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Oil switch

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tombo23

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"can anyone tell me how an oil

"can anyone tell me how an oil switch works, the one that controls fuel pump, is it possible that it can malfunction and stay engaged for few seconds after engine is not running, but ignition switch is returned from start to ignition"
 
The oil pressure switch that o

The oil pressure switch that operates the fuel pump is a normally OPEN type. Oil pressure closes it. Yours could have a weak return spring or gummed up s/sludge.
 
oil pressure does not drop ins

oil pressure does not drop instantly. it bleeds off over a several seconds in an engine in good shape. there is also normally a bypass that allows the fuel pump to run while cranking to aid in starting. the switches used are normally set at around 6 p.s.i. so a few seconds would account for the oil pressure fall off.
 
"do you think cranking alone w

"do you think cranking alone would develop enough pressure and cause the oil switch to engage or would the engine actually have to start, i know the starting circuit also engages the pump but i was wondering like i said when i returned the key to ignition position(with failed start) the pump ran on for few secs so it should be the oil switch thats causing this i guess?"
 
"Most engines will develop a f

"Most engines will develop a few psi of oil pressure if cranking persists for more than 10 seconds or so. That would be enough to trigger the oil pressure switch, But your fuel pump would already be running because the switch is bypassed in start mode, as you have noted.

I can't ever remember hearing my old carbed 4.3 fuel pump running after pausing cranking, but then I don't think I had occasion to pay attention to it.

Rod"
 
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