount of power is required, and therefore only a small amount of oxygen, so the valve gradually opens – it can be up to 90% open at idle.

However, as more torque and power are required (eg. during full acceleration), the EGR valve closes to ensure as much oxygen enters the cylinder as possible. EGR valves can be used to improve combustion efficiency and knock tolerance. In diesels, it can also help to reduce diesel knock at idle.

Types of EGR valve

Although there are several types of EGR valves, earlier systems use a vacuum-operated valve, while newer vehicles are electronically-controlled. The main types of EGR’s are summarised below:

• Diesel high pressure EGR valves divert the high-flow, high-soot exhaust gas before it enters the diesel particulate filter – the soot combines with oil vapor to create sludge. The gas is then passed back to the inlet manifold, either via a pipe or internal drillings in the cylinder head. A secondary valve is also used to help create a vacuum in the inlet manifold, as this is not naturally present on diesel engines.
• Diesel Low pressure EGR valves divert the exhaust gas after it has passed through the diesel particulate filter. This gas has a lower flow, but is almost completely clean of soot. The gas is then passed back to the inlet manifold via a pipe.
• Gasoline EGR valves divert the exhaust gases, much like the high-pressure diesel equivalent. The vacuum created by cylinder depression, draws the exhaust gases in. The flow is regulated by the opening and closing of the EGR valve.
• Vacuum operated EGR valves use a vacuum solenoid to vary the vacuum to the diaphragm, and open and close the EGR. Some valves also include a feedback sensor to inform the ECU of the valves position.
• Digital EGR valves feature a solenoid or stepper motor and, in most cases, a feedback sensor. These valves receive a pulse width modulated signal from the ECU to regulate exhaust gas flow.

Why do EGR valves fail?

EGR valves operate in a complex environment and are prone to wear and tear. However, the single biggest cause of failure is the buildup of carbon particles from the exhaust gases along the EGR and intake system passages. Over time, this will clog tubes, exhaust gas channels and eventually the valve’s plunger mechanism, causing it to either stick in the open or closed position. Failures can also be caused by a rupture or leak in the valve diaphragm.

The symptoms associated with EGR valve failure are similar to those of many other engine management components, and because of this, EGR faults continue to be a source of headaches for many technicians. However, there are a few signs to look out for, such as:

• Check engine light: as with most engine management components, a problem with the EGR valve may trigger the check engine light.
• Engine performance issues: if the valve is stuck open, the vehicle’s air-fuel ratio will be disrupted causing engine performance issues such as reduced power, poor acceleration and rough idle. It may also produce turbo boost pressure leaks, causing the turbo to work harder.
• Increased NOx emissions: when the EGR valve remains closed, the resultant high temperatures in the combustion chamber will leave a lot of unburned fuel in the exhaust, leading to increased NOx emissions and reduced fuel efficiency.
• Engine knock: the higher temperatures and NOx may also result in increased detonation or knock, heard as knocking noises in the engine.

Troubleshooting an EGR valve

Given the different types of EGR valves, it is always best to follow the troubleshooting procedures detailed in the service manual. However, there are a few common steps that can help to perform diagnostics:

1. Read fault codes using a Diagnostic Scan Tool* capable of reading fault codes in the EGR system.
2. Check that all vacuum lines and electrical connections are connected and positioned correctly.
3. Use a vacuum gauge to check the vacuum supply hose for vacuum at 2000 to 2500 rpm. No vacuum at normal operating temperatures would suggest a loose hose, a blocked or faulty ported vacuum switch or solenoid, or a faulty vacuum amplifier/pump.
4. Check the vacuum solenoid while engine is running. On electronically-controlled EGR valves, activate the solenoid with a scan tool and check the vacuum at end of pipe. If the solenoid does not open when energised, is stuck in the open or closed position, or has a corroded electrical connection, loose wire or bad ground, EGR operation will be affected.
5. If possible, check the movement of the valve stem at 1500 to 2000 rpm. The valve stem should move if the valve is functioning correctly. If not, and there’s vacuum, there’s a fault.
6. Apply vacuum directly to the EGR valve using either a hand vacuum pump or scan tool depending on the type of EGR valve. If there is no change in idle quality, then either the EGR valve is faulty or the passages are completely restricted. If the engine idles rough or stalls, the problem is being caused by a malfunctioning control system.
7. Remove the EGR valve and check for carbon build up. Where possible, remove any carbon, being careful not to contaminate the diaphragm.
8. Inspect the EGR passageway in the manifold for clogging and clean if required.

*The ease of replacing an EGR – as with the advancement in EGR technology – has become more complex and time-consuming. In the past, EGR replacement could be done in hours. Now, EGR replacement can take up to 8 hours on some passenger vehicles. That’s why it’s imperative to have a scan tool that has strong emissions testing and calibrating capabilities to help diagnose EGR related issues.

At Cornell’s we have put a lot of time and effort in understanding and diagnosing EGR systems and their failures. Our qualified technicians have built up a wealth of knowledge that helps them diagnose EGR system failures quicker, and helps to reduce the cost of EGR repairs. For further information please call us on 03 9267 8800

Diesel Particulate Filters

• On : May 4, 2020
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What is a DPF (Diesel Particulate Filter)?

A DPF is used in diesel vehicles that comply with Euro-6 emission standards. The manufacturers use the DPF to filter, store and burn the soot particles that are emitted as a result of the combustion process of the diesel engine. DPF’s come in a common cylindrical unit. The DPF consists of silicon carbide. It can filter about 99% of solid particulate matter from the exhaust of a diesel engine. The soot particles or the carbon particles deposit on the filter channels are oxidised into carbon dioxide at exhaust temperatures above 600degC. Basic DPF’s are the single use type. You need to dispose or replace them when they get full, after accumulating ash and when regeneration is no longer possible.

What are Particulates?

Particulates are a form of carbon that accumulates in the exhaust system of the vehicle’s engine, originating from various leftovers that define what type they are. In term of vehicles, particulates are the minute solid particles of exhaust gases emitted from the engine. The engine emits these particulates mainly in the form of carbon or soot. The particulate matter forms a layer of carbon inside the exhaust system of the engine. This is the main reason why taking care of the exhaust system of the engine is so important. It is necessary to limit the quantity of emitted carbon particulates to prevent environmental pollution.

How does a DPF work?

The unfiltered exhaust flows through the DPF’S channels that open at the inlet end. The core contains porous walls of a ceramic honeycomb structure made of silicon carbide. The exhaust gases then enter into the channels that are open at the outlet end. The exhaust system takes away the exhaust gases. The DPF core retains the soot particles and later burns them off during the regeneration process. The ECU computes the amount of soot and ash accumulation in the DPF with the help of the DPF differential pressure sensor.

Components of a DPF

The temperature sensor upstream of the DPF detects the temperature of the exhaust before it enters the DPF. The integral resistor changes its electrical resistance according to the exhaust temperature and then sends a corresponding voltage signal to the ECU control unit. The control unit uses the voltage signal to monitor the rise in exhaust temperature before and during the regeneration process. The DPF differential pressure sensor detects the difference between the exhaust upstream and downstream of the DPF. The exhaust pressure sampling pipes – upstream and downstream of the DPF – detect the exhaust pressure difference. The pressure difference between the exhaust pressures upstream and downstream of the DPF acts on the piezo electric pressure sensor element. This produces a voltage which is passed into the ECU as a voltage signal.

What is Regeneration?

Regeneration is the process that burns off the soot particles accumulated in the DPF as C02. The regeneration takes place when the ECU detects a certain pressure difference in the DPF, then at a certain speed usually above 80kph the DPF temperatures will raise to about 600 degrees Celsius, causing the soot build up to burn away. This will continue until the pressures in the DPF fall back into specification. That is why it is recommended that a vehicle with a DPF be driven on a freeway at least 20 minutes every week to initiate a regeneration (please consult vehicle owner’s handbook).