Voltage Regulator?

Dangerous Doug · #1 (**permalink**) 11-25-2009, 02:28 PM

My Cobra died twice yesterday, and once today while sitting at a stop light and then while creeping over a speed bump. It dies, and there is no power so I flip the switch on the remote battery cut-off, and then it fires right back up.

Odd.

Today, I'm at a stop light and I notice that I cannot see the reflection of my headlights on the back of the car in front of me. I blip the throttle and the headlights brighten up.

Really odd.

At first I thought I might be having a problem with the remote battery cut-off solenoid, but when I saw the headlights fluctuate in brightness just by blipping the throttle (spinning the alternator up), it now seems my voltage regulator is the culprit.

The amp gauge seems to be reading correctly (i.e. it's charging) so I don't think it's the alternator (I just had one go out on my Jeep---which was a total pain in the ass to replace, but that's a different story....)

Anyone see anything like this before?

DD

Ron61 · #2 (**permalink**) 11-25-2009, 02:37 PM

Doug,

Before I completely relied on the amp gage I would measure the battery voltage with the car running. That is why I used a voltage gage instead of an amp gage in my car. And it could be the regulator or a bad ground.

Ron

Gunner · #3 (**permalink**) 11-25-2009, 02:38 PM

Repeat this mantra about 427 times... oh, sorry, 289 times in your case: "Ammeters are useless window-dressing in modern cars." By modern, I mean any car with an alternator. The generator days were a little different, but with modern alternators and voltage regulators (and I'd bet you have a modern VR, maybe hiding under an era-style case), ammeters are somewhere between chrome knob and idiot light in usefulness.

If you don't want to swap it out for a voltmeter, attach a voltmeter to your electrical system as a test instrument. You should see 11.8-12.2 volts with the engine off, no lower than about 9 volts (maybe 8, with an older battery and big engine) during cranking, and a fairly steady 13.5-14 volts while the engine is running, no matter the RPM or electrical load. Anything else, you've got a problem that's easy to diagnose. Post some numbers if you can.

Ronbo · #4 (**permalink**) 11-25-2009, 02:55 PM

Quote:

Originally Posted by Gunner

Repeat this mantra about 427 times... oh, sorry, 289 times in your case: "Ammeters are useless window-dressing in modern cars." By modern, I mean any car with an alternator. The generator days were a little different, but with modern alternators and voltage regulators (and I'd bet you have a modern VR, maybe hiding under an era-style case), ammeters are somewhere between chrome knob and idiot light in usefulness.

If you don't want to swap it out for a voltmeter, attach a voltmeter to your electrical system as a test instrument. You should see 11.8-12.2 volts with the engine off, no lower than about 9 volts (maybe 8, with an older battery and big engine) during cranking, and a fairly steady 13.5-14 volts while the engine is running, no matter the RPM or electrical load. Anything else, you've got a problem that's easy to diagnose. Post some numbers if you can.

Untrue, amp meters, like volt meters, leave you guessing on some things. A voltmeter CANNOT tell you how much current the alternator (or generator) is producing. Ideally it's best to have both.

Pop a diode in your alternator and you'll find out how valuable an amp meter is...

BTW: this could very well be what's wrong here...

Gunner · #5 (**permalink**) 11-25-2009, 05:46 PM

Quote:

Originally Posted by Ronbo

Untrue, amp meters, like volt meters, leave you guessing on some things. A voltmeter CANNOT tell you how much current the alternator (or generator) is producing. Ideally it's best to have both.

How much current the alternator is producing is largely irrelevant. If it's not producing enough net power, the voltage will show it.

I'll stand on what I said. It might be useful to have temp gauges for your transmission and differential, too, but most drivers wouldn't find them worth the dash space. The itty bit an ammeter tells you vs the complete story a voltmeter shows isn't, IMVHO, worth the dash space.

Name a problem with an automotive electrical system that a voltmeter, alone, wouldn't diagnose. Go ahead and list everything an ammeter diagnoses, while you're at it - it won't take any more space.

Ronbo · #6 (**permalink**) 11-25-2009, 02:46 PM

Possibly, I'm guessing the Ammeter shows a discharge at idle?

Easiest thing first, is the belt tight? Then have the Alternator tested at the parts store. If the Alternator tests OK, get a replacement regulator since your already at the parts store...

A spare regulator can be handy since it's a part a lot of stores won't have in stock anyway.

Dangerous Doug · #7 (**permalink**) 11-25-2009, 03:12 PM

I'll stop by my local shop for an in-circuit alterator test today.

I'm thinking regulator, based on the fluctuation I see in the headlight brightness.

DD

Ronbo · #8 (**permalink**) 11-25-2009, 04:01 PM

Quote:

Originally Posted by Dangerous Doug

I'll stop by my local shop for an in-circuit alterator test today.

I'm thinking regulator, based on the fluctuation I see in the headlight brightness.

DD

I won't rule out the regulator, but your description of reving the motor and the power comes back sounds more like the alternator has reduced output. The regulator can only push what the alternator produces.

Gunner · #9 (**permalink**) 11-25-2009, 05:56 PM

Quote:

Originally Posted by Dangerous Doug

I'm thinking regulator, based on the fluctuation I see in the headlight brightness.

Unlikely. Modern VRs don't tend to "partly fail" - they either quit permitting battery charging (which is the more fail-safe option) so that the power gradually runs down, or they never stop charging the battery, which cooks it. A variation when you rev the engine etc. is more indicative of reduced battery charge, which can be caused by many things.

A loose alternator belt is one common cause. A failing battery is another. Since you do get response at revs, it's likely not the alternator itself. I'd bet on a loose belt, a bad battery, a bad connection somewhere preventing battery charging, or - very last option - a bad regulator.

Dangerous Doug · #10 (**permalink**) 11-25-2009, 06:32 PM

Replaced the regulator today, and the headlights are consistently bright (no variation).

I had a guy run a tester at the local parts shop, and the battery and alternator both tested good, but the voltage seemed to wander a bit.

The old regulator was the standard issue Ford box. I replaced it with a higher quality regulator. When I replaced the old one, it was really hot to the touch---but that may have been just the proximity to the headers (about a foot away).

I thought I was done, but on my "test drive" (i.e. excuse to go out for a drive) I found on occasion that if I made an aggressive stop, the engine would die. I'll have to search for threads on this one.

DD

Blas · #11 (**permalink**) 11-25-2009, 06:34 PM

Check your grounds.
Check your ignition box connections.
You running a MSD with a mag pickup?

Dangerous Doug · #12 (**permalink**) 11-25-2009, 07:48 PM

I have an MSD ready-to-run distributor but no box.

DD

Blas · #13 (**permalink**) 11-25-2009, 08:52 PM

Agressive stops and stalling can also be related to carb floats...Any movement on the AMP meter when the car stalls? Battery water levels ok?

Joe Wicked · #14 (**permalink**) 11-30-2009, 10:19 AM

Keep in mind that just because it works now, does not mean that was the root of the problem. I have seen many bad components cause a load on the VR that will cause it to fail. If the new VR fails in a short amount of time of use, then something is causing it to fail and that is the true root of the problem.