Voltage problem

[Red94Chev]

Ever since I've installed my new motor, I have a voltage problem where the voltmeter on the dash reads 9-11 volts instead of 13-14 volts. It is an intermittent problem and I will often see the voltmeter jump up suddenly and stay at 14+ volts for awhile. When at 9 or 10 volts, I have problems with turning over the engine and I get the occasional backfire. One time, I've had the engine shut off entirely while driving and then the electronic transmission stuck in overdrive when restarted. All voltage-related and the problems disappeared with adequate voltage.

I'm pretty sure the problem is in the engine bay and likely a bad ground connection somewhere or a hot wire grounding out. A new alternator and battery were tried and that does not seem to be the problem. The only thing I've noticed is turning the headlights on and off sometimes improves the voltage. Using the signal lights sometimes drops the voltage suddenly, but it has only done this a few times. I've pulled the fuses from the fuse panel to see if I could isolate a circuit, including the headlights and signal lights, to see if that was causing the problem. No luck. That's about as far as I've taken it so far.

Just wondering if anyone else has had this problem before. I took it back to the mechanic who installed the engine twice, but he could not find any problems and said the charging system was working perfectly. Finding electrical problems is like finding a needle in a haystack. Any bright ideas?

[Copper93]

It does sound like a grounding problem. Check the block to frame ground and the battery to block ground. You might also want to look at doing the "big three" setup. You run bigger cables from the alt to the battery, the battery to block and block to frame. Search the forum for "Big Three" and you'll see what I'm talking about. Good luck, hunting down a voltage problem is a pain in the rear.

[305ho]

When you put in the motor did you install the groud straps from the block to the frame and fire wall?

[Red94Chev]

Yeah, ground strap is there at the back of the engine connected to the firewall. The interesting thing is it seems to do this during hot weather mostly.

[Yukon04]

Mine was doing the same thing this summer, mostly when it was hot out. The drive in to work it was fine and the drive home in the afternoon it would act up. I did a load test on the battery, battery was dead. It was fine for a couple days after I put in a new battery and then started acting up again. I took it up north last week for a moose hunt and it never moved off 14 volts on the drive up. It hasn't been lower than 14 since then. I was thinking the grounds but I never had a chance to check them though.

[Red94Chev]

Yeah, I'll try the big three, but there's probably something else going on too I'd suspect. Like I said, no problems before I changed engines. Pretty sure the problem is in the engine bay somewhere.

Originally Posted by Copper93

It does sound like a grounding problem. Check the block to frame ground and the battery to block ground. You might also want to look at doing the "big three" setup. You run bigger cables from the alt to the battery, the battery to block and block to frame. Search the forum for "Big Three" and you'll see what I'm talking about. Good luck, hunting down a voltage problem is a pain in the rear.

[dave89iroc]

clean or run a new ground from the battery to the body, I fixed a 95 truck at work yesterday with this exact problem

[Red94Chev]

Thanks for the tip. I'll give it a try.

[Red94Chev]

Just an update in case someone else has a similar problem. I ran new cables (positive and negative) from the battery and it fixed the problem. There was quite a bit of corrosion at the junction box on the firewall as well (under the plastic shroud) and I cleaned it up just to be sure. In retrospect, I probably should have tried this first as this might have been the problem all along. Glad is it working properly now though.