- Disconnect the fuel feed manifold from the rubber attached to the injector to be checked and plug the end (use a flexible pipe, inside diameter = 7 mm, length = 50 mm, plugged at one end. Ensure fuel-tightness at the plug and on the fuel-feed manifold by «quick-acting» clips * ). the circuit as shown above. If the pressure does not drop : the injector being checked is leaking and must be replaced.