I know this isn't really drag racing related, but IMO the smartest hands-on guys frequent this section more and this problem surfaced after a new build so I'm sure I'm not the only one to experience it.

I cannot keep the voltage up in the car when it warms up at idle. At cold start its fine (14V), after it gets fully warmed up the voltage drops at idle pretty bad. I don't know how low it will go if I let it, but it kind of "pulses" lower and lower as you sit. I can get down to 11V at a typical red light. Once you rev it up it goes to 13V. I bought a 165 amp alternator for it, which failed after a few miles. They replaced it and this one seems to be working but the voltage drop is still happening. I've tried 2 different batteries (Odyssey dry cell and Optima yellow top), a smaller alternator pulley, and even stepped my idle up a bit. I've inspected all the cables, they look fine, although I haven't measured resistance across them yet. This problem surfaced after I had a stroker motor/blower setup installed. Other changes made at that time include larger injectors and a big magnafuel FP. I don't have much electrical draw on the system. 2 fans (one small 9", one 16"), FP, stock radio, ECM, thats about it.

I see no reason the voltage shouldn't stay up at idle? What is drawing so much? I had a problem with the FP, they rebuilt it and I actually tried a different smaller pump while it was being rebuilt and that didn't help the voltage so that rules the pump out. It does it with the fans off too. No lights, no A/C, no nothin'.

I'm going nuts here, the low voltage makes the amp draw higher on stuff and obviously slows down my FP and fans, which isn't good.

 

I had a problem when I relocated my battery.
This fixed the problem for me.
http://www.jegs.com/i/The%20''V''%20...65500/10002/-1

Is you guage cluster connected? It won't charge is it's not.

 

Gauge cluster is connected. It charges, I know that. I just don't understand why the voltage is so low? I've verified it with a scan tool too, not just the gauge on the dash.

 

Is the alt. belt slipping any at idle?

 

I don't see how it could? I even put on a new tensioner recently.

 

Sounds like resistance is building with heat. I would check all the simple stuff first. Battery terminals should not be a problem since you have changed the battery a time or two, but check them anyway for a good tight clean connection. Same for the alt terminal.

Has a battery ever leaked any acid? Maybe the stock delco? They are bad about it. Mine has actually got corrosion inside the cable from the battery to the alt from the factory delco. Yours may as well.

You may also have high resistance in the wire from the PCM/cluster to alt wire. I havent looked at a schematic but I know a tarnished pin in any of those connectors could cause an issue.

Maybe the wire got pinched some how in the motor swap, that could cause a resistance issue as well.

Check and make sure you have a good engine ground also. If you didn't it would probably screw up more than just the alt. but sometimes the simple things get over looked. Like powder coating on new parts like a alt relocation bracket or something like that.

A few things to look at, keep us posted.

 

I'm having the same issue, once the cars hot voltage drops. It's not as bad as your problem but i still need to fix it. I also changed batteries, and altenators. Next im got to replace the some of the cables and check grounds.

 

Battery in back TS6?

 

What's the alt output @ the stud, vs what you get @ the batt, when this happens?
Check all wire ends for integrity. A cold solder, or crimp, will cause this.

 

What size is the wire running from the battery up to the front of the car, and what size is the wire that runs back to the battery (assuming battery is relocated)

I used a HUGE *** welding cable to run up to the front, it's I think 00 guage, and the wire I ran from the alt to the back is a 4 guage.

Probably overkill, but with a 25% underdrive pulley I have no problems. Stock replacment alt, regular gold battery from autozone

 

My car is doing the same thing. To combat it I just purchased a 200amp alternator, and will be doing the "big 3 mod", which is replacing most of the big power/ground wires with 1/0 gauge wire.

 

For those not familar....Some good info, and a source for parts.
http://www.madelectrical.com/

 

My battery is still up front, stock cables. I've done a K member swap since the motor was installed and checked the wires and none were crimped. Obviously its realted to heat, but all alternators make less power once hot vs. cold. I would think if it was any sort of bad wire it wouldn't be temperature sensitive? I dunno, I might just put new cables on it. Whats a few more $$$ right?

 

I am having the same issues since moving the battery back. 0 cable for batery and true 4 gauge on the alt to the battery.

It would not bother me except the car won't start after three passes

 

Alright guys, its getting worse. My voltage is dropping even while driving. I noticed last night that everything is pulsing as well, headlights, FP, etc. I also noticed that when giving it more gas the voltage seems to drop slightly before it comes up. Its really pissing me off, I'm out of ideas and its getting worse. What should I do?

 

What does that thing do anyway? Just trick the alternator?

 

The way I understand it, it varies the voltage (through a manual adjustment) going to the alternator. I believe the unit steps up the voltage coming from the battery, then you adjust it down from there with the manual ****. Real easy to adjust and it's a cheap unit.

 

If none of the wires are crimped going to the ALT and battery that can do it. I'd crimp them all, and then solder them afterwards. That's a guarinteed good connection.

Do that first and see what that gets you. If that doesn't help, pull every non essential fuse you can, and see if that makes it go away. Just in case you have a short somewhere that you don't know about.


If that doesn't do anything, have the alternator load checked, and maybe get a new battery, maybe the battery/alt are just going bad.

 

I've used 3 different alternators and 2 different batteries, I'm gonna go ahead and rule those 2 items out.

Just went out and picked up another ground strap, never hurts to have more grounds.

 

Yes, make sure the battery is grounded good. I have a huge 0 guage wire running from my battery to one of the plates that my cage is welded onto, the motor has 2 large wires running from it to the chassis, and a motor plate bolted to it, and the chassis as well. I don't think that I could ground the motor much better.