Carb Problems?
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Joined: Jan 2001
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From: Virginia
This whole thing is for safety, but there are tons of hot rods and old dump trucks running around without this safety feature. It verfies the engine is actually running before letting the fuel pumps run.
The other part of the circuit I described bypasses all this and powers the pumps while the starter is energized. As soon as you let off the key, then system reverts to the relay system. If you have oil pressure, then it sends power to the pumps. If you don't have oil pressure, but leave the key on, then it assumes the engine has quit and it stops the pumps.
They have a legitimate reason for this. The one scenario I use is if you are in a accident and the fuel line is damaged. You are knocked out, so you leave the key on, so the pumps are still running, and they pump fuel all over the accident scene since the fuel line has been busted. It would not be a good thing in any case, but that's one reason why they interlock the pumps with the oil pressure of the engine.
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Freshman User
Joined: Apr 2014
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The oil pressure switch? Get a new one. If you need to run the truck, just jump the wires together for now and run it.
This whole thing is for safety, but there are tons of hot rods and old dump trucks running around without this safety feature. It verfies the engine is actually running before letting the fuel pumps run.
The other part of the circuit I described bypasses all this and powers the pumps while the starter is energized. As soon as you let off the key, then system reverts to the relay system. If you have oil pressure, then it sends power to the pumps. If you don't have oil pressure, but leave the key on, then it assumes the engine has quit and it stops the pumps.
They have a legitimate reason for this. The one scenario I use is if you are in a accident and the fuel line is damaged. You are knocked out, so you leave the key on, so the pumps are still running, and they pump fuel all over the accident scene since the fuel line has been busted. It would not be a good thing in any case, but that's one reason why they interlock the pumps with the oil pressure of the engine.
This whole thing is for safety, but there are tons of hot rods and old dump trucks running around without this safety feature. It verfies the engine is actually running before letting the fuel pumps run.
The other part of the circuit I described bypasses all this and powers the pumps while the starter is energized. As soon as you let off the key, then system reverts to the relay system. If you have oil pressure, then it sends power to the pumps. If you don't have oil pressure, but leave the key on, then it assumes the engine has quit and it stops the pumps.
They have a legitimate reason for this. The one scenario I use is if you are in a accident and the fuel line is damaged. You are knocked out, so you leave the key on, so the pumps are still running, and they pump fuel all over the accident scene since the fuel line has been busted. It would not be a good thing in any case, but that's one reason why they interlock the pumps with the oil pressure of the engine.
Senior User
Joined: Jan 2015
Posts: 383
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From: Stockdale, Tejas
the switch (meaning the cut-off switch mounted at the back of the oil pressure sending unit switch) yeah thats toast, change it and your good, or keep running like your are, however heed Franklin2s warning, accident = pumps still running= whatever gas you got in the tanks is coming out
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