Have you changed the pressure switch?

oil light comes on when at idle and up to engine temp.had engine flush and new oil pump fitted.engine doesnt sound as smooth as my partners c-max fitted with the same engine.fords done a pressure check and its 1.8 at 2000 rpm.any help could it be crankshaft bearings.looking to trade car if it is.

[1] by "Ford" I presume you mean your dealer?

[2] 1.8 bar (26psi, my conversion) at 2000rpm - how does this compare to the specification for this engine?

Without knowing the spec, I would have judged that to be a shade low for that engine speed. Also, assuming that the pressure switch is ok, it is likely the pressure is dropping as low as 0.3bar (4.4psi) or less - this is definately low. As a comparison the oil presure on my Saab B207R engine is speced as 2.0bar (29psi) at 1000rpm at the crankcase and 0.8bar (11.6psi) at the cylinder head. The specified pressure on the diesel version is 1.0bar at 1000rpm and 4.0bar at 4000rpm.

Some cars are prone to the pick up strainer sludging up which restricts oil pick up, especially at low speed. A single engine flush is unlikely to shift this. First though you need to know if this is the problem. Easy way to check is to drain the oil and look inside the sump cavity with a camera probe. An independant garage should be able to carry out this check for an hours labour plus fresh oil and filter. Since your dealer has gone to the trouble of changing the oil, it seems remiss of them not to have carried out this check whilst the sump was empty and they had it in the air.

Also, whilst changing the pump, did they use an air line to blow down the pick up pipe/gallery to ensure no blockage (assuming you can do this on this engine)?

It could be main or big end bearings, but the only way to know would be to drop the sump and split a couple off and inspect and measure (if the sump can be removed with the engine still in the car). You should eliminate other possible causes before assuming this to be the fault.

Has your dealer offered any advice ref the possible cause? Did they do any investigation other than just changing the pump and checking the pressure?