I have a 1996 1.3 HCS-engined Ford Fiesta. It starts perfectly and ticks over fine, but when under load it lacks any sort of power and splutters a lot. I've adjusted the tappets and replaced all the plugs and leads, fuel filter, air filter and the coil pack, but the problem still exists. It also makes a hissing noise from the exhaust. Does any one know what the solution is?