Having problems with your 1984 Ford F 250 ?

Electrial fuel tank relay- no power to fuel relay

\015 1984 ford f250 electric fuel pump and carberater fuel system. no power from switch to relay.\015 Posted / edited by AnonymousUser on : 12-04-2021

Answers :

There are a zillion cars out there today that use the oil pressure\015\012sending unit as a dual function switch, the first function to send oil pressure\015\012information to the dash gauge or idiot light and the second function being to\015\012run the fuel pump after the car starts. During the start cycle there is a fuel\015\012pump relay that takes over to run the fuel pump. After the engine is running\015\012that relay turns off and the current for the fuel pump is supplied via the oil\015\012pressure sending unit If that relay fails then the car won't start until the oil\015\012pressure is up to three or four PSI.
\015\012The logic is that in a bad accident the engine would stop, the oil\015\012pressure would go to zero and the electric fuel pump would stop pumping fuel\015\012through a possibly ruptured fuel line thus preventing a disastrous fire. \015\012
\015\012When this relay fails the engine will start after the starter motor\015\012has pumped up sufficient oil pressure to send electricity to the fuel pump and\015\012run it. When you turn off the engine the oil remains in the galleys for a short\015\012period of time, typically several minutes for an old worn engine, to a few hours\015\012for a new motor with good tight clearances. Therefore, the engine will start up\015\012again shortly after shutting it off but typically will be relative hard to start\015\012for longer time periods afterwards when the oil pump has to pump the thin warm\015\012oil back into the engine oil galleys. When the engine is cold and the oil is\015\012thicker it doesn't take too long to generate oil pressure and the car will start\015\012up relatively easily, however not as easily as it would if the fuel pump relay\015\012were working. The test is to listen carefully when turning on the ignition key\015\012to see if you hear the fuel pump running - it's in the gas tank so listen there\015\012for a humming noise. If you hear no humming but the car eventually starts and\015\012runs fine, then replace the fuel pump relay.
Repair Help & Product Troubleshooting for 1984 Ford F 250

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