[steve 135+]

What you have to remember is, how often do you service your car??? this as a lot to do with smoke when tuning boxes are fitted.

The best policy is to change all filters and engine oil, use a good oil and standard filters as some air filters on the market are oil based and can knacker Maf sensors up.

EGR bypass is a good thing in my book, no **** going back into the air intake, PCV this was classed as none serviceable item but if its not serviced, well loads of problems come from not doing so, fit the filter-less type and forget about it.

Any diesel engine they like to suck as much clean air in as possible and a unrestricted exhaust, also don't forget about general wear of the engine! as this can give smoke.

At the end of the day, it's how your car as been looked after, as said one member with no smoke and others with smoke.

The best thing to do is compare your car engine with number 6 and see if theres any differences in engine modifications and service history?

And as always before your MOT is due, service your car and take it for a good run before testing, Steve