Lucknow: Special Task Force of Uttar Pradesh Police, the concerned department and the oil companies have sealed a total of 13 petrol pumps which were found to be tampered with in the state capital. The joint exercise by STF and oil companies to check tampering at fuel stations continued today. Three more fuel stations were sealed as evidence of tampering by installing electronic devices was found in the dispensing units last night. Surprisingly, three fuel stations owned by UP Petroleum Dealers Association BN Shukla have been sealed for tampering. Mr Shukla along with his son were absconding after the raids. STF, employees from weight and measurement department and staffers of oil companies conducted the raids. Acting on specific tip-off, sleuths from special task force started checking fuel stations across the city since Friday night. The scale of fraud is huge as out of 25 petrol pumps, which have been examined till now, 13 were found tampered with. Officials said here today that in the coming days, action on people owning the pumps will be taken. A seven-member police team of inspector- and sub-inspector rank-officers has been constituted to probe the entire racket which will be directly monitored by SSP. The team has been taking help of one Rajinder, the supplier of the chips. He was arrested on Friday and is in the police custody. So far, STF has arrested more than two dozen people, majority being petrol pump staffers. The STF team is taking help of the oil companies and has also approached Gilbarco and Midco, the companies which manufacture fuel dispensing units to find out how the hack worked.