This post is designed to give a basic overview of modern Toyota Diesel engines and their commonly troublesome components:
How does a Diesel engine work?
Firstly Diesel is not as flammable as Petrol. Diesel engines don’t have spark plugs to ignite the fuel, but to bring about combustion they require heat. If you put your finger over the end of a foot pump and pump it, your finger will become hot. This is due to compression of the air trapped inside the pump (the air molecules have less space to move about and collide with each other more frequently causing energy to be given off in the form of heat).
The same thing happens in a diesel engine: as the piston moves upwards, the air trapped inside is compressed, causing it to heat up (the temperature reached is circa 400 degrees C). Just before the piston reaches the top of its' stroke, the pump and injectors spray a very fine mist of diesel into the piston chamber. The intense heat of the trapped air in the piston causes the diesel to ignite, forcing the piston down and producing the power stroke which goes through the engine via the gearbox / wheels etc etc and off you go.
What are Glow Plugs?
When internal sensors detect that the core of the engine block has reached a certain designated temperature, or when a certain amount of time elapses, the glowplug relay switches off the "wait-to-start" light. A pre-heating cycle usually lasts for 2 to 5 seconds. The driver then turns the key to the "start" position. The glowplug relay switches off the glowplugs after the engine is running. In some newer cars, glow plugs continue to operate for up to 180 seconds after engine start to keep the engine within emissions regulations, as combustion efficiency is greatly reduced when the engine is very cold. Link http://en.wikipedia.org/wiki/Glowplug
As glow plugs wear out the vehicle will be more difficult to start, run poorly and produce a white/bluey smoke. Glow Plugs are a reasonably cheap to replace.
What is D4D?
D4D is Toyota’s version of Common Rail Diesel. The term "common rail" refers to the fact that all of the fuel injectors are supplied by a common fuel rail which is nothing more than a pressure accumulator where the fuel is stored at high pressure. This accumulator supplies multiple fuel injectors with high pressure fuel. Modern common rail systems, are governed by an engine control unit (ECU) which opens each injector electronically rather than mechanically.
What are Injectors?
Fuel injectors are a key part of modern automotive systems, as they're responsible for getting fuel into the engine in a precise, orderly and carefully engineered pattern. Unfortunately, the conditions we drive in are not ideal. Pollution is in the air, and fuel can be contaminated with water, dirt particles and other debris. Regularly changing your fuel filter (according to change interval in your service book) will help keep debris from circulating. You can also add fuel injector cleaner to your fuel tank, which may help solve running issues. Doing this at regular intervals of 10,000 miles or so might provide more cleansing than your engine actually needs, but it shouldn’t harm the system. Injector Cleaner can't improve your car beyond its original factory spec.
When injectors fail there are generally two approaches to repair, take the vehicle to a main dealer and have the whole set (£1000+) replaced or find a diesel specialist who may be able to replace or repair individual injectors (circa £250 each) after testing. Fuel Injector problem symptoms include, poor starting, rough running, loss of power, black or white smoke. It is generally known that injectors will need attention after 100,000 miles.
What is a Turbo?
Turbochargers are a type of forced induction system. They compress the air flowing into the engine. The advantage of compressing the air is that it lets the engine squeeze more air into a cylinder, and more air means that more fuel can be added. Therefore, you get more power from each explosion in each cylinder. A turbocharged engine produces more power overall than the same engine without the turbocharging.
When Turbo’s are failing they will typically cause the car to have a loss of power, excessive smoke and in some cases a high pitched whine. Turbo’s can often be repaired bya turbo specialists or replaced with a new unit, obviously a repair is cheaper.
What is an SCV?
SCV's (Suction Control Valves) are used in Common Rail diesel engines to control the pressure of the fuel in the accumulator. The pressure is varied by the ECU by controlling how much fuel the pump feeds into the accumulator, replacing the fuel as it is delivered into the engine by the injectors. Low pressure for the injectors at idle, high pressure at maximum power.
Electrically operated, SCVs can need to open and close at up to 200 times per second and if they stick or fail to open properly then poor running, starting and power loss can occur. Sticking when hot is often cited as a cause of hot starting problems. D4D pumps may have one or two of these valves depending on the type of pump fitted, this is important when ordering the correct parts.
Vehicles commonly affected by this have the 1CD-FTV 2.0 D4D Engine 2000-2005, found on RAV4/Avensis/Corolla built between these dates. This article SCV's on the RAV4 Forum provides an overview of the location and parts on a two valve pump. These parts are typically £250 to replace + fitting if required.
What is an EGR Valve?
Exhaust gas recirculation (EGR) is a nitrogen oxide (NOx) emissions reduction technique used in modern engines, EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders. After a while the gases containing dirty, sooty carbons start to cover and coat the intake area and valves causing the air to fuel ratio to become unbalanced thus resulting in more black smoke being emitted from the exhaust. This black smoke is then drawn back into the air intake via the EGR valve. A vicious cycle then starts with the engine producing more smoke and sootier carbons being drawn into the intake, a major problem.
Symptoms of EGR issues include lack of power, engine hesitancy and then a surge of power followed by black sooty smoke. A fall in fuel economy may also occur. On most Toyota engines the valve is easily removed and cleaned, a dealer will charge an hours labour to do the same job. If the valve fails it will cost around £300 to be supplied and fitted by Mr T. If the vehicle is used continually then carbon clogging could eventually lead to head gasket failure on AD engines, please review the attached document to see if your car has one of these engines.AD Head Gaskets.pdf
A simple method of trying to keep the EGR valve clean is to drive the vehicle (once warm) hard by bringing the revs near to the red line, this will result in black soot leaving the exhaust, continue this until the soot no longer appears. This should be a weekly event. This is also known as an Italian Tune Up.
Personally as my 2.2 D4D Verso is out of warranty i clean the EGR every 10k, this a superb guide http://www.toyotaown...howtopic=106241
What is D-Cat?
D-CAT (Diesel Clean Advanced Technology) is Toyota’s version of a diesel particulate filter (DPF) which is a device designed to remove soot from the exhaust gas of a diesel engine. The soot created by the engine is burnt off during the regeneration process, this process uses fuel which is added by an additional injector, this additional fuel usage reduces MPG when compared with vehicles that dont have a DPF. The regeneration process occurs at road speeds higher than can generally be attained during urban usage ,vehicles driven exclusively at low speeds in urban traffic will require periodic trips at higher speeds to clean out the DPF.
On cars with a very high sixth gear the engine revs may be too low to generate sufficient exhaust temperature for regeneration. Occasional harder driving in lower gears should be sufficient to burn off the soot in such cases. With this type of DPF regeneration will be initiated by the ECU every 300 miles or so depending on vehicle use and will take 10 to 15 minutes at 40MPH+ to complete. You shouldn't notice anything other than perhaps a puff of white smoke from the exhaust when the process is completed.
If the DPF doesn’t regenerate properly eventually a warning light will be displayed and the vehicle should be taken to a main dealer. Continued usage past this point may destroy the DPF completely so it must be replaced, this will be very expensive (£1000+).
DPF Continued
If your car is type approved and registered after the date below it will have a DPF to meet the EU Emissions, things can get very complicated here. Vehicles are often built long before being registered, so you could purchase a 2010 car that was a 2009 model. Its important to ask what model year your car is and which emission standard it meets. Its possible to be driving a 10/60 or even an 11 Reg thats not Euro 5 (V) if the car was built long before being registered.
Euro 5 (V) Emissions Standard Commenced - September 2009
If you only drive low mileages in town do not buy a Diesel with a DPF. A Petrol is more suitable.
Modern Diesels are very complex machines, following manufacturer servicing guidelines is essential as is using the correct oils, fluids and drivers checking levels frequently.
The issues mentioned above are not restricted to Toyota's, all manufacturers have these issues and probably more of them.
Hopefully this is useful to people 
Please PM me if any of this requires amending.
