Vauxhall nova 1.5 turbo diesel engine?

This is the iszuzu engine, The car was running fine but a service was due. I asked around motorfactors for a service price i.e glow plugs, fuel filter, air filter,oil and oil filter, but they asked if the plugs was a 5V or 11V? i did'nt know so i said i would take one of them out and get the details of it. Thats now my problem as i put the glow plug back in and the car turns over but fails to fire up! Any help would be so appreciated
thank you Stefan