Solving cold start problems in TDI engines with pump-injector technology
Cold-start problems with your TDI: Identify the causes and solve them properly
If your TDI engine is hard to start in the morning, cranks for a long time or only starts after several attempts, there can be various causes. The problem often lies in the fuel supply. In unit injector engines, however, leaking PD injectors or wear at their seats in the cylinder head can also be responsible.
Why is my TDI hard to start after standing for a long time?
With this starting behaviour, it is worth checking whether the fuel lines drain after the engine is switched off or whether sealing around the PD injectors is impaired. The PFS-Kit addresses the lines draining; the PD injector bridge or PD injector retainers provide additional stabilisation for compatible PD injectors. Which approach helps depends on the cause identified.
Not all cold-start problems are the same
For a lasting repair, it is crucial to establish whether the problem comes from the fuel supply or whether the unit injectors are no longer properly seated mechanically in the cylinder head.
Air in the fuel system or diesel draining back
After a long period of standing, sufficient diesel is not immediately available at the unit injectors when starting. The system first has to purge the air again.
Leaking PD injectors or wear at their seats in the cylinder head
Movement of the unit injectors in the cylinder head can place stress on the sealing surfaces. The PD injectors then no longer maintain a reliable seal over the long term.
Air in the fuel system or diesel draining back
Normally, the fuel pump continuously moves diesel fuel from the tank to the cylinder head and back again to ensure that enough fuel is always available for the injectors. After a long period of standing, particularly overnight, however, a crucial problem can arise: the fuel lines in the cylinder head are partly filled with air and are not immediately refilled completely with diesel when starting.
Causes include the small cross-sections of the lines and the fact that trapped air cannot escape immediately. Only the continuous operation of the injectors during the starting attempt purges the air from the system again.
This air-purging process becomes noticeable through longer starting attempts, known as prolonged cranking. In the meantime, unburnt fuel can enter individual cylinders and pass the piston into the engine oil. This can lead to engine oil dilution by diesel fuel, often also referred to as a rising oil level.
Leaking unit injectors in the cylinder head
In TDI engines with unit injectors, poor starting can also be caused by the mechanical seating of the PD injectors.
Cold-start problems in TDI engines with unit injector technology are not always solely related to air in the fuel system or fuel draining back. Another known cause is leaking unit injectors, which can result from the PD injectors wearing into the aluminium cylinder head.
The reason lies in the design of many unit injector engines from the Volkswagen Group: the unit injectors sit directly in the cylinder head and are held only at specific points as standard. High injection pressures, engine vibrations, alternating thermal loads and many hours of operation can allow the PD injectors to move slightly in their seats.
Over time, this can cause the unit injector to wear into the cylinder head. The result: the sealing surfaces are subjected to stress, the sealing rings can no longer maintain a reliable seal over the long term, and fuel can pass the sealing areas.
This problem, too, may initially manifest itself through poor starting: the engine is hard to start when cold, runs roughly after starting, judders or needs several starting attempts. A diesel smell in the engine oil, an increasing oil level, a rising oil level, loss of power or recurring leaks at the unit injectors may also occur.
ORIGINAL 07eins PD injector bridge and PD injector retainers
If the cause lies in the mechanical seating of the unit injectors, the 07eins solutions act directly on the PD injector in the cylinder head.
ORIGINAL 07eins PD injector bridge
The ORIGINAL 07eins PD injector bridge permanently stabilises and centres the unit injectors in the cylinder head. It was specifically developed to reduce movement of the PD injectors and support the sealing rings' sealing function.
ORIGINAL 07eins PD injector retainers
The ORIGINAL 07eins PD injector retainers are the more universal solution for numerous TDI engines with Bosch unit injectors. They stabilise the PD injectors directly at their seats and help improve the mechanical seal over the long term.
The solution for fuel draining back: the 07eins Performance Fuel Supply Kit
If cold-start problems are caused by fuel draining back or air in the fuel system, the Performance Fuel Supply Kit directly addresses this cause.
How the Performance Fuel Supply Kit works
The 07eins Performance Fuel Supply Kit was developed to solve cold-start problems caused by fuel draining back or air in the fuel system.
The Performance Fuel Supply Kit features a special 2-channel threshold-pressure valve that connects to the vehicle's original fuel couplings. This valve automatically isolates the cylinder head from the rest of the fuel system as soon as the engine is switched off.
The valve's pressure thresholds are adjusted so precisely that neither engine operation nor the fuel pump's function is restricted.
As a result, the cylinder head always remains filled with fuel, even when the engine stands for a long time. The injectors can therefore be supplied with diesel immediately and without delay at the next start.
Which 07eins solution is right for my TDI?
For the VW T5 2.5 TDI (all engine codes), the PD injector bridge is a product option for additional PD injector stabilisation. PD injector retainers stabilise the individual PD injector bodies and are available in appropriate sets for 3-, 4-, 5- or 10-cylinder engines, depending on the engine. A dedicated 16V PD injector bridge is available for compatible 2.0 TDI 16V engines with BOSCH PD injectors. The PFS-Kit takes a different approach: it is intended to prevent the fuel lines from draining after the engine is switched off. The vehicle, engine code, PD injector version and specific findings help guide the choice; the PD Injector Problem Check provides initial guidance.
Starting problem mainly after standing
If your TDI is mainly hard to start after standing for a long time but then runs largely normally, the cause may be air in the fuel system or diesel draining back.
Cold-start problems plus a rising oil level or juddering
If a rising oil level, a diesel smell in the engine oil, juddering, loss of power, rough running or leaks at the PD injectors also occur, the PD injector seats in the cylinder head should be checked.
Assess cold-start problems correctly – and solve them precisely
Cold-start problems in TDI engines with unit injector technology can have different causes. If the problem arises from fuel draining back or air in the fuel system, the 07eins Performance Fuel Supply Kit is the appropriate solution.
If, on the other hand, leaking unit injectors, wear at their seats or unit injectors that are no longer seated correctly in the cylinder head are the cause, the ORIGINAL 07eins PD injector bridge and ORIGINAL 07eins PD injector retainers act directly on the mechanical cause.
Accurate diagnosis is therefore crucial: poor cold starting after a long period of standing can indicate fuel supply problems. Poor cold starting combined with a rising oil level, a diesel smell in the engine oil, rough running, juddering, loss of power or recurring leaks at the PD injectors, on the other hand, often points to a mechanical PD injector problem in the cylinder head.
Find the right solution for your TDI
Whether it is fuel draining back, air in the system or a mechanical PD injector problem: 07eins offers the right solution for your TDI with unit injectors, depending on the cause.
