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Roadrunner69

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I have a 98 5.7 I replaced the check valve, the fuel pump and both filters. I only have 12v at the pump while cranking then no voltage when key in run mode. Is this normal, does it run on Ventuari after it starts? I have been running street gas with ethanol (regular grade) for years. I've been told ri stat buying marine gas because it's hi test and no ethanol. I have a rebuilt carburetor ready to go on now but id like to find out if I'm supposed to have 12v constantly when running. I've checked the pick up tube in tank also.
 
No it runs of the ignition circuit once the starter is off, but goes through an oil pressure switch which is a common fail point. I think it is generally located by the distributor and threaded into the block. Should be two wires take connector off and insert a jumper wire see if it works. Alternatively you could test for continuity across the switch while engine is running ( needs 4 psi oil pressure to make the switch).
 
On V6 engines it is Tee'd off at the oil filter location.
The 5.0 may also be at the same location if not on the manifold.
Seems like the oil filter lication would be best as oil pressure is there much quicker then to the manifold when cold...

There may be more than one "sensor/switch"
The oil pressure switch is open/close for the electric fuel pump. Less than around 5 psi and it does not allow power to pump.

A pressure sensor would send a audible alarm if oil pressure is low or none while running or key in run position.
 
kghost said:
On V6 engines it is Tee'd off at the oil filter location.
The 5.0 may also be at the same location if not on the manifold.
Seems like the oil filter lication would be best as oil pressure is there much quicker then to the manifold when cold...

There may be more than one "sensor/switch"
The oil pressure switch is open/close for the electric fuel pump. Less than around 5 psi and it does not allow power to pump.

A pressure sensor would send a audible alarm if oil pressure is low or none while running or key in run position.
Click to expand...

I think on my 5.0 the fuel pump oil pressure switch is by the distributor on The block. I thought the one by the filter was for the oil pressure alarm But I could be mistaken. Either way it’s in one of those two places.
 
Thanks for all the info, guys. I'm going to look more into this Saturday. I'm going to take a look at the ignition switch and now the oil pressure sender. I'll let you know, pray for me!
The kids are getting impatient.
I'm still wondering if that fuel pump should have 12v while running. I can keep it running with a funnel of gas in the line held up above the motor with no power to the fuel pump.
 
Last edited:
Roadrunner69 said:
Thanks for all the info, guys. I'm going to look more into this Saturday. I'm going to take a look at the ignition switch and now the oil pressure sender. I'll let you know, pray for me!
The kids are getting impatient.
I'm still wondering if that fuel pump should have 12v while running. I can keep it running with a funnel of gas in the line held up above the motor with no power to the fuel pump.
Click to expand...

not the sender This is the oil pressure switch should have two wires connected to it. The sender for the oil pressure gauge has a single wire.

and yes the fuel pump needs 12 v when in run position. When starting it gets 12 v off the starter motor, when the key is put in run after the engine starts it gets 12 v off the sample circuit (purple wire) that gives 12v to ignition (+ side of coil) and choke, it just goes through an oil pressure switch so power To the fuel pump gets killed if the engine is not running and thus producing oil pressure. This prevents the fuel pump from running if the engine stalls out or if the key is inadvertently put in run... or if the oil pressure switch is broken... likely your scenario.
 
That was ignition circuit not sample circuit... auto correct is killing me. Let us know how you make out
 
I'll let you know. Im thinking about this and I always change the oil in the fall and could have hit the wires on the oil switch. Is there a automobile switch no. I could use to get this?
 
They are not that much I think OEM is like $30 aftermarket like $20? Put your serial number in the parts section on this site will come up with both OEM and aftermarket options
 
The sender and also the switch are both next to the oil filter. I did break off a terminal off the switch. I soldered a wire back to it and reattached it. It works with air pressure checking continuity. Thank you again for the info.
 
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