Is the fuel sending unit separate from the fuel pump or are they both part of the same assembly. My pump is fine but my sending unit is bad. I have a 93 SC 400.

 

The sending unit is technically the plastic shell that holds the pump which is incorporated with the sensor for fuel level. That is at least the way they'll sell it as far as parts go. So I'm guessing your fuel level isn't correct on your gauge on the dash?
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I thought the 400's fuel level sending unit was the part mounted to the rear of the tank (reached from the trunk) rather than built into the fuel pump bracket. I have switched out my fuel pump and don't recall a float -- but it's that way on other cars.

 

The sending unit is seperate