pulsing lights & runs rough on idle only

[01burban]

2007 Suburban LTZ 115k

 

So recently I have been noticing my dash lights, dome lights and exterior lighting (not head lights... explain that later) pulsating on idle. Whether the Voltage Gauge shows shows 14v or a reserved high 12v, on idle it pulses. Now Ironically I have also noticed my engine running rough on idle also almost around the same time the pulsing lights appeared. I installed a new battery about 6 month ago simply cause it was cold out the the old one died.

 

Now for the part that you may not want to hear but should know, I did install an HID headlight setup which also has some fancy LEDs in it but all was good until maybe a month after that when the pulsing appeared. Now the headlights are not even on when this happens so there is no odd draw or issues with the ballasts because there is simply no power being sent to them. When they do go on, it makes no difference to the pulsing lights throughout the truck during idle. Headlights stay perfectly solid and have no effect.

 

I have read many posts about pulsing lights coupled with rough idle. Many of these people have solved there issues with a new alternator. I would normally go ahead and replace it anyways being on 115k but I am on a tight budget and don't want to start repairing things just cause it worked for others. A reputable tech that backs up the Alt. suggestion would definitely put me at ease for that repair. Any other test or thoughts would be greatly appreciated.

 

regards,

Ron

[Jsdirt]

You'd have to measure alternator output with an old school analog meter, and watch for the corresponding fluctuation in voltage. That would settle it once and for all.

 

I'm betting the voltage regulator inside the alternator is going, or gone bad. If you find that this is indeed the cause, replacing just the v/r yourself (if you have the mechanical aptitude) would be the cheapest solution.

[01burban]

Good to know thanks! I did use a meter on the battery while engine is off which was about a 12.3. On start the terminals to the battery stayed solid around 14 and also solid at high 12 to a 13 during conservation mode. I did see any flucuating numbers on the meter but then again it was a digital one. I will try and dig up my old needle meter and check again.

 

I am very mechanically inclined but never changed out an alternator's regulator before, just didn't know you could. Doesn't these newer 07 and up vehicles have an external regulator that has conservation modes when voltage is not heavily needed? or is this all built into the alternator?

 

Ron

[Jsdirt]

Actually now that i think of it, this all might be controlled by the computer now. I know these new alts run on PWM signal - just not sure what's generating the signal. Has to be generated by the computer in response to alt. output & battery state-of-charge, I would figure. If that's the case, maybe the sensing wire has an issue.

 

Hate all this computer crap. Things used to be so cheap and easy to fix.

[01burban]

I could be way off but I thought I saw a video a ways back where someone replaced their alternator with one that had the old traditional Regulator within it and left the regulating plug harness that came from the computer unplugged and it ran fine. Not sure if it threw a code or not tho, or I was watching something totally different, can't remember.

[Jsdirt]

That would be a perfect solution, if it does indeed work. That's the route I would go.

[01burban]

I knew I wasn't going crazy... found the video

 

 

[01burban]

unfortunately the alternator in that video is an aftermarket High End unit thats supposed to self excite when power is needed. Not sure what the chevy stock alt will do if unplugged but i am willing to give it a try

[Jsdirt]

If you can get it to work, it'll probably outlast the truck.

[01burban]

so i unplugged the the connector at the top of the alternator and started the truck. I saw no difference... pulsing was still the same as when it was connected. Anyone know what that could point to as a possible issue?