I have an 05 Crown Victoria and when I blip the throttle the voltage will jump to 15+ volts for a brief second, I put in a brand new alternator and it still does it, wondering what the issue could be. It charges at 14.7 and will get as high as 16v despite having the old or new alternator installed. Brand new duralast agm as well. Could this be a pcm issue or a short from the alt pigtail to the pcm?
start with all six steps of this test… https://i.imgur.com/SnzhDh0.jpg
then be sure that during test 5 in the underhood fuse block that you check the voltage drop on fuse F1.6. this fuse supplies power on the Orange/light blue stripe wire to the regulator connector cavity A
please spend the time with test 5 to do all the fuses you can get to in the underhood fuse block
this is only the beginning of your diagnosis…
you are probably going to need an scan tool to see what the computer voltage looks like in the scan tool live data stream… see if that surges also. or if its slow to respond.
please don’t test any other wires plugged into the voltage regulator…
you may want to examine the PCM connector for signs of corrosion… i have run into that on other crown victorias…
the alternator output is controlled by the PCM… so you could have some electrical connection issues…
Sorry for the late reply just got to diagnosing today, most of the fuses read .014V but I did notice they will jump from .014v to .017v whenever the compressor engages?
That tends to indicate that there’s a power supply issue between the battery and the fuse box so you might want to see if you can isolate which connection it is by using the voltage drop test across the joints so you’re going to go from like the battery terminal to the wire that goes to the fuse box about an inch from The Ring terminal and then at the other end this inverse of that so the wire strands to the ring terminal and in the ring terminal to the underhood fuse box something something’s a little iffy there it might not be much it might be just the current but you need to prove that if the overall voltage drop that’s changing still not very much
