Intercooler pump relay

[Mark #2]

Intercooler pump relay. If there is anyone here knowledgable on PCM functions and connections to the relay please reply.

I would like to know if grounding the front pin on the low current side of the relay is the same as grounding PCM pin number 70(posted as the correct way to turn on the pump)?

Thanks,
Mark

[L8 APEX]

Yes the PCM grounds the relay coil I would have to look through the book for the pin out#.

[SILVER2000SVT]

I would isolate the pcm with a diode to prevent anything bad from happening to it or throwing a code. It's just a chance that at some point the pcm won't be sending the signal to turn on (like when the truck is off) but you ground the wire so now you are not only grounding the relay but also the output of the pcm. You would think that ford would provide safety circuits to prevent that but you never know. Just my 2 cents. I've done a lot of electrical on cars in the past and I've seen it takes the stupidest little things to freak out the control computers.

[Mark #2]

I would isolate the pcm with a diode to prevent anything bad from happening to it or throwing a code. It's just a chance that at some point the pcm won't be sending the signal to turn on (like when the truck is off) but you ground the wire so now you are not only grounding the relay but also the output of the pcm. You would think that ford would provide safety circuits to prevent that but you never know. Just my 2 cents. I've done a lot of electrical on cars in the past and I've seen it takes the stupidest little things to freak out the control computers.

Thanks to both of you. Jason, you are correct, and everytime I turn the key to the on position I will be grounding the PCM when it is not sending a signal. I don't see how grounding this output would create current flow though?

[SILVER2000SVT]

everytime I turn the key to the on position I will be grounding the PCM when it is not sending a signal. I don't see how grounding this output would create current flow though?

You confused me a little with this last statement. I thought that you were wanted to install some sort of manual switch to turn you intercooler pump on when the truck isn't on? When the truck is on, I think the PCM will always be sending the signal to the pump relay (check me on this though). So like you said it wouldn't have any current flow, not a problem, but it's when the truck is off and obviously not sending a signal and you flip the switch to ground the relay, in addition the PCM output if you don't isolate the circuit. My only concern is that when the pcm is off it might not really be an open circuit in the pcm itself due to solid state technology and output monitoring circuits which may not react well to grounding it.

[Mark #2]

You confused me a little with this last statement. I thought that you were wanted to install some sort of manual switch to turn you intercooler pump on when the truck isn't on? When the truck is on, I think the PCM will always be sending the signal to the pump relay (check me on this though). So like you said it wouldn't have any current flow, not a problem, but it's when the truck is off and obviously not sending a signal and you flip the switch to ground the relay, in addition the PCM output if you don't isolate the circuit. My only concern is that when the pcm is off it might not really be an open circuit in the pcm itself due to solid state technology and output monitoring circuits which may not react well to grounding it.
Plan:
1) Turn on the intercooler pump when the truck is not running.
2) In order to energize the low current side of the relay you have to turn the key to the on position, but the PCM is not outputing a ground to the relay at this time so then
3) Ground the relay.

The plan is not to cut into the wiring harness, but rather tap the relay and take that to ground, so that everytime I turn the key to the on position the pump would be on.

Mark