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JDM Evo 7 AYC pump causing voltage drop/oscillation. Please Help!

783 Views 5 Replies 4 Participants Last post by  richyx
Hey guys,

I've been trying to figure this out for some time now, my AYC pump causes a large voltage oscillation when its pumping. (it always pumps after 50% throttle or so and turns on even in straight line) The voltage oscillation causes my dash lights to flicker/dim and my AFR goes up and down because the injectors areing seeing linear voltage at WOT. There have been a few others with the same problem on here but it never came to a conclusion. Another thing i noticed is when i have the engine off and ignition on and i step on the throttle, the AYC pump keeps pumping and never shuts off. Here is a thread with the same electrical problem.

Any help is greatly appreciated!

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The power circuit to the pump is quite simple and power is fed from Fusible Link 7 on the battery terminal block through a relay. This 100A fuse is (AFAIK) dedicated to the AYC pump. Also the pump ground is #10 which only serves the pump (and washer pump). So sounds like the pump is taking excessive current, not enough to blow fuse but enough to pull down battery voltage. I'm guessing you have boot battery with long cable which probably makes the effect of excess current worse on voltage to rest of system.

Could be a simple fault like a bad battery or corroded connector on battery - bet you've already looked at that though :).

After that for me it likely a pump fault. Doubly so because it's on in many cases when it shouldn't be which suggests it's not generating pressure. Could also be sensor issue but then that wouldn't cause excess currents.

If there is no pressure then I'd expect some AYC fault codes. Have you tried flashing out any codes?

I'd be tempted to disconnect the pump and feed it directly from the battery and see what heppens when its running, ie does the voltage drop. If it runs and voltage is steady then a possible cable loom issue somewhere?

Hope that helps
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