VW Transporter trouble

G'day folks,

My mate's got a 1988 VW Transporter 3sp Auto and he's having some trouble with the engine cutting out. I followed him from the mechanics today and noticed that every time the engine loses power (cuts out) is smokes like hell. Like a burning oil smell. This happens intermittently. So he has to pull over, rev her up a bit, then keep on going. It can go great for a long time, no smoke, or it can cut out every 5 mins. The mechanic diagnosed the problem as being a blocked catalytic converter, but fixing this made no difference. In fact it's only become worse. Can't give you the mileage as the clock only goes up to 99,999 km. Past that, who knows. Any thoughts?

Thanks guys.