So I first noticed this problem a few weeks ago when I had to drive my truck to school because I was fixing something on my daily driver. On the freeway I noticed that my analog voltmeter was reading around 12 volts and was slowly going down. I initially thought that my alternator went bad and eventually the voltmeter was reading 9 volts and I was sure the truck would shut off at any time. My speakers (aftermarket system) started crackling so I turned off the deck, and the voltmeter shot back up to 14 volts. Unfortunately I didn't have a DMM on me at the time, so I wasn't able to check the voltage. I drove home fine that night and thought it was just an oddity.
So this week I pulled my truck into the garage to charge my batteries up for a car show / sound competition this weekend. The charger was showing full capacity after the first day, and I left it on to keep a float charge until I pulled it out to wash it this morning. Got ready to go to the show and left my house, noticing that the voltmeter was reading very low again. I checked the voltage before leaving my house with the truck running and it was at 14.1 volts both at the front battery, and at the amp terminals in the back. So I left, and within 5 minutes the voltmeter dropped to 9 volts like it had before, so I pulled into a neighborhood and parked. The speakers were crackling, but when I went to check the voltage at the front battery it was at 15.5 volts.
I turned off the truck thinking that the voltage might keep climbing and wanting to prevent any damage from high voltage spikes. Let it rest for a few minutes, but then when I tried to start it back up it won't even crank. When I turn the key it would shut off all the lights on the dash, and then a few seconds later I heard a buzz noise and my seat moved back to the "key out" position. So I had it towed home, and now I don't even know where to start. The resting voltage is around 12.5 (low, the batteries aren't in the best shape) but there should be more than enough juice to crank the truck with 280 AH of capacity.
The only thing I can think of is that the PCM is misreading the voltage that the alternator is charging at. This might explain why the alternator was charging at 15.5, the PCM was sending a signal saying that it wasn't charging high enough and it ramped up the regulator. I'm not sure why the speakers would crackle with the amps receiving the correct voltage, unless the RCA's were putting out wacky voltage due to the deck being wired to ignition or something? Speaking of which I've read that the ignition switch is known to go bad on our trucks, do these seem like symptoms of a bad ignition switch?
I'm planning on swapping in my stock PCM tomorrow, I currently have one with a tune from PCMofNC. I literally don't know what else to do since I know that the voltage is where it should be, just the PCM is not reading it right.
So this week I pulled my truck into the garage to charge my batteries up for a car show / sound competition this weekend. The charger was showing full capacity after the first day, and I left it on to keep a float charge until I pulled it out to wash it this morning. Got ready to go to the show and left my house, noticing that the voltmeter was reading very low again. I checked the voltage before leaving my house with the truck running and it was at 14.1 volts both at the front battery, and at the amp terminals in the back. So I left, and within 5 minutes the voltmeter dropped to 9 volts like it had before, so I pulled into a neighborhood and parked. The speakers were crackling, but when I went to check the voltage at the front battery it was at 15.5 volts.
I turned off the truck thinking that the voltage might keep climbing and wanting to prevent any damage from high voltage spikes. Let it rest for a few minutes, but then when I tried to start it back up it won't even crank. When I turn the key it would shut off all the lights on the dash, and then a few seconds later I heard a buzz noise and my seat moved back to the "key out" position. So I had it towed home, and now I don't even know where to start. The resting voltage is around 12.5 (low, the batteries aren't in the best shape) but there should be more than enough juice to crank the truck with 280 AH of capacity.
The only thing I can think of is that the PCM is misreading the voltage that the alternator is charging at. This might explain why the alternator was charging at 15.5, the PCM was sending a signal saying that it wasn't charging high enough and it ramped up the regulator. I'm not sure why the speakers would crackle with the amps receiving the correct voltage, unless the RCA's were putting out wacky voltage due to the deck being wired to ignition or something? Speaking of which I've read that the ignition switch is known to go bad on our trucks, do these seem like symptoms of a bad ignition switch?
I'm planning on swapping in my stock PCM tomorrow, I currently have one with a tune from PCMofNC. I literally don't know what else to do since I know that the voltage is where it should be, just the PCM is not reading it right.
