[MWright936]

I have a 2005 Silverado with the 5.3 and about 182k miles. Within the last month, I started noticing every light on the truck will start pulsing/flickering. This seems to mostly happen when I’m at an idle, and it will randomly idle rough. That’s when the lights will pulse. If I rev the engine, the flicker will stop. Although, I also have noticed it while driving when at low RPM’s. Every light on the truck will do it...headlights, tail lights, dash lights, dome lights...you get the picture.

I thought it might be alternator or battery related. I also noticed a leaking brake booster check valve. I had my battery and alternator tested. The alternator tested good, but the battery tested bad. I bought a new battery and replaced the check valve. None of this made any difference.

I’ve done some Googling, and a common answer is a loose voltage regulator. I don’t think this is my issue because it doesn’t coincide with driving over bumps or anything, just rough, low idle. Everything else seems to be working perfectly, and there is no check engine light on.

Does anybody have any thoughts?? I’m at a loss. Not sure where to look first.

Thanks!

 

[Zach Smith]

What are your rps at rough low idle?

 

[MWright936]

What are your rps at rough low idle?

I paid more attention to RPMs this morning. When I first crank the truck, they’re right at 1000. After a minute or less, they start to slowly drop. When they hit about 700, the lights start to pulse slightly. I sat there for a bit, and it hung there, then I went to work. After the engine is warm (and I’m in park), the idle will drop to about 500-600. That’s when the lights more noticeably pulse/flicker and the idle is a bit rough to where sometimes it shakes the truck a little, but that rough idle tends to come and go.

Any thoughts?

 

[xPosTech]

Matt what do you mean by "loose" voltage regulator? Regarding voltage regulators loose can mean a wide regulation target voltage. Something like -3V and +3V might be considered loose where -.5V and +.5V might be considered "tight". The other obvious meaning is that the mounting screws inside the alternator are loose and not properly grounding the body of the regulator.

In the first case vibration will have no effect on the regulation. In the second case vibration may or may not affect the regulation.

Things you can do are to clean the battery cable connectors and posts with a wire brush to insure good connections, check the cables from one end to the other, especially the grounds and the cable ends at the alternator and starter. Clean the MAF and the throttle body with MAF cleaner and TB cleaner. After cleaning the MAF & TB, disconnect the negative battery cable for a few minutes and reconnect. This will zero the learned idle characteristics of the engine.

Ted

 

[jasons99hoe]

i had a voltage regulator fail. seem like what it is to me but i aint an expert. i didnt think they were intermittent when they fail. they either work or dont.

 

[Zach Smith]

Your rpms are in check, was making sure you didn't have some other drivability issue mimicking a voltage/amperage issue. Check output, directly at alt...check sense wire directly at alt...what to we have there? What do we have at batt? What do we have at alt fuse? What do we have on headlight pigtails... Lights plugged in, lights disconnected? Any voltage where ground should be...high resistance? I know you already checked once...just covering bases...

 

[Zach Smith]

It is perfectly likely that the alt that is new is bad also...but let's chase a few things first...or you can warranty alt and see if you want...sounds like you have been through that already

 

[jasons99hoe]

It is perfectly likely that the alt that is new is bad also...but let's chase a few things first...or you can warranty alt and see if you want...sounds like you have been through that already

dont wanna step on toes but he tested alternator not replaced it. but i ilke your suggestion of checking different areas instead of throwing money at it. like you said it could be something in wire

 

[xPosTech]

Our alternators do not like to be bench tested. They'll put them on the fixture and connect a lead that runs them wide open. It heats and stresses the windings. It's a Jack Kevorkian test.

Ted

 

[Zach Smith]

dont wanna step on toes but he tested alternator not replaced it. but i ilke your suggestion of checking different areas instead of throwing money at it. like you said it could be something in wire

Oops, thought it was replaced...good catch.
I wear steel toes, and have a willingness to move my feet...so no problem here bud. He he. I'm never worried about someone helping... Sometimes I worry I'm being a pain though. the cool thing about this place is there are hundreds (I'm sure much more) of brains to pick and eyes to see.

 

[MWright936]

Thanks everyone for all the input! I will check wires and connections. I know the battery cables are clean and secure on the battery side, but I didn’t check anything beyond that when I replaced the battery. I’m a little ashamed to say I’ve never learned how to use a multimeter. I have a cheap one, and I think it works, but I’ve never really learned how to use it to test if things are working properly.

I have also very recently replaced my MAF and cleaned the throttle body.

 

[Zach Smith]

Thanks everyone for all the input! I will check wires and connections. I know the battery cables are clean and secure on the battery side, but I didn’t check anything beyond that when I replaced the battery. I’m a little ashamed to say I’ve never learned how to use a multimeter. I have a cheap one, and I think it works, but I’ve never really learned how to use it to test if things are working properly.

I have also very recently replaced my MAF and cleaned the throttle body.

Meh no better way to learn than trial under fire just check the reading with your new voltmeter on the batt first, so you have a standard to go by...and when ohming. Hold the two lead ends together to get your 0 point...the rest is just following point to point.

 

[silverado002]

Also, just a caution........ Never use the ohms range to measure voltage intentionally or unintentionally.

 

[MWright936]

I wanted to post a follow-up to close out this thread. I finally just took my truck to a trusted mechanic. He was a bit puzzled himself since the alternator was testing good. He put a new alternator on just to see if that did the trick, and it did. I don't know much about alternators, but he said the one on my truck is a 3-stage, and he figured one of the stages was bad, so it was working, but the bad stage was causing the flicker/pulse. Either way, new alternator fixed it, and all is well.

 

[silverado002]

Ok. You are good to go now. Congrats.

 

[Goldmember]

If its not the voltage regulator in the alternator, then somewhere in the exciter wire from the alt electrical plug-in through out is a bad connection or maybe broken wire.

Experienced something similar with my 97 silverado. As a quick fix, i hard wired the exciter wire directly to the alt hot post with a toggle switch. Did the trick ok, its just a matter of remembering to shut off the switch after shutting the truck off or possibly wake up to a dead battery. Let me kno if this works for u.

 

[Goldmember]

Oh, my bad. Didnt see that post about u solving the problem with a new alt! Good deal!