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CRUSADER 502 xli no start

L

lugnutdan

Contributing Member
New post I have a 502 xli witch is not getting 12 volts ,when I hit start button 12 volt comes on to the fuel pump ,then shuts right down
engine still cranks and I get spark, checked both relays good, switched oil alarm sending unit no change, I then cleaned distrbuor cap engine then started
all was good ,next day again no start, replaced rotor and cap. Again no 12 volt can anyone give some direction
 
Based on checking the manual library (mercruiser only for a 502 TBI unit - crusader, like production merc stuff, typically used the recommended GM factory configuration) the ECU controls the fuel pump via the fuel pump relay...the fuel pump fuse protects the relay and pump. when the key is turned to RUN, the fuel pump should come on for about two seconds. if it does, then you need to see that the ECU keeps the relay engaged with the engine running...could be an intermittent (dirty connection)...how did you verify the relay was "good"?? The GM provided harness provides the +12VDC, for the fuel pump, via a 20 amp fuse, to the fuel pump relay terminal 30. When the relay turns on, the current flows from terminal 87 to the pump...you can jump these two terminal, TEMPORARILY, to see if the fuel pump relay is intermittent (assuming the ECU control wire is good)...
 
I switched relays with a new one ,and when key is turned on 12 volt comes on for 2 seconds then clicks off.thanks for the help.
 
Then that means the basic circuit is good, assuming the pump makes adequate pressure...(assuming the "...when key is turned on 12 volts comes on for 2 seconds..." refers to the measurement across the fuel pumps terminals).

So the remaining questions are: 1)dos the fuel pump make adequate pressure and 2) does the pump run after the engine starts? (the ecu looks for pulses from the distributor to determine the engine is running keep the fuel pump running.)
 
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