Guys,
Truck was starting hard a month ago, replaced GPR, all was fine up until a few days ago. Truck started starting hard again but this time I think it is the batteries. Gauge looks like 12v, voltmeter on the batteries says 12.6 on one and 12.3 on the other. When I hit the ignition she drops right down under 10v-9v-8v on the gauge but still fires after an extended crank. Running voltage looks great, 14v ish, so its being charged. Batteries are about 3 1/2 years old. Sound like a battery issue to you? Replace both at the same time, right?
Thanks

 

Time for Batts

Voltage should not drop below 10.5vdc while cranking

 

300mV is a lot of voltage drop between batteries, it's probably a bad battery, but try cleaning the battery terminals.

 

Yes you need to replace both batteries at the same time even if only one is bad. If you only replace one the older one will draw the new one down to it's level and they won't work like new batteries. Have the batteries load tested, most places will do this for free. I bought two new batteries this year from walmart. 60 bucks a peice and have a great warrenty, plus if one does go bad walmart is everywhere.

 

And then put some auxiliary cabling between the alternator and the battery. The slightest voltage drop between the alternator and the battery will cut the battery's life in half to 1/4.

 

Kwik, what do you mean by aux wiring from battey to alt? Just run a wire from the alt to the batt? What size? This is to keep the voltage the same threwout the entire charging system? What if you have two batteries and two alternators? Thanks i haven't heard this one

 

Using an additional wire between the alternator output, and + battery terminal is one approach, but the best approach is wiring the voltage regulator's "sense" to the positive battery terminal. This will compensate
for ANY wiring voltage drops, and a smaller wire can be used....

 

Dan,

I see you have added BOTH a (+) and a (-) cable from the alternator to the battery. Good point, the (-) leg of the circuit is just as important as the (+) side.

Also, in general, I've always wondered why vehicles have 100+ Amp alternators yet utilize a 8 or 10 Gauge wire to charge the battery. Never made any sense to me .

 

I've been doing this for nearly 20 years now with the VW's and Audi's that I work on every day. Where I live it's very crowded, urban, wet winter weather and you are doing good to get the engine up to speed at all. Cold, rainy weather = Heater, AC if on defrost, rear defogger, wipers, headlights on and the engine just loafing along in heavy traffic.
Also the wiring that VW installed on the cars was not the greatest and it would eat up to a full volt between the alternator and the battery. The alternator would be 14v at the post and 13.7v at the battery.
Turn on any accessories and it would drop to 12.5 - 13v at the battery with 14v showing at the alternator.
The older VW Rabbit and some of the early Golf/Jetta vehicles had aluminum for the conductor in the alternator wiring harness. DOH!
You can see with that scenario there is a VERY heavy load on the electrical system. I would get customer's towed in all the time with a dead and/or failed battery that's only a year old. The previous battery was not that old before they had it replaced. The solution was this wiring bridge to the battery. It completly cured the dead battery syndrome in more cars than I can remember, down to the last one. None of them ever came back with a dead battery after doing that repair.
So I just put them on anymore if the voltage is a little lower at the battery than it is at the output post of the alternator.

Yeah, that would work as well. Trouble is, I never figured out how to do that and this big wire helps carry any extra load very easily. No overheated wiring or fried posts.


PA_Ford_man I fully agree. One of my biggest pet peeves is inadequit wiring.
You can feel hot wiring when the car is just running.
Try it sometime, guys. Feel how warm the wiring is on the backside of your fuse panel on any brand of vehicle.

 

So i just upgrade my + wire from my alt to battery and my - wire from battery to ground? What size do you recomend, 4 gauge? Bob, you just run a wire from the + battery terminal to the alts sense wire? What size wire for that? Do you cut the wire going to the pcm when you do this or do you just solder this new wire from the batt to the existing wiring running to the alt? Thanks

 

Ponch, I've never modified one with an internal regulator. I would have to dig into one, to tell you how to do it.

 

Guess I'll just upgrade all the wiring to thicker wires then. Was thinking about doing that anyway but just have so many things to do to the truck and so many parts laying around that need to go on. Do you think 4 gauge wire is good enough. I am good friends with a local stereo shop owner so i can get wire for cheap. Thanks

 

Oops!
After looking more closely at Dan's picture, I was wrong about the (-) cable. I thought that is what it was, but now think it is a hose, not a cable. Although, it wouldn't "hurt" to have one .

Ponch: 4 Gauge is plenty. Get the "welding" type if possible. It has a higher strand count using thinner strands. Very flexible, like nylon rope!

 

It's not a hose, it's a 2g ground wire that bolts to one of the mounting bolts for the alternator and goes directly to the ground post on the battery.
The red wire is 6g, I would have preferred to use 4g, but was out at the time. It is simply attached to the output post on top of the existing factory wiring and is a parallel circuit. It's only function is to off load the charging load from the factory wire to the red wire. Electricity will take the easiest path and it will carry 60 amps or so. Now the factory wiring only has to run the truck and not also charge a dead battery back up again as well.
Both are made from welding cable and yes it's very flexible like nylon rope. Excellent stuff for making these cables
I didn't drive the truck in to work today, so I cannot take any more pictures until tomorrow. But if you all need some more detail, I'll be glad to take some more.
It's funny, I have one of those jobs here at the shop today: an old 1983 VW Rabbit diesel with a shot battery, dead alternator and needing a complete wiring rebuild.

 

Thanks for the help! Alright new batteries it is and a couple of cables too. I'll run to WalMart tomorrow for the batteries, anyone got any reason not to use a WalMart battery?