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| Joined: | 04-07-2022 |
| Location: | Oregon USA |
| Posts: | 65 |
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I am installing a oil pressure switch to the circuit that runs my fuel pump, with the idea that when there is insufficient oil pressure (<9psi) power will be interrupted to the pump. I have this set-up on another car and it works well, shutting the pump off immediately when I turn off the engine. On the JH however, when I shut the engine off, the oil pressure takes a long time to fall and the pump stays on. I haven't let it run long enough to see how long it would actually take to shut off. (The car is wired with an aftermarket harness and the pump circuit is energized in the "run" position).
My guess is that you are back feeding power to the fuel pump through some subtle loop back path in the wiring or using the wrong source for the power feed. The oil pressure will normally fall to near zero (~5 PSI) in just a few seconds. What does your oil pressure gauge say is happening when you turn off the ignition - i.e. how fast does it fall? What viscosity oil are you running? High vis oil will certainly aggravate this issue. Are you running an oil pressure switch (on/off) or a sender? How many terminals are there on the oil pressure switch (assuming you installed one). What pressure is required to close the OP switch? If it is very low (1 PSI? <shrug>) the pump may run for quite a while. Does your oil filter have an anti drain back valve in it? This will prevent the oil pressure from falling rapidly since oil is not free to move backwards through the filter when the pump stops moving.
My GUESS is that you are feeding power through the OP switch to the pump using the battery (unswitched +12v - usually a brown wire) as your power source. This would be wrong. You must draw your OP switch power from a solid white wire (i.e. SWITCHED +12v) and you must reroute the current power lead at the fuel pump from the pump to the hot side of the starter (not the solenoid, the starter motor). This will do three things: 1. Your pump will only operate when there is oil pressure OR the engine is cranking. 2. Turning off the ignition will immediately turn off the fuel pump no matter what the OP switch is doing. 3. If oil pressure drops, the pump will shut off.
With your current setup, in an accident that stalls the engine you will pump fuel all over the scene of the accident unless you remember to turn off the ignition - potentially causing a fire. You want the pump to shut off in this scenario since you may not be thinking clearly. The downside to this is that the first start of the day may require a few extra seconds of cranking since the fuel pump may need to refill the float bowls as fuel can evaporate from the bowls overnight.
Vance
Last edited on 12-06-2024 09:34 pm by vnavaret