Alternator / built in regulator going out?

[DC_MPA]

My mechanical friends - I own a 2002 gmc envoy that was grandmas car before it was mine. She put 54,000 miles on it and I have put 27,000 totaling 81,000 miles. Factory everything and loaded everything. My battery started giving me a sluggish start in September, I had it checked and it was the battery going dead (and it was time for that to happen). I replaced it with a higher cold cranking amp battery from O'Reilly's auto. Since then and gradually getting worse comes my lights. All internal and external lights fluctuate day or night. By fluctuate I mean at a 100% full glow normal they bounce between 80-100% at a flutter speed. I've cleaned the throttle body to make it like new, new bolts on the side terminal battery, cleaned the battery terminals to shine condition. I've had the alternator, diode, volt regulator and starter checked at 3 different parts stores (I've noticed they all use the same handheld device to check) and everything checks perfectly fine. Only once did a test show us that at idle the amps shift from 45 to 65 in a matter of 2-3 minutes between tests. Lastly, my volt guage on my dash bounces from 14.5 to 16.5 and dances in that zone with the rare dip below 14 to around 13 and the it immediately jumps back in the 14.5-16.5 window.

Could it be the alternator even though it is testing fine?

as always I can't thank my fellow B&B friends enough for all the advice and help.

 

[BBrad]

Sounds like you might have a bad ground connection somewhere. Check the negative battery cable where it bolts to the engine block, as well as the ground strap from the engine to the frame. Pull the alternator and clean the mount points.

Also, make certain that you aren't getting any belt slippage - your serpentine belt could be glazed or your belt tensioner (idler) pulley may be allowing slippage.

Amperage is only a measurement of current being drawn at that particular time. Voltage drop is a better indicator of connection issues.

 

[DC_MPA]

Thanks for the feedback Brad! The first ground was right off the battery and I took it off, made it shine again and bolted it back. The second is the ground splice where apparently a bunch of grounds come together into one bolted location. It's a pain as I have to take off the entire center console to expose it but at the same time it looks like it should be a 30-45 min job. I'm off to do that now.

 

[DC_MPA]

Okie dokie. Got to the master ground splice, made the bolt, washer, and plate and frame base shine again. It seems a lot better but still there. My volt gauge definitely is more stable but still wiggles slightly between 14.5-15.5 which is in the normal range but my lights still flicker internal and external.

 

[BBrad]

Did you pull the alternator and clean the mounting points/pivot? The outer case of the alternator is part of the ground circuit. If it is not getting a good ground connection between the case and the bracket/engine block, all bets are off!

How about the ground connection between the headlight socket and the body/frame? Those can make the headlights dim if they aren't 100%.

 

[DC_MPA]

That ground in the front is also checked and thoroughly cleaned. I've never done an alternator before so I'm going to get a buddy of mine to oversee me do it with a beer honesty at 10yrs old I'm mulling of throwing in a new Remy alternator with a new gator back serpentine belt just for routine maintenance at 80k miles and 10 years of service.

Any thoughts on the Remy brand alternators Brad?

 

[DC_MPA]

Brand new alternator, checked the grounds. Everything is either shining like new or is new. Any other suggestions? I surely thought it would be the volt regulator in the alternator.

 

[BBrad]

Are you 100% sure of the grounds? Especially between body, frame, and engine block? There may be more than one . . .

In my experience, alternators either work or they don't. Voltages running up and down are not caused by electronic regulators, but rather by changes in load or the ability of the alternator, battery, and wiring to respond to that load. Bad ground circuits increase amperage loads which causes voltage drop across the load.

Try turning off all lights and accessory items, and placing a digital volt meter across the battery terminals. With the engine running, you should see somewhere around 14.5 to 15 volts, and it should remain fairly steady. Start adding load, one accessory at a time, until you see fluctuations in voltage at the battery. That may help isolate what circuit is drawing down the voltage. Then look for poor connections (both ground and hot) within that circuit.

 

[DC_MPA]

I can't say I've checked them all but so far I've found 8 different grounds that I've taken off and cleaned. Advance auto did a bunch of tests today at different RPM and loads as you suggested earlier today. As the volt meter on the dash danced between 14-16 and the lights all flickered, every test on the alternator, regulator, diode, battery, and starter all came back great. The variance on all of our tests was within a few tenths and all tests stayed within 14.5 and 15 volts. With adding one load choice at a time until everything was running (lights, fan, radio, etc) nothing caused a shift. The light and gauge flicker was even with everything off.

What's weird is this started the next day after I put in a new battery in September.

 

[BBrad]

What's weird is this started the next day after I put in a new battery in September.

Whoa . . . that's a horse of a different color!!

The battery cable assemblies have multiple wires that connect each terminal to more than one point. For example, the positive cable connects to the starter solenoid and alternator output, as well as to the main fuse block, lights, etc. One of the smaller cables could have broken wires in them, or internal corrosion due to moisture getting underneath the insulating sheath. When you disconnected the old battery (and probably cleaned the terminals) the damage could have gotten worse, making the problem show up the next day.

On the ground side, the negative cable assembly generally connects to the engine block and body/frame ground points. Again, suspect the smaller-diameter frame ground wire.

You've certainly eliminated the big things as being the cause . . . maybe new battery cable assemblies is the answer?

 

[DC_MPA]

Wizard of Oz quote - love it

funny you mention that, just today while putting in a new fuel filter (I'm one of those people that change it annually) and I thought of the battery cables.

Just looking at the interweb connections (as you described above perfectly) seems like a nightmare. More so than putting in the alternator, serpentine belt and throttle body (all of which I've done for the first time on my life this past week).