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HungryPillow
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AEM Fuel Pump + 20 Amp Relay Kit

Hi AEM,

I hope this is the correct forum to post in as I couldn't find one specific to Subaru or the relay kit.
 
I recently purchased the AEM 50-1215 fuel pump and 30-2062 amp relay wiring kit. I'm in Singapore and my mechanic does not speak much English so I'm having a difficult time explaining the diagram to him.
 
From what I can see in the instructions that came along with the relay kit:
 
Terminal 30 goes to the battery
Terminal 87 goes to the fuel pump
 
Terminal 85 and 86 are what I'm not too sure about. Does 86 go to the ignition and 85 is just a ground? The instructions diagram says low side driver in ECU. What does that mean? Could you explain to me where exactly these two terminals should be connected? And the instructions also say 85 and 86 are interchangeable?
 
My car is a 2006 Subaru Legacy GT. Thank you and I appreciate your help.
AEM_NS
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As the instructions show, you

As the instructions show, you can do it one of two ways.

You can either find the trigger wire that triggers the stock fuel pump relay which should be a ground signal and use that to ground 86. If using a ground, you need to supply power to 85.  The other way to do it would be to use the output from the stock fuel pump relay which should be 12v and use that to power 85.  You'd then ground 86.  

Lowside means ground and highside means 12v.

HungryPillow
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Hi,

Hi,

Thank you for the reply. So in your example I could use the ignition on/off for the power to 85 and then ground 86 anywhere? Or it has to be ground at the ECU?

AEM_NS
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You should not use the

You should not use the ignition switch to activate the relay. This would make the pump run when ever the ignition is on. This isn't safe. Use either the ground trigger to the stock fuel pump relay or the 12v output from the fuel pump relay. If using 12v from the stock fuel pump relay to 85, you can ground 86 where ever.

HungryPillow
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Hi,

Hi,

Thank you for the reply. In the diagram in the instructions, it shows Terminal 86 going to the Switched 12V Power (Ignition) so I just assumed that's where the wire should go. My current fuel pump when you turn the key to the on position you can hear the fuel pump priming (there's a brief whining sound for maybe 1-2 seconds), does this not mean it's on?

Sorry if these are stupid questions, this is all kind of new to me :)

AEM_NS
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The diagram in the

The diagram in the instructions shows that a lowside ground signal from an ECU is what's turning the relay on, not the ignition switch. So in your case, you need to let the ECU switch the relay on and off, not the ignition switch. The ECU controls when the fuel pump is on or off including prime. If you use the ignition switch to control the relay then you will lose this functionality. The fuel pump will be on whenever the ignition switch is on which is not safe. If you pay close attention to your car you'll see that besides initial key on prime, the fuel pump is only running when the engine is running.

HungryPillow
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Hi,

Hi,

OK, I think I understand now. I guess my last question would be how do I find the lowside ground signal from the ECU? Do I actually need to remove the ECU for this or do I just need to find the wire coming from the ECU that controls the fuel pump?

AEM_NS
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A good tool to use would be a

A good tool to use would be a service manual that has a wiring diagram. You could also locate the factory fuel pump relay, remove it and then identify which wire goes to ground when you turn the ignition switch on.

HungryPillow
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OK great, thanks so much for

OK great, thanks so much for your help!

HungryPillow
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Hi AEM,

Hi AEM,

I managed to get everything installed today and everything seems fine. The pump is very quiet and working great!

I just have a quick question about the relay. My mechanic installed it just underneath the dash near the steering wheel (RHD car), and everytime I get on the throttle maybe 40-50% and around 2-3K RPM when the boost starts to come on, I can hear a series of clicking from what I think is the relay. Then as I keep accelerating the clicking stops. Is this normal operating behaviour? Thanks.

AEM_NS
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Not sure how I can help you

Not sure how I can help you with this. You hear clicking that you think might be the relay but you don't really know if that's what it is. I think it's fairly obvious that a relay should either just be on or off and not cycle or starting clicking unless you're triggering it by something that's cycling on and off for some reason. It sounds like you and your mechanic have some troubleshooting to do.

HungryPillow
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Hi AEM

Hi AEM

Did some troubleshooting today as well as some data logging. The clicking is definitely from the relay and it seems that it only happens when the duty cycle of the fuel pump first hits 100%. So I will step on the accelerator pedal, wait for the RPM to climb to maybe 3K RPM or so and boost starts to come on, then when the duty cycle on the fuel pump goes from 66% to 100% I can hear and feel the click from the relay. It's a fast click of maybe 4-5 times. Then it stops as I keep acclerating and there is no more clicking until the next time the duty cycle of the fuel pump hits 100%.

Could this be a faulty relay or is it normal? I'm using the AEM 50-1215 340LPH fuel pump on my car. We also double checked the wiring to the relay is as you suggested, 30 is direct to battery, 87 direct to fuel pump, 85 to fuel pump switch line from the ECU, 86 to ground.

Other than the clicking sound the car is running fine, I managed to solve my lean issue during boost and there is no knocking at all even at WOT all the way to redline.

AEM_SB
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What model year is this

What model year is this Subaru? Did you add the 50-1215 as a second fuel pump, or is it replacing the original Subaru fuel pump?

 

The stock ECU on some Subaru vehicles connects to a Fuel Pump Control Module which is basically a high-speed transistor (not a simple relay). With this setup, the ECU sends a high-frequency duty cycle such as 'on for 33% of the time and off for 67% of the time'. That high-frequency signal will switch on/off and on/off many times per second. My guess is whaever duty cycle the ECU sends to that module for low RPM and low boost is so low that the AEM relay doesn't turn on. At high RPM and boost, the higher duty cycle is enough to turn on the AEM relay and you hear it click when it is transitioning from 'too low' to 'high enough' duty cycle. Ideally, the AEM relay kit should not connect to the stock ECU's duty cycle control signal; the high-speed clicking sounds you hear will make the relay wear out more quickly than normal.

 

Hope that helps,

SB

HungryPillow
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AEM_SB wrote:

AEM_SB wrote:

What model year is this Subaru? Did you add the 50-1215 as a second fuel pump, or is it replacing the original Subaru fuel pump?

 

The stock ECU on some Subaru vehicles connects to a Fuel Pump Control Module which is basically a high-speed transistor (not a simple relay). With this setup, the ECU sends a high-frequency duty cycle such as 'on for 33% of the time and off for 67% of the time'. That high-frequency signal will switch on/off and on/off many times per second. My guess is whaever duty cycle the ECU sends to that module for low RPM and low boost is so low that the AEM relay doesn't turn on. At high RPM and boost, the higher duty cycle is enough to turn on the AEM relay and you hear it click when it is transitioning from 'too low' to 'high enough' duty cycle. Ideally, the AEM relay kit should not connect to the stock ECU's duty cycle control signal; the high-speed clicking sounds you hear will make the relay wear out more quickly than normal.

 

Hope that helps,

SB

 

Hey SB,

Thanks for your reply. My car is a 2006 Subaru Legacy GT. The 50-1215 replaced the original pump and there is no second fuel pump.

If that's the case with the stock ECU's duty cycle control signal, where should the relay connect to ideally? And if I leave it as is is there any safety issue besides wearing out the relay more quickly than normal? Thanks.

AEM_SB
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That's interesting. From this

That's interesting. From this side of my computer screen, I can only make educated guesses based on the info you provide. I can say that the relay should click on once when the engine starts running, then stay on (without clicking) while the engine is running, and then click off after you turn off the ignition switch to stop the engine. There are other things that could cause a relay to click, such as a wiring connection that is intemittently losing contact. If your multimeter has a frequency measurement mode, checking the frequency of the ECU's fuel pump control signal is a good way to confirm it's a duty cycle type of signal. For a 2006 I think there's a good chance it will be.

Assuming you have the relay connected to the stock ECU's duty control signal, the main concern is if the relay wears out and fails at an unlucky time. If the relay fails and turns off at low RPM, there's not much load on the engine so it's not a big problem for fuel pressure to slowly bleed down to zero. If the relay wears out and fails at high RPM and high boost, the engine will likely run lean for a little while due to low fuel pressure before it shuts off completely.

HungryPillow
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Hey SB,

Hey SB,

After some digging and researching you are correct, my car does have a FPCM and uses a duty cycle type of signal.

What would you suggest I do in this case? Is there any way I can still get the relay to work properly with this setup? My car has started to throw a CEL code P0230 - Fuel pump primary circuit.

AEM_SB
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Unfortunately, we're not

Unfortunately, we're not familiar with how your vehicle's stock ECU interacts with the fuel pump control module. I happen to know a little about the duty cycle signal because some of our older standalones for the 2004-2006 STI needed to mimic that in order to run the fuel pump. There is at least one feedback wire going back from the fuel pump controller to the ECU, we didn't need to use this on a standalone replacement ECU. 

I imagine you're not the first person to upgrade the fuel pump on a Subaru, my advice would be to find others who have successfully run similar power and see how they did it. You may need to keep the fuel pump connected to the OEM fuel pump control module in order to avoid faults, and simply upgrade the wiring that supplies that module with 12V and ground. Again I need to emphasize that I'm not familiar with Subaru reflash tuning so you should find someone with more experience making power on your vehicle.

 

 

AEM_NS
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Side note - knowing that your

Side note - knowing that your factory fuel pump is controlled by a variable duty cycle control is very important if trying to add in a on/off relay. Standard relays are not designed to be pulse width modulated. They're designed to be used as on/off only. If you had mentioned that your stock pump was PWM'd, I wouldn't have suggested wiring it using the factory pump triggers.

HungryPillow
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Hey guys,

Hey guys,

Sorry for the late update, but after some digging around and researching on the Subaru forums I managed to find a diagram that people have previously used to upgrade the wiring. I printed it out and asked my mechanic to follow it and everything seems to be working great now. The clicking sound from the relay is gone and so is the CEL. Thanks for all your help! I attached the diagram in case anyone in the future is interested in doing the same thing.

 

AEM_NS
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Thank you for the follow up.

Thank you for the follow up. Glad everything is sorted now.