Mysterious voltage drop. or is it?

[itsblown 10+ year member]

The car is a 2006 lt chevy trail blazer. It has the bose premium system in it with a pioneer double din 4400 head unit in it. We are gathering materials for a system install but one problem we ran into and this is before the addition of the aftermarket head unit is that when the car is parked or driving sometimes the head lights and over head lights will dimm even with no music playing and no HVAC. There is a whine comming from the alternator but when testing the batteries voltage while the car is idling it reads 14.4 volts.

Going to get the alternator tested right now, but if the battery is reading 14.4 volts while the car is idling doesnt that mean its putting out the correct power to it?

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[jteske88 10+ year member]

14.4 seems normal, I run between 13.00-15.00 volts. Should be charging just fine

 

[goingdef 10+ year member]

The car is a 2006 lt chevy trail blazer. It has the bose premium system in it with a pioneer double din 4400 head unit in it. We are gathering materials for a system install but one problem we ran into and this is before the addition of the aftermarket head unit is that when the car is parked or driving sometimes the head lights and over head lights will dimm even with no music playing and no HVAC. There is a whine comming from the alternator but when testing the batteries voltage while the car is idling it reads 14.4 volts.Going to get the alternator tested right now, but if the battery is reading 14.4 volts while the car is idling doesnt that mean its putting out the correct power to it?

have you checked to see if the cooling fans for the engine are coming on when the dimming occurs?

 

[audiobaun 5,000+ posts]

How about checking the battery with the vehicle off?Kinda sounds like that you may have loose connection/connections at the batt terminal also something to check

 

[gckless 5,000+ posts]

have you checked to see if the cooling fans for the engine are coming on when the dimming occurs?

^^This. Have you noticed anything else occurring at the same time? Even if voltage is good that alt might be putting out very little amperage if it's going bad, and any little draw would put a big strain on it. You shouldn't have whine without anything aftermarket on it. Usually though, failing alts will produce either less or more voltage. You have any way to test it easily?

 

[akheathen Premium Member]

is the whine the "alternator whine" playing through the stereo, or more of a bearing squeal? also, check your battery, and alternator plug. you should have a load-sensing ecm function that bumps the charging after a large load, like starting, and then runs only on-demand for economy. i had a few spikes in my system, but wiggled the plug a bit and it smoothed out to a solid 14.4. usually, if it is real noticeable, like in the lights, than there is a connection issue, or weak battery

 

[akheathen Premium Member]

just re-read... yah, it sounds like it is just running the charge rate high for recovery after starting. could go up to 15v for a little bit, and then drop down once it senses less current passing to the battery. if it gets higher, then that would be wiring.

 

[itsblown 10+ year member]

is the whine the "alternator whine" playing through the stereo, or more of a bearing squeal? also, check your battery, and alternator plug. you should have a load-sensing ecm function that bumps the charging after a large load, like starting, and then runs only on-demand for economy. i had a few spikes in my system, but wiggled the plug a bit and it smoothed out to a solid 14.4. usually, if it is real noticeable, like in the lights, than there is a connection issue, or weak battery

its bearing squeel

Alright heres an update, went to a battery and alternator place and had the battery and alt tested, The battery tested fine, and the alternator tested fine (it was charging correctly) however the noise the alternator is making is sounding like the alternator bearing and the guy at the battery/alternator place agrees and says that it will probably fail soon it has 140k miles on it

The check engine light was on and after a trip to autozone to find out what codes were comming up it threw a code for a bad I.A.C. iddle air control valve. Which will cuase the dimming over head lights. Looks like that needs to be cleaned/ replaced.

A new stock alt runs 170 dollars is there anyway that for a little bit more money we could get something that puts out a bit more power?

 

[akheathen Premium Member]

what size is yours? you can get a stock tahoe/denali/escilade 160a alt, which should bolt right in. with the bose sys, there might be a chance that is what you already have. yes, iac valves are notorious after a while, and with oil cooking. clean out your pcv/ tubuing, passages as well. i've seen several replaced, but that never fixes the real problem. if it is sticky, just clean everything real well. might have to actuate it to get it open, been about a year since i cleaned one out. on rare occasions, they might actually fail, but it is rare. fords are a different story. they just fail most of the time.

 

[akheathen Premium Member]

also, i checked around, and couldn't find an h.o. for under $300.... saw one drop to 275 used after i bought a new one, but vertex really hooked me up there. if it helps, i'd give ya $35 for yours.

 

[itsblown 10+ year member]

alright thanks for the help no idea on what the stock size is I didnt even think about checking out tahoe alternators

 

[itsblown 10+ year member]

This is the best deal I have found so far $250 for 200 amp alt by Knu so bassically 80 dollars more for 50 more amps

Knukonceptz product detail for 02-05 GM 4.2L DELCO 200A ALTERNATOR