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Voltage Oscillation at WOT

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Hey guys,

I’m trying to figure out a problem I’ve had for quite some time. As soon as I put my foot down on the accelerator my voltage oscillates up and down very aggressively which causes my AFR to also oscillate. I added a few more grounds and checked my current ones, I got the alternator rebuilt but I have a feeling the diodes/regulator wasn’t replaced. I got the charge system tested with a snap on device which showed okay. But this only happens when I put my foot down and the system sees some load. I’ve attached a photo of a log that shows voltage. Does anyone have any other ideas that would cause this?

any help is greatly appreciated.


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It looks like you have a Link ECU, is it a plug-in or wire-in ecu? What model car?

Hey Adam, it’s a Evo 7 with a g4 PNP ecu. My battery tested out fine also I double checked my fuel pump wiring.


figured out the AYC pump is causing a huge draw every time it turns on and off causing a big oscillation in voltage. I’ll have to look further into the ayc pump now.

Bit of a long shot, but also check your ancilliary belt tension and condition - when the A/C engages it could be causing slight slippage and the alternator is slowing momentarily and dropping output voltage? After the initial slipping everything gets back to speed and the voltage is back to normal.

If you can hear a slight squeal as it engages, it'll be a confirmation for further investigation. Sometimes it's audible also from idle if you have the light, etc, on and the A/C operating to increase the total load on the belt, and you give the throttle a quick blip.

Found out it’s my AYC pump causing a serious draw every time it goes on and off. Thanks for throwing that out there!

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