Since the paint is peeling already,try using a heat gun to loosen the rest!
If it doesnt work you need to sand the grills down to bare plastic (takes time but it will be worth it ).Start with 220 dry sand paper and finish with 400.Then to rermove all sand paper scratches,use wet sand paper,starting with 320 and finish with 1200!
You may be lucky and it may all peel off with heat gun!After you removed all the paint,do as TiagX5 correctly said,use a plastic primer before applying any paint!

Bulldog is the best stuff for getting paint to stick to plastic. I stripped the fau-suede finish from the dash/console of the convertible Viper in my sig, Bulldogged and finished with a metallic charcoal grey Dupli-color rattle can, in 8 yrs and 100k miles in the Florida sun there was ZERO peeling.

nice tip. i will have to stow this one. i have some black over chrome parts that have chipped/peeled over the years for which this will come in handy.

Thanks. I am going to try to sand it. Otherwise I use the bulldog and then paint it black.

May be a bit on the "overboard" side....but you could pull the grilles and take them to a media blasting outfit that uses crushed walnut shell media. It should take the paint out without damaging the plastic.

Just get some Acetone. It'll take the paint off and leave the plastic alone. Just use a rag. Don't soak the parts in it.

And It will set you up to repaint in the same step.

I had spray tinted the tails on my Dodge truck. It got banged up on one of the corners of the bed. After I had it fixed, I had one tinted tail, and a freshie( I wanted them to be the same darkness...) I simply wiped down the tinted one with the acetone, the spray tint came right off, and re-sprayed both. They look great.

Shouldn't be too much different for the grilles.

Thanks for all your replies. I ended up removing and sanding the grills using a 200 sand paper to get get as much of the Silver off as I could and then used SEM Gloss Black over it . Doesn't look that bad and although SEM was a bit more pricey than Dupli-Color I thought it was easier to use than the Dupli-Color for a newbie like me as SEM didn't pool up.

I had plastidip on mine and wanted to re do it so i just dunked the entire grill piece into the solvent tank at work, worked, but some of the original titan color came off

Why would you do that?Plastic dip just peels off ,with no damage to under paint (titan)!Thats the whole point of it:stickpoke

It was really difficult to get it all off from the inside deeper edges:dunno: