+12v switched power for scavenge pump

[68ChargerJMP]

I know there is a thread on here about needing a fuse tap but I have a little different issue. I'm doing a rear mount turbo and I am running a scavenge pump to get the oil back to the engine. I'm also wanting to use a timed relay to run for 30 sec. once the key is switched off, to evacuate the oil in the return line to prevent pooling in the turbo overnight. I don't want it to be powered on when the key is in "acc", that way I can have my radio on or whatever and not have the pump running. I found a switched +12v under the dash. I used an add-a-fuse on the wiper fuse. Great, doesn't switch power on until key is the "on" position. Problem is, when I turn the key off, it is sending a ground pulse back to my relay and unlatching it instantly. It doesn't seem logical because it is off of the fuse block but I've repeated it 1000 times. If I trigger the relay with any +12v source and remove the trigger, the relay stays latched for 30 seconds and then shuts off like its supposed to. Any ideas how to get around this and still use my timed relay. Thanks in advance.

 

[IBallEngineer]

I know there is a thread on here about needing a fuse tap but I have a little different issue. I'm doing a rear mount turbo and I am running a scavenge pump to get the oil back to the engine. I'm also wanting to use a timed relay to run for 30 sec. once the key is switched off, to evacuate the oil in the return line to prevent pooling in the turbo overnight. I don't want it to be powered on when the key is in "acc", that way I can have my radio on or whatever and not have the pump running. I found a switched +12v under the dash. I used an add-a-fuse on the wiper fuse. Great, doesn't switch power on until key is the "on" position. Problem is, when I turn the key off, it is sending a ground pulse back to my relay and unlatching it instantly. It doesn't seem logical because it is off of the fuse block but I've repeated it 1000 times. If I trigger the relay with any +12v source and remove the trigger, the relay stays latched for 30 seconds and then shuts off like its supposed to. Any ideas how to get around this and still use my timed relay. Thanks in advance.

I get that you tried it 1000 times, but were all attempts from that same power source? Is there another ignition source that doesn't do that, or can you tap the ignition switch directly to avoid that pulse?

As a last resort you can trigger a relay using that ignition source but power your circuit from direct fused battery power. Just like in this diagram which is for fans, but in your case for the timer.

http://www.allfordmustangs.com/forums/attachments/classic-tech/115372d1289469670-electric-fans-relay-wiring-untitled.jpg

 

[68ChargerJMP]

IBall....I'm not sure if there are any more circuits that don't do this. I guess that is my question...I was hoping someone has encountered this before and knew of such a circuit.

That diagram is exactly how I have it wired, except my relay is timed. Problem is it unlatches when the key is switched off, which defeats the purpose of it being timed.

 

[TheDurk]

IBall....I'm not sure if there are any more circuits that don't do this. I guess that is my question...I was hoping someone has encountered this before and knew of such a circuit.

That diagram is exactly how I have it wired, except my relay is timed. Problem is it unlatches when the key is switched off, which defeats the purpose of it being timed.

Well, if the wiper fuse does this, then all the key on circuits on the IG1 circuit will do the same, as far as I can see, and that's all of them, with one exception. I'd suggest you try tapping the IG2 circuit, which only feeds the 10A IGN fuse. It must be different for a reason, and maybe that's it.

 

[68ChargerJMP]

Thanks, will do......if that doesn't work, I may try the fuel pump, or is that on the same leg as the others mentioned?....I don't have any schematics, so it's just t&e.
Is ign2 the box under the hood?.. if so...tried that too....they are always hot.

 

[IBallEngineer]

IBall....I'm not sure if there are any more circuits that don't do this. I guess that is my question...I was hoping someone has encountered this before and knew of such a circuit.

That diagram is exactly how I have it wired, except my relay is timed. Problem is it unlatches when the key is switched off, which defeats the purpose of it being timed.

OK, either I'm not understanding you, or we are having a disconnect.

You say that diagram is exactly how you have it wired, except...

Either it's exactly, or it's not. See my confusion? If it's not exactly, then we can try what I'm saying.

I'm saying use a bosch relay to trigger your timed relay, this way the switched ignition circuit NEVER actually crosses paths with your timed relay, it would be straight battery power turned on and off by the ignition circuit. Is that what you are doing or are you latching your timed relay with the ignition source you described?

opcorn:

 

[68ChargerJMP]

Gotcha. ...I missed the part where you said my timer instead of fans....my bad.
I will try this today and find out...thanks.

 

[TheDurk]

Thanks, will do......if that doesn't work, I may try the fuel pump, or is that on the same leg as the others mentioned?....I don't have any schematics, so it's just t&e.
Is ign2 the box under the hood?.. if so...tried that too....they are always hot.

No, it is a section of the key switch and it feeds the 10A IGN fuse by driver's knee and then the ECM. All the other key-on circuits use the IG1 section of the key switch.

Exactly how the fuel pump is powered varies by year and you don't give yours. Since fuel pump is powered by a relay, it is indeed a different source, although it is triggered by the ECM, which in turn uses the IG2 signal via the IGN fuse and the STA signal via the STA fuse. Of course, [MENTION=102597]IBallEngineer[/MENTION]'s addition of an extra relay will work no matter what key-on trigger you use.

Give me a year and I'll try to post a relevant schematic for you. I have most years but not all.

 

[68ChargerJMP]

Durk.......it's a 97.

 

[68ChargerJMP]

Relay to relay worked...trigger from wiper fuse. Thanks guys.

 

[IBallEngineer]

Relay to relay worked...trigger from wiper fuse. Thanks guys.

Cool...**puts on Clark Kent outfit**

:humble: