blackwolf wrote:

The issue of oil dilution with fuel is more commonly down to the DPF regen operation than any kind of injector malfunction, and is the reason that all (or nearly all?) vehicles with DPFs have an Oil Service light.

As I understand it, the regen cycle can be initiated in two ways. The 'best' method, and unfortunately the more expensive method, is to have a separate injector that injects fuel directly into the DPF when regen is needed. The fuel ignites, the soot particles are incinerated and the combustion byproducts shoot out of the exhaust, and everything is good. No enigne damage occurs (I am not sure about environmental damage, but presumably someone has decided that incinerated soot is OK whilst unincinerated soot is bad).

The cheap and hence almost universal method, however, works differently. The principle of dosing the DPF with fuel to burn the soot is the same, but the fuel gets there in a very different way. In this method, the ECM is programmed to inject a second dose of fuel into each cylinder during the exhaust stroke of the engine. Since there is no compression on this stroke, the fuel does not ignite and is carried by the exhaust gas from the cylinder to the DPF (or usually combined DPF/Cat) where is is subsequently ignited. Clearly this onlt takes place for a short period every now and then when the DPF regen is needed, but the potential consequences are pretty readily apparent - unburnt fuel is intentionally injected into a cylinder where it will not ignite, and it is inevitable that not all this fuel will be swept up by the exhaust gas and cleared from the cylinder. The residual fuel is then present in the cylinder for another full stroke before (hopefully) being burned off in the next ingition event, and during this time some will migrate past the rings into the sump. In time, especially on vehicles which do predominantly short journeys and regen more frequently, and vehicles with high mileages with more bore wear, this will lead to the sump filling with fuel.

As an aside, injector spray patterns are very highly developed and optimised to cause the flame front to travel through the cylinder in a particular way, both to maximise the amount of fuel combusted (and reduce emissions) and prevent diesel knock, there's a whole science to this. Injectors however can only spray one pattern, and I have little doubt that the pattern to optimise combustion is not the pattern you'd use to optimise the atomisation of fuel in the flow of exhaust gas out of the cylinder for a DPF regen.

This is one of the reasons - indeed possibly the most significant reason - why I would still buy a 2.4 rather than a 2.2 any day of the week!

Tim in Scotland wrote:

I believe JLR is also carrying out a similar mod/update on Ingenium Diesels and SDv6 that have been suffering the oil dilution problem. Those who know about these things claim that all the update does is that it allows a greater amount of oil dilution by fuel before the service due message is flagged on the dash or the EML comes on...........

blackwolf wrote:

The issue of oil dilution with fuel is more commonly down to the DPF regen operation than any kind of injector malfunction, and is the reason that all (or nearly all?) vehicles with DPFs have an Oil Service light.

As I understand it, the regen cycle can be initiated in two ways. The 'best' method, and unfortunately the more expensive method, is to have a separate injector that injects fuel directly into the DPF when regen is needed. The fuel ignites, the soot particles are incinerated and the combustion byproducts shoot out of the exhaust, and everything is good. No enigne damage occurs (I am not sure about environmental damage, but presumably someone has decided that incinerated soot is OK whilst unincinerated soot is bad).

The cheap and hence almost universal method, however, works differently. The principle of dosing the DPF with fuel to burn the soot is the same, but the fuel gets there in a very different way. In this method, the ECM is programmed to inject a second dose of fuel into each cylinder during the exhaust stroke of the engine. Since there is no compression on this stroke, the fuel does not ignite and is carried by the exhaust gas from the cylinder to the DPF (or usually combined DPF/Cat) where is is subsequently ignited. Clearly this onlt takes place for a short period every now and then when the DPF regen is needed, but the potential consequences are pretty readily apparent - unburnt fuel is intentionally injected into a cylinder where it will not ignite, and it is inevitable that not all this fuel will be swept up by the exhaust gas and cleared from the cylinder. The residual fuel is then present in the cylinder for another full stroke before (hopefully) being burned off in the next ingition event, and during this time some will migrate past the rings into the sump. In time, especially on vehicles which do predominantly short journeys and regen more frequently, and vehicles with high mileages with more bore wear, this will lead to the sump filling with fuel.

As an aside, injector spray patterns are very highly developed and optimised to cause the flame front to travel through the cylinder in a particular way, both to maximise the amount of fuel combusted (and reduce emissions) and prevent diesel knock, there's a whole science to this. Injectors however can only spray one pattern, and I have little doubt that the pattern to optimise combustion is not the pattern you'd use to optimise the atomisation of fuel in the flow of exhaust gas out of the cylinder for a DPF regen.

This is one of the reasons - indeed possibly the most significant reason - why I would still buy a 2.4 rather than a 2.2 any day of the week!