Voltage drop at speed

[idM1028]

It seems I've been having this issue for a while, it wasn't until recently and the purchase of a voltmeter that I've noticed its an issue. Long story short, no matter what I do, GEN1 doesn't seem to want to charge the front battery at speed. At idle, the truck will usually put out sufficient voltage (voltmeter in the green or borderline green/yellow) but at speed the voltage drops. The problem is most noticeable driving down the highway at night with the headlights on, but I tested it today with the truck parked with no lights at all on and still saw a voltage drop on the front battery when I revved the engine. Is this normal? And if not what could be causing it? Today I replaced out GEN1 with the Autozone Caddy alternator (DL7157) since the idiot light was coming on at speed (still figuring out the electrical system, but this should mean my exciter wire/circuit is working correct?) Sure enough, new alternator and the light went out. I also made sure that all my belts were good and tight when I put it in. My front battery could probably get put on a charger, since its a bit under 12V. Honestly, I might go swap it out next time I'm at Pepboys since its a Yellowtop and should still be under warranty. I also cleaned up all the electrical contacts I could the other day. While doing this I kept an eye out for shorts and frayed wires and was unable to find anything.

 

[tbearatkin]

Make sure your GP relay is not energizing. Mine was doing that even after warming up. Could see the volt meter dropping down and back up when it de-energized then back down when it kicked in again. The clicking is very distinct.

 

[idM1028]

Make sure your GP relay is not energizing. Mine was doing that even after warming up. Could see the volt meter dropping down and back up when it de-energized then back down when it kicked in again. The clicking is very distinct.

I've been having this issue too and I know what you're talking about. The GP relay seems to be going back and forth a bit more than it should/used to. I've got a new GP relay coming in this week since I cracked the housing trying to get the contacts off but once the truck gets running it stops. I also noticed that the GEN1 light is STILL coming on at speed. Granted, it only does it at the very top end and its not bright as before, but its still doing it.

 

[idM1028]

OK, I just found the troubleshooting instructions in the CUCV FAQ thread. With key off, everything's looking fine. Like I said, front battery's low, but I was getting 11.7 volts on the red wire for the alt and the red wire on the plug. With key on, the voltage dropped almost a full volt to 10.9 volts! Exciter wire was a bit lower at 10.7 volts.

 

[tbearatkin]

I've been having this issue too and I know what you're talking about. The GP relay seems to be going back and forth a bit more than it should/used to. I've got a new GP relay coming in this week since I cracked the housing trying to get the contacts off but once the truck gets running it stops. I also noticed that the GEN1 light is STILL coming on at speed. Granted, it only does it at the very top end and its not bright as before, but its still doing it.

If you are still having this problem after replacement your controller card is probably bad or have dirty contact points. To solve this temporary take take the pink wire off the top of your GP relay after it warms up. Relay cannot energize. OR just do the bypass of the system and install a push-button glow-plug doghead style.