14 hours ago, mkratky said:

Hi Luke,

It’s great to hear that your S-Max is running well again.

It really was an unbelievable cause. There’s a 10-bar non-return valve in the return pipe, and it’s a very important component for the piezo injector system.

Your post pointed me in the right direction to find the problem. Without this topic, both my S-Max and yours would have been out of service for good.

I wish you no more problems with your car.

 

@mkratky could you please elaborate, especially the location (picture?) of the valve ?

Having seen leak off tests where each injector is fed to an open bottle, I thought that the leak off pipes simply drained freely back to the tank and don't understand why a non-return valve would be necessary?

It does seem that "cheap" return pipes may have an issue but I still don't understand the reason for that. However, in case I have that issue, I want to be able to go straight to the root of the problem.

Thanks

On 9/13/2025 at 11:24 AM, Shearers said:

@mkratky could you please elaborate, especially the location (picture?) of the valve ?

Having seen leak off tests where each injector is fed to an open bottle, I thought that the leak off pipes simply drained freely back to the tank and don't understand why a non-return valve would be necessary?

It does seem that "cheap" return pipes may have an issue but I still don't understand the reason for that. However, in case I have that issue, I want to be able to go straight to the root of the problem.

Thanks

Here’s a picture of the non-return valve. It’s located at the end of the return pipes and opens at 10 bar. I tested it with compressed air at 9.5 bar, and it didn’t open.

I think the engine can run fine at idle during a leak-off test without the non-return valve, but at higher loads the injectors can’t open and close precisely and quickly enough without the 10-bar backpressure.

Don’t worry too much about this issue – I believe it usually appears only after replacing the return pipe. Unfortunately, I’m now running a new non-original return pipe. The car pulls with full power, but regenerations happen every 100 km. Could this be another issue, or could it be caused by less precise injector operation due to the return pipe? Could it affect injector correction values?

Luke, how often do you get regenerations with the new return pipe?