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Thread: Fuel pump issues

  1. #1
    Junior Member
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    Sep 2012
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    Baltimore, MD
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    Fuel pump issues

    Hey, I was wondering if someone could help me with my fuel pump issues. To give a little history of my current progress, I am almost done with my 818s build in Gaithersburg, MD. The car was running last year but I build progress slowed down to a crawl when I moved to baltimore and did not have a garage to store my car so I kept the car at my parent's house. When I moved it, I was able to drive the car around and into the trailer. Now that I am just about ready to go get it inspected, the car started having problems starting and idling. I found out my fuel pump was stopped working. I have an external fuel gauge so I could verify that there was 0 pressure.

    Normally when I turned the car from off to acc, I would hear my fuel pump turn on and prime the system but now it does not do that. I replace my stock fuel pump with an AEM aftermarket fuel pump in case that it was a bad pump because while it was in storage or in case it was just old but that did not help. I checked the voltage at the connector to the fuel pump and it was only producing 10 volts which I am guessing is the problem but I am not 100% sure because I think the fuel pump module may change the duty cycle of the pump from 0%, 33%, 66%, and 100% instead of changing the voltage and it may just be that my multimeter just took an average. To test this, I disconnected the fuel pump module and shorted pins 1-4 and 3-6 so the fuel pump relay (that was providing 12volts) controlled the fuel pump directly. After I did that and turned on the car, I could hear fuel pump turn on and the external fuel pressure gauge showed I had pressure. I was hoping I had a bad fuel pump module so I bought I used one online and replace my old one but unfortunately that did not fix the problem. The only thing left I can think of is if the ECU is not giving the correct signal to the fuel pump module.

    Any suggestions on what could be the cause of my problem? not sure if it is a bad ground or something but I would not know which ground to check. Or should I bypass my fuel pump module and just have the fuel pump run constantly when I turn it on ACC?

  2. #2
    Senior Member STiPWRD's Avatar
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    Depending on what sort of AEM fuel pump you got and how much more it flows vs. stock, turning it on directly to 12V will likely overwhelm your stock fuel pressure regulator and the engine may run a lot more rich. But it can be done if you get a better aftermarket fuel pressure regulator. One way to check if the fuel controller is getting the right signal from the ECU is to measure voltage on the ECU demand wire (color VW, pin 8) on the fuel controller. This should be a 0-5V signal.

  3. #3
    Junior Member
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    The AEM fuel pump says it is supposed to be 320 lph at 43psi. I am not sure what stock was. Fortunately, I have also have an aeromotive fuel pressure regulator and upgraded fuel rails. Do you think it would be easier to take out the fuel pump module? I leaning towards doing this vs continuing to diagnose and find the root cause if it is safe to do it.

  4. #4
    Senior Member STiPWRD's Avatar
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    If you have the aeromotive FPR, you should be able to run the pump directly off 12V power and bypass the fuel controller. Check the max current draw of your AEM pump and make sure the wire gauge you select to run the pump is sufficient. I'd suggest running the pump off a high current relay switched by ACC power (don't forget a fuse). Try running the engine and measuring your air fuel ratio and monitor your fuel pressure.

    One issue with running the pump without load modulation is that you'll likely need to retune the ECU. If you want to retain a fuel controller and not have as much retuning, here is an aftermarket one that works like stock but can handle a higher current fuel pump.

    https://www.dccdpro.com/product/fuelpro/

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