Have you tried a new relay? You will need to check the signal at the relay to see if the ECU is sending out the ground to turn the relay on. If you are getting the ground from the ECU replace the relay, if not check it at the ECU. If you have no ground at the ECU the ECU is bad. Once you get it figured out run a new relay right next to the pump in the trunk with bigger gauge wire and use the output from the OEM relay to activate the new relay. My duty cycle decreased by 10-15% when i did this, battery is in the trunk so it makes it real easy.