Oil pressure question

aearch

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SPEAKING OF OIL UNITS
BILL BOUGHT ONE THAT HAS 4 WIRES AND I LOOKED IT UP AND IT SEEMS IT INTERUPTS
THE FUEL PUMP LINE AND TURNS OF THE PUMP WHEN NO OIL PRESSURE
IM THINKING WHY BOTHER IF U HAVE NO OIL
YOUR TOAST ANYWAY
AS ITS ONLY THE OIL PUMP THAT CAN DO THAT AND THEY NEVER FAIL
OK
 

Honolulu

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What I've read is that you want about 10 psi for each 1,000 rpm, up to about 80 psi (8,000 rpm). This from the days where my aircooled VW and 2002s showed a flickering oil pressure light at idle. Cold oil can have surprisingly high pressure, which disappears when the engine is hot. It depends a lot on the viscosity index of your oil, which is a lot more stable now than it was in my old-time dino-juice Pennzoil 30-weight days.

Oil thread, anyone?
 

gazzol

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SPEAKING OF OIL UNITS
BILL BOUGHT ONE THAT HAS 4 WIRES AND I LOOKED IT UP AND IT SEEMS IT INTERUPTS
THE FUEL PUMP LINE AND TURNS OF THE PUMP WHEN NO OIL PRESSURE
IM THINKING WHY BOTHER IF U HAVE NO OIL
YOUR TOAST ANYWAY
AS ITS ONLY THE OIL PUMP THAT CAN DO THAT AND THEY NEVER FAIL
OK
The purpose of the system you are describing is not to cut the fuel pump if there is no pressure (which it will) but rather to only switch the fuel pump on once there is oil pressure, which is a good idea but the down side is (there always is one isn't there! ) that if the engine gets tired and can't develop enough pressure at cranking speed it will never start at all unless you fit a timer relay which runs the pump for a few seconds when you turn the ignition on.
 

Mike Goble

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The purpose of the system you are describing is not to cut the fuel pump if there is no pressure (which it will) but rather to only switch the fuel pump on once there is oil pressure, which is a good idea but the down side is (there always is one isn't there! ) that if the engine gets tired and can't develop enough pressure at cranking speed it will never start at all unless you fit a timer relay which runs the pump for a few seconds when you turn the ignition on.
If you need the fuel pump to run while you're cranking the starter you can simply use an oil pressure switch with Form C contacts, as described in this article.


 

Honolulu

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Curious layout. I'd have thought the fuel filter would be downstream of the pump, on the pressure side, so as not to starve the pump if there's "some" crud in the filter.

As shown it does protect the pump, in case it needs it.

What is/are "Form C" contacts? All the bimmer oil pressure switches I've ever seen are single wire.
 

Mike Goble

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Form C contacts are like a single pole double throw switch. One set of contacts is normally closed and the other is normally open. Upon actuation, in this case when the oil pressure is sufficient, the closed one opens and the open one closes. Most oil pressure switches are Form B, closed until the oil pressure is good.



Many aftermarket fuel pump manufacturers recommend a filter before the pump. If you don't have a sock on the pickup you want a filter before the pump. The BMW in-tank pumps have a filter built into the pump.
 

Ohmess

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I have one of these, which runs the fuel pump for three seconds when you turn the ignition to position two, and which cuts off fuel flow if you don't have a signal from the ignition coil:

 
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