8 posts / 0 new
Last post
awdboosted
Offline
Last seen: 3 months 5 days ago
Joined: 03/07/2015 - 05:49
Adding back low speed fuel pump setup

My setup: Evo IX with Infinity 6 using PNP harness.

After researching, it appears that the low speed functionality was never built into the PNP setup and the fuel pump always runs at full speed. To my understanding, when the ECU grounds the 3rd relay, low speed feature is activated. When not grounded, the pump is on full speed.

I would like to add this back in and I was looking for an open Lowside to do so. Seeing that I don't have AC any more. I was thinking about using Lowside Switch_6. however the description concerns me and I'm not sure it I can use it.

So I have some quesions?.

1. Can anyone advise or have an idea what pin to use?

2. Can you use one pin to trigger two relays? I'm planing on adding a 10 gauge power wire to better power the fuel pump.

 

 

Thank you everyone

AEM_NS
Offline
Last seen: 1 year 1 month ago
Joined: 06/06/2014 - 09:31
What about the description

What about the description concerns you?  Have you actually verified that grounding this third relay actually brings the pump speed down?  I'd do that first before making any wiring changes.

awdboosted
Offline
Last seen: 3 months 5 days ago
Joined: 03/07/2015 - 05:49
Hello AEM_NS,

Hello AEM_NS,

Thank you for replying.

The comment in the box says "inductive load should NOT have full time power." I'm not sure what that even means. lol This would only be active when cruising or at idle.

Per the Evo Diagram. If Pin 55 is not grounded, it will not trigger the low speed feature. I already verified that this pin is not accounted for on the PNP harness.

AEM_NS
Offline
Last seen: 1 year 1 month ago
Joined: 06/06/2014 - 09:31
Inductive loads would be ones

Inductive loads would be ones that use electromagnetic fields to do work; in general these are electric motors, fans and relays.  They usually have two terminals: one power and one ground.  The lowside from the Infinity is providing the ground to the device.  Full time power means 12v is always present at the power pin of the device.  The opposite of full time power would be switched power which means 12v is only present when the ignition switch is on.  One problem with inductive loads is that when switched off, large voltage spikes can be transmitted back into the circuit which can damage a lowside transistor.  To prevent this, a "flyback diode" is used to dump this excess voltage back to 12v.  Because of this diode connection, having full time power at the device means that voltage can be backfed into the Infinity which will keep it powered on after the ignition switch has been turned off.  Thus, when connecting LS6 from a 506 box to an inductive load (electric motor, fan or relay), there should NOT be 12v present all the time otherwise you risk having the Infinity act bad.  FWIW, most relays are not usually wired to have full time (perm) power in OEM usage.  

Looking at your diagram, it seems that the 3rd relay only gets 12v once the 1st and 2nd relays are on and those relays are powered on by the ignition switch.  It looks like you're okay to use LS6 to control the 3rd relay.  Also, I understand that the pin isn't there; my suggestion was to manually ground the relay to ensure that the function works correctly before taking the time to move wires around to make this work.  

awdboosted
Offline
Last seen: 3 months 5 days ago
Joined: 03/07/2015 - 05:49
I follow. Would I be able to

I follow. Would I be able to wire two relays on the LS6 control. Or would that be too much?

 

Thanks in advance

AEM_NS
Offline
Last seen: 1 year 1 month ago
Joined: 06/06/2014 - 09:31
LS6 is rated to 6A.  A relays

LS6 is rated handle up to 6 Amps of current.  A relays coil has about 100 ohms of resistance but with two relays in parallel, the resistance would be halved.  Following Ohms Law of V=IR,  (Volts) = (Current) * (Resistance).  

So, (14 Volts) = (Current) * (50 ohms)...    solve that for current and you get (Current) = (14 Volts) / (50 ohms) ...  in other words (Current) = 0.28 Amps   which is no problem.  I'd say you're good.

awdboosted
Offline
Last seen: 3 months 5 days ago
Joined: 03/07/2015 - 05:49
Thank you for your reply. Way

Thank you for your reply. Way over my head with the math. LOL. I'll take your word for it. yes
 

jeanwill
Offline
Last seen: 3 months 1 week ago
Joined: 05/08/2019 - 22:03
I don't no

I don't no