Thanks Rod. I learn something new every day here. it’s always a pleasure.
Now my little pea brain will go bananas trying to figure out why they did that.
Some Ford trucks /vans used oil pressure switches for their fuel pump shutoffs This was on non-fuel injected gas models w 351W, 370, 429 and460 Holley-carbed setups. Ford got rid of the eccentric driven pump and went electric way before fuel injection came in…The 1960s for heavy truck. I always like electric…those eccentrics and mechanical pumps waste alot of gas doing nearly nothing but making noise and leaking oil.
My '72 Vega had the fuel pump circuit that required sufficient oil pressure in order to stay enabled. It protects the engine by shutting the fuel supply off if the oil pressure disappears. I always thought it was a great idea. Judging from the posts we get here, every car should have this feature.
It protects the engine by shutting the fuel supply off if the oil pressure disappears
It’s also a safety feature. If the engine doesn’t start, the fuel pump shuts off. In the event of a serious collision, if the engine stops, the fuel pump does too. Had a car t-boned right in front of my house. The car came to rest on my front lawn, engine stopped running but fuel pump was still running, spewing fuel from severed line. Had to reach in and shut off the key before the emergency rescue people showed up. Ford used inertia switches to accomplish the same thing.
Nasty!
Personally I’m in favor of inertia switches as well. Were a car to go bottoms-up and the engine still keep running (not inconceivable with multiport injection or direct injection), it would be better to have the engine shut down. While the gas tank is allegedly protected from spilling by the “spill valve”, I’d prefer to have the engine shut down were I in the vehicle. The less there is going on mechanically is the less chance of fire.
My 1975 Civic had a relay between the oil pressure sender and the electric fuel pump.
I don’t think this type of scheme would always protect the engine from lack of oil on a carbureted car because it can take awhile to empty the float bowl.
Truth is that in an upside down carburated engine the float would keep the needle valve closed just due to gravity anyway. And with the circuit from the bowl to the venturi orafice then being above the fuel in the bowl, drawing from the air pocket, the fuel supply would stop and the engine stop running.
Modern engines with multiport or direct injection can run upside-down fine…until the loss of lubrication from the oil pickup screen being high & dry lets them tear themselves apart inside until they seize.