Cadillac Repair: Fuel Pump, cadillac fleet, fleet wood

Question
I have a 88 Cadillac Fleet-wood 4.5L The car was starting fine a few months ago. During the time it sat up the battery went down. I put a fully charged battery in and tried to start the engine, and it turned over fine, but would not start. I checked to see if it was getting fuel, but the injectors was not showing signs of fuel. I then went to the gas tank and had a person turn the switch without starting the engine and the fuel pump did not whine. I change the relays around under the passenger side panel still nothing. I changed the fuel pump new a few years ago, and have not driven the car much since. The fuel pump gauge is blinking "E" when I put plenty enough gas to start. Is this a bad pump, or sending unit. Please advise. Sorry for such a long statement, but I wanted you to have all the information that would assist you in your response. thanks Larry Brevelle

Answer
Hi Larry, Thank you for all the background info. It is all important in knowing the history of the car and with it I can better give some tests to do.

     Lets start with the flashing "E" first. What happened back when this car was built was the sending unit resistor board wire wasn't made for the ethynal gas such that it would warp the board in places and then when the gas level changed it could go from 3/4 to empty to 3/5 to empty to 3/8 to empty...or something like that. There was a bulletin out that described this problem and the sender part was redesigned 3 times for 1 model year because of it. The repair was to install the updated sending unit for the car and the gauge would be back to reading normal again.

     As for the fuel issue if a vehicle isn't run very often that is hard on some systems. Also some fuel pumps are made better than others and like I explained about the ethynal it could damage the pump also. Since you substituted relays I would like to think that isn't the problem. To verify that the relay is good and the computor is controlling the relay you would need to disconnect the sending unit connector back by the gas tank, place your voltmeter on the power and ground wires to the pump, turn the ignition key on but don't try to start the engine and if everything is working correctly you should see battery voltage for 2 seconds and the turn off. If that happens and you don't hear the pump run at all then then pump has gone bad. If the pump should run then you really should screw a fuel pressure gauge onto the fuel rail schrader valve and see what it is. The spec is 9-12 psi but if it isn't more to the 12 side then the pump is getting weak or the fuel filter is restricted.

    If you determine that the pump needs to get replaced then it would be a good idea to replace the pump, strainer inside the tank and the in-line fuel filter.

    Hope that helps and let me know if you have anymore questions. Bill