One year ago, my original OEM alternator completely failed after nearly 10 years of hard use. I was three hours away from home in Ocean City, MD, and the only alternator I could get my hands on was a remanufactured AC Delco unit from Advance Auto Parts... sacrilegious I know, but better than being towed. A couple of SVTP and MACA brethren and I swapped it out, and it was able to sustain vital engine function while charging my battery. On my drive home, at steady highway speed, I monitored battery voltage on my AeroForce Interceptor, and I noticed the alternator’s voltage regulator doing a crappy job of regulating voltage. Battery voltage would briefly spike up to 15.7 volts and seconds later drop to as low as 13.3 volts, but rarely would it settle around 14.5 volts which is what I would expect from a new alternator. Within one week of being home and uncomfortable with poor voltage regulation, I dropped by my local Ford dealer and ordered a new OEM alternator. I removed the AC Delco unit and installed the new remanufactured OEM alternator. I actively monitored battery voltage, and everything appeared normal again. In the Fall, I decided that it would be a good idea to capture a good datalog to see how well everything was performing. To my surprise, battery voltage dropped under WOT and my fuel system started to lean out early. I never got a battery light or “check charging system” warning. This situation was very repeatable, so I sent a datalog to JDM and they confirmed that low voltage at the fuel pumps was most likely causing the lean situation since my previous Dyno tuning logs showed steady fuel delivery up to 6600 rpm, where my rpm limiter was set. On JDM’s recommendation, I installed a PA Performance 130A alternator with 10% underdrive pulley and premium wiring kit. Alternator voltage regulation was tight once again at about 14.7 volts from idle to redline, but it was unsafe to go WOT due to cold temps and poor traction. Last week, outside air temps were finally high enough to have full traction for a third gear pull to datalog. Both datalog graphics below show battery voltage, rpm, and AFR. With the new remanufactured OEM alternator, you can see the alternator stop charging and AFR starts to lean out at about 5800 rpm, and I lift at 6300rpm. My AFR got uncomfortably high but not critically high at that rpm; I run a slightly rich AFR to keep my OEM cats alive at my power level. Left unchecked, this could have turned out badly. With the new PA Performance alternator, AFR stays constant through 6100 rpm, and I confirmed it with another pull to 6200 rpm. My advice to anyone demanding maximum performance from their vehicle is to datalog critical parameters at least once a year to make sure everything is functioning properly. I usually capture a datalog after my Spring maintenance is complete and I have filled up with a fresh tank of 93 octane. If all looks good, I let her eat!
