21509941 Volvo.Penta Control unit

Stop the engine.
Turn off the start switch or disconnect the battery (starting motor) when maintenance is performed on fuel filters.
Shut off the fuel tank supply valve to the engine.
Unlock the fuel priming pump in order to relieve residual pressure in the fuel system.
Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting, and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids.Refer to Special Publication, NENG2500, "Cat Dealer Service Tool Catalog" or refer to Special Publication, PECJ0003, "Cat Shop Supplies and Tools Catalog" for tools and supplies suitable to collect and contain fluids on Cat products.Dispose of all fluids according to local regulations and mandates.
Remove the used fuel filter.
Clean the gasket sealing surface of the fuel filter base. Ensure that all of the old gasket is removed.
In order to meet expected fuel system component life, 4 micron(c) absolute or less secondary fuel filtration is required for all Caterpillar diesel engines that are equipped with common-rail fuel systems, and for all Caterpillar diesel engines that are equipped with unit injected fuel systems. For all other Caterpillar diesel engines (mostly older engines with pump, line and nozzle type fuel systems), the use of 4 micron(c) absolute or less secondary fuel filtration is strongly recommended. Note that all current Caterpillar diesel engines are factory equipped with Caterpillar Advanced Efficiency 4 micron(c) absolute fuel filters.
Apply clean diesel fuel to the new fuel filter gasket.
Do not fill the secondary fuel filter with fuel before installing. The fuel would not be filtered and could be contaminated. Contaminated fuel will cause accelerated wear to fuel system parts.
Install a new fuel filter. Tighten the fuel filter until the gasket contacts the base. Tighten the fuel filter by hand according to the instructions that are shown on the fuel filter. Do not overtighten the fuel filter. Note: Do not remove the plug in the fuel filter base in order to release air from the fuel system during periodic service of the fuel filter. Periodic removal of the plug will result in increased wear of the threads in the fuel filter base.
Operate the fuel priming pump until a strong pressure is felt on the fuel priming pump and until the check valve "clicks". This procedure will require considerable strokes. Lock the fuel priming pump.
Open the fuel tank supply valve. If necessary, reconnect the battery to the starting motor.
Start the engine according to the normal operating procedures. Immediately increase the engine rpm between 1000 to 1200 rpm with no load. The engine will begin to misfire briefly until air from the fuel filter is purged. No damage to the engine will occur.
Do not crank the engine continuously for more than 30 seconds. Allow the starting motor to cool for two minutes before cranking the engine again.
If the engine stalls during the purging of the air, refer to the Operation and Maintenance Manual, "Fuel System - Prime" for more information.