Replacing Fuel Pump Check Valve (CIS, CIS-E, and CIS-E Motronic)All CIS, CIS-E, and CIS-E Motronic fuel pumps have a check valve at the outlet to help maintain pressure in the fuel system, particularly as an aid to hot starting. Failure of this replaceable check valve is one of the most likely causes of low residual fuel pressure and difficult hot starting. For information on testing residual fuel pressure, see 5.5 Fuel Pressure Tests and Specifications (CIS) or 6.6 Fuel Pressure Tests and Specifications (CIS-E and CIS-E Motronic). The location of the pump check valve is shown in Fig. 4-15. To replace it, clean and disconnect the fuel line as described above in Replacing Fuel Pump. With the line disconnected, the check valve can be removed from the pump. Use new sealing washers for both the check valve and the fuel line union. Torque both parts to 20 Nm (15 ft. lb.). On cars with CIS-E and CIS-E Motronic, there is an additional check valve at the fuel reservoir, in the supply line from the transfer pump. This valve is also replaceable. It should be replaced if hot start problems persist, even though the residual fuel pressure meets specifications. This fuel reservoir check valve is shown in Fig. 4-16. Remove the line from the transfer pump, as shown, to gain access to the valve.
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