Fuel Pump Relay Question
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Fuel Pump Relay Question Question, I made my standalone harness and am ready to hook it up to my engine. I do have all orange and pink wires hooked together. When I give this 12 volts, I noticed that my fuel pump relay wire (Dark Green wire) has a constant 12 volts. It doesn't do a priming where it has 12 volts for couple seconds and then shuts off. Is this because all the wires requiring power are hooked together, or is something wrong with my PCM? Thank you.
Hard to say but I would start by applying power properly. The orange wires need constant 12 volts so hook them up and then hook the pink wires up through a switch so you can turn it on and off like an ignition will. Make sure you've got the ECM grounds grounded as well.
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if you have all the orange and pink wires hooked together, you may see some strange behavior. orange is constant power as in straight to the "+" terminal on the battery. Pink is ignition, which is only live when the key is on. The ECM will run the fuel pump for a few seconds when ignition (pink) toggles from off->on. If you have all pink and orange wires connected, that transition may not be properly detected by the ECM
As I recall there are wires/contacts that need 1) 12V+ all the time; 2) 12V+ when the ignition switch is in the run/on position; 3) 12V+ when the ignition switch is in the 'start' position. Can't imagine good things would happen if all those were just attached to a 12V source simultaneously.
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I tried hooking the orange to constant 12 volts, then gave the pink wires 12 volts. I get the same thing the fuel pressure wire reads constant 12 volts. The only thing I can think this is happening is because I don't have the connections to the sensors. Will try and connect the harness to the engine and see if that makes a difference.
Are you just checking this with a meter? These controls aren't like actual switches in the ECM they are open collector outputs which means you could see voltage because they don't exactly shut completely off as a switch would, but they shut off enough to limit current flow to control a relay. If you are still having the issue hook up a relay and see if it's reacting correctly. The ECM MIL (check engine light) does the same thing with an LED on it because they never really limit current completely so the LED is always dimly lit until the open collector closes then the LED goes bright.
Last edited by 1964SS; Mar 5, 2020 at 09:57 AM.
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Are you just checking this with a meter? These controls aren't like actual switches in the ECM they are open collector outputs which means you could see voltage because they don't exactly shut completely off as a switch would, but they shut off enough to limit current flow to control a relay. If you are still having the issue hook up an relay and see if it's reacting correctly. The ECM MIL (check engine light) does the same thing with an LED on it because they never really limit current completely so the LED is always dimly lit until the open collector closes then the LED goes bright.
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