Charging System Question

slazzara · 07:35 AM

Need help guys (or girls)...I have a '74 914 2.0 and I'm having an issue with my charging system. I can charge my battery to 100% but when I test volts with the engine running, I can only get 12.9-13.1. I don't think my alternator is bad. The light isn't on or anything. Wouldn't a bad regulator mean a higher reading on the voltmeter? After charging the battery to 100%, I drove it for about an hour with the lights on last night. By the time I got back home, battery was dead.

Any help is appreciated

Dave at Pelican Parts · Dave at Pelican Parts's Garage

It should take more than an hour of driving with the lights on to kill a fully-charged battery. Even when the alternator isn't working. I think you may have some other problem--possibly the battery isn't holding much of a charge?

How are you measuring the charging system voltage? If it's on the voltmeter in the center console, low and inconsistent readings are very common. You'll notice it reacts significantly when you hit the brakes, or turn the headlights on. The voltage across the battery terminals should not react nearly that much.

--DD

slazzara · 11-29-2013, 02:37 PM

I measured with a voltmeter across the terminals. Maybe it's a bad battery? But then why can I charge it to 100%

Dave at Pelican Parts · Dave at Pelican Parts's Garage

How do you know it's 100% charged? That measurement might be in error.

You can take the battery to your FLAPS (Friendly Local Auto Parts Store) and have it tested. They can tell you if it is actually holding a charge or not.

--DD

slazzara · 11-29-2013, 04:19 PM

I have a charger that displays the total charge but you are right. I'll never know if it's holding the charge. I'll need to get it tested for that. Shouldn't the reading on the voltmeter be 13.6 or so with the car running though?

Dave at Pelican Parts · Dave at Pelican Parts's Garage

In newer cars, we see up to 14.4V, depending on the load on the system.

I have yet to see a 914 that charges consistently over 14V, though. Mine, with an adjustable voltage regulator, goes up to 14V occasionally, but mostly stays in the 13s. As long as it's over 12.6V, it is charging at least a little bit.

--DD

slazzara · 11-30-2013, 12:01 PM

Well..something's not right. I took the battery down to get tested and it tested fine. I guess I'll try switching out the regulator and go from there. Thanks for your help

John Rogers · 11-30-2013, 01:21 PM

I would look at several things: the battery, the cables/ends, the alternator and regulator/circuit board in the engine compartment. You said the batter tested fine at a dealer so I would suggest measuring the resistance of the cables, especially if they are more than a few years old. How good are the end connectors? Make sure they are in spec. Next is the alternator and regulator and generally if one goes bad, the other gets over worked and will start to fail too.

T77911S · 12-02-2013, 02:56 PM

the cables themselves dont generally go bad. the problem is connections. even how the cables connect to the batter clamps or the crimped ends that either attach to the body or the starter.

with starting and charging issues always start with a tested good battery. then clean all the major connections, both positive and grounds. the battery to the body, the tranny to the body.

battery voltage is 12.6volts. so the battery needs a higher voltage than that to charge. 13-14v is ideal. a good test in the car is like you did, with the engine running, turn on as much stuff to put a load on the system and check the voltage AT the battery.

if you dont have the correct voltage the best thing to do is take it to some place like advance that will check the charging system for FREE. otherwise it is just a crap shoot as to the alt or the regulator.
dont waste your money until you know what is wrong. just make sure all your wiring connections are clean good.

slazzara · 12-06-2013, 10:15 AM

Hey guys...Thanks for the help. I got a new regulator and I'm now reading 13.5-13.7. So it looks like that did the trick. I'm going to possibly order a new ground strap as well and I've cleaned the connections. The new regulator though doesn't line up well with the existing screw holes. How important is it that the regulator is screwed in? It looks pretty secure as is.