Pakistan has been hit by a wave of bombings in recent years, most carried out by Islamist militants linked to the Taliban or Al Qaeda who are opposed to the government's support for the United States.
The car bomb went off as the men approached to investigate following a tip-off that a body was in the parked car, said Peshawar police chief Safat Ghayur.
"As the police patrol van reached the spot the vehicle blew up. We lost all the men," Ghayur told Reuters.
Five of the dead were police and three were paramilitary soldiers, police said.
Most of the bomb attacks in Pakistan over the past couple of years have been aimed at security forces, particularly in the northwest, although militants have also attacked politicians and targets with Western connections.
There have been attacks in all major cities.
Last Tuesday, gunmen attacked the Sri Lankan cricket team in the northeastern city of Lahore, killing seven Pakistanis and wounding six Sri Lankan players and two team officials.
Nuclear-armed Pakistan is also struggling with an economy only staying afloat with the help of an International Monetary Fund loan, while its one-year-old civilian government is embroiled in a confrontation with its main rival.
The problems have raised fears about prospects for a country that some analysts fear could become a failed state.