'excuse my ignorance james but what is wps thanks paul'

Not at all mate.

I think Lee explained the WPS excellent

It is one of them tools you have to practice with or you will find it hard to use and time consuming and it will end up in a cupboard gathering dust.... I know, I have done this twice LOL

It is worth practicing though... it is a very good friend when you suspect compression issues

This management systems monitors even slight misfires very closely and is keen to save the CAT hence shutting off the injector.
It is amazing the small differences in cylinder pressure that can cause the above chain of events...

With this engine... even the WPS can't save you sometimes... but a standard compression gauge will point the fault out like a sore thumb.

When approaching one of theses bast$%ds with a misfire LOL

Watch the misfire counts like a hawk, just like the ECU does. You should be able to see what makes the misfire counter tick and find the ideal condition to do your tests... keep an open mind and suspect ign, fuel and compression because these have them all!

If it turns out to be compression then I like to know the cause before the head comes off because the fault is not always obvious and then you have to worry until the car is put back together.

Bang the cylinder leak down tester in the offending cylinder.

What are your compression results hot and cold?

What conditions makes the misfires more frequent... try this with different loads whilst stationary aswell, if you can re-enact the misfire in the garage it makes life easier when doing the testing

hth
James