Detroit Diesel — External And Internal Low Pressure Fuel Leak Test
Testing & diagnosis · Fuel system
From a Detroit Diesel service manual — check it applies to your exact model before use.
Before you start
- PRESSURIZED AIR AND FLYING PARTICLES - To avoid injury to eye or face, wear a face shield or goggles when conducting a pressure test.
Procedure
- Shut off engine, apply parking brake, chock wheels, disconnect vehicle battery power, and perform applicable safety steps.
- Remove fuel feed and return lines from fuel filter module.
- Install J-48710 fuel pressure test kit onto module.
- Insure shutoff valve (2) is in the OFF position.
- Turn regulator (1) counterclockwise until it stops; set to zero pressure.
- Connect to shop air pressure.
- Turn shutoff valve to ON position.
- Turn regulator clockwise to increase fuel system pressure to 75 psi.
- Once pressure stabilizes for one minute, turn shutoff valve OFF and disconnect shop air.
- Wait 30 minutes; pressure should not drop over 30 minutes.
- Reconnect shop air and turn on valve.
- Spray all connectors, fittings, and braided hoses with soapy solution; repair leaks if found.
- Remove oil fill cap, listen for internal leaks. If heard, remove rocker cover; if no injector leak, remove oil pan and check fuel pump gear.
- Install cooling system pressure tester. If coolant pressure rises and fuel is in coolant, replace fuel cooler behind fuel filter module; else retest.
Tools required
- J-48710 fuel pressure test kit Amazon
- shop air pressure Amazon
- soapy solution Amazon
- cooling system pressure testing tool Amazon
- face shield or goggles Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 75 psi
- 30 minutes
Source: Detroit Diesel service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.