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Old 08-16-2013, 11:24 PM   #1
reid-o
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Join Date: Dec 2005
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Default How to test pump or controller FPC

AEM EMS series 2

I was recently fighting strange lean conditions in traffic that were never there before. I thought it was just IAT (we're talking 1.5 hours in hot traffic), but it didn't make sense to me to increase fuel as temps rose. After 2 months of having the same condition, the day before yesterday my car stalled on the road and I couldn't get it started. Battery and alternator checked out fine. I had to get a push to the side of the road. As soon I got back in the car, it started but ran lean like before.

Yesterday I got stalled on the freeway but managed to pull to the side. This time it was clear on ignition turn that the Walbro (255) wasn't priming. I didn't have any tools with me but had my laptop. Voltage was fine. Starter motor cranked with plenty of juice, but the pump would not prime. It's usually loud. I had the car towed and when it got back home, I looked into enabling the fuel pump controller. I'm assuming the pump is just bad from driving in traffic and being on at 100% all the time. Even when I got the car home, the pump would not prime.

The AEM can control the FPC. I had a spare fuel pump so I just wired it in outside of the tank to see if my settings worked for controlling the FPC. I mapped it to TPS at first just to see. it worked fine. I ordered a 300lph pump and it's on its way. I moved the duty up and down and I could hear the whine get louder and softer.

Here's the strange part. This morning I decided for kicks to see if the pump would prime. I heard a sound for a .5 second (it's supposed to prime for 2). I tried 3 times and same thing. Then I broke out the laptop and disabled the PW settings I set it to run 100 it all the time. Boom the pump primed and it sounded like how it usually primes. I'm a bit worried now if I have 2 issues or 1. Is the FPC bad? Is the pump bad? Or is it possible that both are bad? How could I check? The car started right up and drove fine. I don't have a fuel pressure gauge to see the pump output. Is it possible for the FPC to work intermittently? The pump is on its way, so that's getting replaced. Anyone have any diagnostic ideas other than to just replace the pump and hope for the best? I figure that I probably caused the pump failure by running low on gas and running it 100% all the time. As for what happend this morning, I don't know how to figure out if the FPC or a relay is going out when it's running fine now.
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Old 08-16-2013, 11:30 PM   #2
reid-o
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I'm hoping that the pump just decided to prime becuase of the cycling, but after searching I found a lot of people having to replace their FPC.
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Old 08-17-2013, 12:36 AM   #3
dstroy
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Just get the fuelpro if its your FPC, I got one recently and jockeygolfs has one too. Works like a charm, and has a higher amperage rating than the stocker.
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Old 08-17-2013, 12:40 AM   #4
dstroy
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You can see if your FPC is going bad if you have an o-scope, or access to one. The pwm waveform distorts or isn't present at all until the duty cycle is increased. It happens in all fet based pwm circuits eventually, the transistor gate breaks down. Happens faster because you're running a pump that draws more amperage than the stock one.
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Old 08-17-2013, 03:43 PM   #5
reid-o
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Thanks


I've asked to borrow a scope from a friend.
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Old 08-20-2013, 09:21 AM   #6
dstroy
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Did you get it figured out? Hopefully it was just your pump going bad from running 100%DC since that's cheaper than a new FPC.
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Old 08-21-2013, 05:25 PM   #7
reid-o
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I replaced the pump last night while my friend checked out the fpc. He said he couldn't see anything wrong with it, but we did notice that fuel pump relay was rather hot after running for ten minutes. I read 13.5v on the old relay at the fuel pump harness in the trunk with fpc still connected and ECU commanding 100% with the car idling.

My friend suggested checking the resistance/load on the relay, but I elected to just hardwire in a new relay with 10 gauge to bypass the fpc for the moment using the old relay to trigger. I may change the trigger to use the 5v from the ecu. I ordered the fuelpro in the mean time and plan to trace if there's a short while I wait. Even with the old relay carrying no load, it gets pretty warm so there's something wrong. The new pump dw200 is silent which is good, but its now a bit harder to listen for pump operation on the road. When I stalled, the lack of sound was how I knew it was pump related.

Last edited by reid-o; 08-21-2013 at 05:30 PM.
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Old 08-21-2013, 05:35 PM   #8
reid-o
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Also when I swapped out the pump, I couldn't remember if I changed the fuel filter when I installed the old walbro. I usually replace most parts when I remove something but I really could not remember. I just put the assembly back for now. That's next on my to do lost, but I'll probably run a straight line to remove the in tank filter and get one for the engine bay like a Golan or something.
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Old 08-21-2013, 06:24 PM   #9
dstroy
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Black with scratches

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Cool, I've got a sock on my pump and a 10 micron before my injectors. I'm pretty sure the FP relay is around $20 from Subaru and they're $8 from rockauto.
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